Domestic hot water temperature UK

Domestic hot water temperature UK – a picture showing hot water flowing out of a tap

According to the HSE, domestic hot water must be kept in the cylinder at a minimum of 60 degrees Celsius to destroy legionella bacteria , which unfortunately can be fatal for human beings.

Therefore, the best temperature or ideal temperature for your hot water tank is 60 °C, as 90% of the bacteria will die in only two minutes if the hot water tank temperature is 60 °C. If the temperature of the hot water tank is raised to 70 degrees Celsius, all of the Legionella bacteria will die right away.

Hot water tank temperature for your hot water cylinder

In the UK, the hot water tank’s temperature should range from 60 °C to 65 °C.

There is a higher chance of bacteria like Legionella, which causes Legionnaires’ disease, developing if the temperature is below 50°C. When your water has been sitting in the stored hot water tank for some time, this occurs.

The water will be too hot to use and the danger of severe burns will rise if the temperature rises over 65°C. The water is hot enough to use and hot enough to destroy harmful bacteria when kept at a safe temperature of 60 °C to 65 °C.

Hot water cylinders or tank

Hot water tanks must now be equipped with a thermostat that allows the user to control the temperature of the water within. You can monitor the hot water tank temperature of the tank on your phone these days using a hot water temperature sensor installed in the hot water cylinder.

unvented hot water cylinders indirect

Cut away picture of our indirect cylinder Flexiheat UK

Our indirect unvented cylinders or direct unvented cylinders that we supply both have a thermostat to control the hot water temperature to your requirements.

Legionella, what is it ?

The word “legionellosis” refers to a group of illnesses brought on by the legionella bacteria, including the most severe one, Legionnaires’ disease, as well as the comparable but less dangerous Pontiac fever and Lochgoilhead fever. The potentially lethal pneumonia known as Legionnaires’ disease can infect anyone. Age-related risk is higher for certain people than for others, such as:

  1. Any person whose immune system is compromised

  2. Those with chronic kidney or respiratory diseases.

  3. People suffering from cardiovascular, pulmonary, and diabetes diseases.

  4. Those who smoke and drink heavily.

  5. Individuals who are over 45 years of age

In natural water sources, including rivers, lakes, and reservoirs, the bacterium Legionella pneumophila and related bacteria are widespread but often in low concentrations. They may also be found in specially designed water systems, including spa pools, evaporative condensers, cooling towers, and hot and cold water systems.

In order to reduce the dangers of legionnaires’ illness, it is crucial to eliminate favourable circumstances for legionella risk.

How does one get legionnaires ?

People get Legionnaires’ disease by breathing in aerosolized water droplets (aerosols) that are suspended in the air and carry the bacteria. The following circumstances raise the risk of legionella:

Legionnaires disease caused by low stored hot water temperatures in hot water cylinders in the UK


The hot water temperature in the system may range from 20 to 45 °C in the hot water cylinder or domestic hot water system, which is ideal for development.

It is possible to produce and disperse breathable water droplets, such as aerosol, from a cooling tower or hot water outlets, such as sink taps, bath taps, or showers.

When water is stored and/or recirculated, deposits like rust, sludge, scale, organic waste, and biofilms can help bacteria grow and feed the organism.

Thus, it is vital to reduce the risks to the health of individuals, be they staff or customers on your business site, or home owners or occupants.

The majority of people who become ill and require hospital treatment ultimately survive and recover completely.

However, roughly one in ten individuals who contract Legionnaires’ disease passes away from the illness.

What temperature should domestic hot water be in the UK

We’ve established that is hot water tank temperature should be 60 C to 65 degrees Celsius which means that any gas boilers or oil boilers should be supplying the indirect cylinder with a hot water temperature above that figure to ensure the cold water coming into the hot water cylinder gets heated up to the right temperature.

Alternative methods of heating the hot water tank, such as a solar water heating system or heat pumps, are also becoming more common these days as we look to reduce and save carbon emissions from gas boilers or oil boiler heating system.

There are some issues with regards to using heat pumps instead of a heating boiler, as they can struggle to heat the water system, as at present the maximum heating temperatures of a heat pump are around 55 °C, which means they don’t generate the right temperatures required for domestic hot water heating.

This is remedied by using an immersion heater to raise the tank water temperature from 55 degrees Celsius to the required 60 degrees Celsius.
The immersion heater or heaters, depending on the hot water tank size, are normally electrically supplied with power.

Combi boilers, on the other hand, produce hot water on demand and have no stored hot water tank. Thus, these types of gas or oil boilers can supply the hot water system at lower hot water temperatures , which also helps save carbon emissions, energy and money for your economical domestic hot water heating system.

The hot water tank accounts for 14% to 18% of the energy consumed by the typical household.

Domestic hot water systems in the UK

There are two main systems for heating hot water used in the United Kingdom.

Stored domestic hot water

normally produced via a boiler in conjunction with an indirect cylinder. The thermostat on the hot water tank controls the boiler, which you simply adjust to your requirements.

On demand or instant hot water:

An on-demand water hot system normally saves energy and money ( normally around 30% less energy when compared to hot water storage systems ) as they efficiently allow the bath, shower, and tap water supply to be at a lower temperature—around 40C to 43C while washing. This warm water temperature eliminates the risk of scalding when having a shower, bath, or using a hot tap as this heated water is under the supply temperature of 44°C at which scalding risk to vulnerable people can occur.

Instant water can be provided by a gas water heater , which we have a full range detailed on this dedicated webpage: gas water heaters , which are available in natural gas or LPG (Propane) gas.

gas water heaters energy efficient hot water heating from Flexiheat UK

Gas Water Heaters

In many households in the UK , a combi boiler or combination boiler is the most commonly used appliance as they do both the heating and water system. The boiler has a thermostat, which allows temperature control of the DHW water.

This thermostat dictates the water temperature to the supply pipe running to your warm water outlets, such as your hot water tap, shower, or bath tap.

As the boiler doesn’t have to heat the water up to 60 °C like a stored warm water tank, they benefit from lower energy requirements and eliminate scalding potential .

Our combi or combination boilers are detailed on this webpage: LPG combi boilers. We also do these units in natural gas too.

combination boiler from Flexiheat UK

Combi boiler  from Flexiheat UK



The hot water temperature for your hot water tank will be different to the hot water temperature used on an instant water heater , as the stored warm water must be 60C or over, and when producing it on demand , it can be lower, circa 40-43C, depending on your requirements to save energy.

Industrial water heaters Gas or Electric

Hot water systems

Industrial hot water heater or hot water heating via indirect water heaters or an on-demand water heater - Flexiheat UK

An industrial water heater provides a domestic hot water system – also know as DHW – which delivers hot water to fixtures used by people at the sink, in the shower, or bath and any other location where warm water may come into contact with humans for bathing or washing up etc. Hot or warm water may also be required for food and beverage commercial and industrial applications, processing or wash down industrial applications in abattoirs etc.

Commercial and industrial applications

Hot water systems or water heaters for commercial or industrial applications can cover hot water requirements for-

Commercial applications – commercial water heaters

Locations such as hospitals, hotels, swimming pools, schools, camping facilities, or sports or leisure centres may be considered commercial hot water heating applications, and thus require commercial water heaters, but we would consider a hospital, due to the way they operate and the capacities of domestic hot water they require, which can run into thousands of litres of warm water per hour.

On demand water heater or water heating for health care environments Flexiheat UK

Hot water systems for hospitals or health care environments


But there is no hard and fast rule when it comes to commercial water heaters, and when a commercial water heater becomes an industrial water heater as such.

A picture of indirect water heaters in a hospital hot water heating system Flexiheat UK

Indirect Water heaters – for a hospital or a food or beverage processing plant water heating requirements


Most people go with the gas safe qualifications, in that for any gas appliance over 70kW input, the heating installer must have an industrial gas certificate or qualification to do the installation, so this seems like a good defining point when it comes to the difference between commercial water heaters and industrial water heaters.

Industrial hot water heaters

Industrial hot water systems or hot water heaters tend to be installed, developed and designed for process hot water applications such as food production, preparation, or wash down services, which can require high levels of hot water supply with regard to litres and often at high water heating temperatures.

high pressure hot water heating systems or products for food and beverage production with Andrews water heaters services

Solutions for warm water requirements for food and beverage production by Flexiheat UK

These factors make our gas water heaters our most popular product range when it comes to solutions for water heating systems. Because gas delivers a remarkable amount of energy through a relatively small pipe, and because of recent legislative changes, any industrial gas water heater must now be condensing to provide maximum efficiency and benefits in reducing greenhouse emissions.

A water heater for a process application is normally just a simple calculation of the volume of water required and the temperature rise required.

Heat pump hot water heating

Heat pumps aren’t suitable water heating solutions at present as they can’t achieve the required water temperatures that the customer often requires, as heat pump systems can only achieve a temperature in the 50 to 55C range. To get up to the required stored water temperature of at least 60 °C, they have to use electric immersion heaters to top up the heat supplies—in essence, they can be called hybrid water heaters.

Whether the technology for heat pumps develops so they can achieve the higher hot water temperatures and kW capacities is to be seen. Hopefully so, as they have high efficiency. If you have the power supply available, as these units normally require a 3 phase electrical connection and take up a lot of space as storage tanks are normally required as accessories.

At present, heat pumps products aren’t really suitable for domestic water heating systems for commercial and industrial applications.

Electric water heaters

We have a dedicated electric water heaters web page that goes into full detail on the capacities in litres of the tanks and kW ratings available here.- Electric industrial and commercial water heaters

commercial electric water heaters; commercial electric hot water heater; industrial electric water heater; industrial electric hot water heater;

Commercial & Industrial electric water heaters from Flexiheat UK

Industrial gas water heaters

As mentioned previously, our gas water heater range is the most popular hot water systems for industrialised requirements due to the high pressure, kW, and heat output the range can produce.

The cost-to-output makes this water heater range a favourite with many a trading customer of ours.

We do a range of gas instantaneous water heaters with an output up to 300 kW which can provide up to 174 litres / minute of domestic hot water, with a high modulation ratio of 1 to 60.

instantaneous gas water heaters; gas water heaters in cascade; lpg multipoint water heater; gas fired condensing water heaters; condensing water heater;

instantaneous gas water heaters- condensing in cascade complete with pipework rig from Flexiheat UK

Full details are listed on our dedicated gas water heaters webpage here – industrial gas hot water heating 

Or we can use these units with a DHW storage tank to account for peak demands or loads which are often found in process applications – these are detailed here – Domestic hot water storage tanks 

Contact us

Should you require any more support, selection and design expertise or cost on our industrial water heating products for commercial and industrial applications with high capacities in terms of litres and kW output, then please fill out your details on the contact us form page on the website, or feel free to contact our UK sales team professionals on 01202 822221 who are on hand to support and assist you with any part of your hot water heater project. Follow us on Facebook or Twitter for an overview of our latest news and products.

Main multipoint bf water heater new replacement

Main multipoint bf water heater which is a gas fired instantaneous hot water heater

If you are looking for a main multipoint BF water heater, then the bad news is that these gas fired water heaters are no longer available, whether it was the standard model, which was obsolete in 2018, or the ERP model, which was discontinued in 2019.

This gas-fired instantaneous water heater brand and model was an advanced balanced flue 24 hour a day space-saving on-demand water heating unit with no storage tank and a copper heat exchanger.They were a hot favourite for hot water heating for small homeowners’ domestic needs as they eliminated the requirement for a separate hot water cylinder and had a modern room sealed design.

The balanced flue water heater had a Piezo igniter and a permanent pilot. This meant that it didn’t need electricity or batteries.

In these main hot water heaters, the pilot light stayed on at all time. Because the pilot flame was continually on, this burned up and squandered gas, which was bad for energy bills and the environment.

A few years ago, “Which” consumer magazine conducted a cost analysis that revealed that a pilot light cost an incredible average of £97 per year to run.

The ErP legislation for efficency with regards to water heaters means that permanent pilot water heaters mean that these types of units no longer meet the required efficency levels, which is the reason why they are not available anymore.

Electronic ignition models now prevail, and due to the elimination of pilot lights, they end up saving money on running cost.

Now the water heaters must have an electricity supply – just a standard 240 volt – 1 Phase supply.

Main multipoint bf gas water heater

There are some companies offering spare parts for these advanced balanced flue main water heaters, such as the gas isolation valve kit, the thermocouple kit, overheat protection device kit, air vent, and main heat exchanger ( although the price of a replacement heat exchanger is more than a new replacement water heater—i.e., to replace the heat exchanger is no longer viable as the item costs more than a new gas-fired water heater, let alone the cost of a plumber to fit the replacement spare parts)

Should you need to check the gas supply inlet pressure or burner pressure to make sure that the rate of gas is correct, or change the gas isolation valve, then this needs to be done by a qualified gas safe engineer.

It is important to ensure that any suitable service or services such as replacing parts on gas water heaters or gas-fired central heating boilers, should not be attempted by a homeowner or a plumber that doesn’t have the gas safe plumbing qualification.

Main multipoint water heater

A balanced flue system

On demand gas water heaters that employed balanced flues are made up of two pipes with one pipe contained within the other. The outer pipe brings in the fresh air from the outside that is necessary for the combustion process to occur, while the inner pipe serves the purpose of removing the waste gases from your property. Depending on the main instantaneous water heater you purchased, the designed flue system may either go horizontally through an outside wall or vertically through the roof to suit the customers requirements.

The balanced flue model had to be installed on a wall with direct access to the external air environment-see diagram below.

A picture of the balanced flue kit for main multipoint gas water heater – Flexiheat UK

Balanced flue kit details


Main also did a fan flued version of this gas water heater, which was designated the main multipoint FF ( fan flue) —this unit is the one that could be vertically or horizontally flued and didn’t need to be installed on an outside wall of the property because of the fan flue system.Again,these fan flue water heaters were a hot favourite with homes or locations that had a big demand for hot water but didn’t want to use a hot water cylinder or storage cylinder.

main fan flued multipoint gas fired water heater flue options Flexiheat UK

Main fan flued multipoint – Flue options


Hot water instantaneous heater – Balanced Flue Main Heater

So now for the replacement of the Main multipoint water heater in its balanced flue version. Firstly, the dimensions of the unit are

Main balanced flue water heater dimensions from Flexiheat UK

Main bf multipoint water heater dimensions


and for our replacement unit – the SF14 Low NOx gas fired water heater with its modern room sealed design.

SF14 on demand water heater dimensions Flexiheat UK

As you can see from the above dimensions, our SF14 Low NOx is smaller in size, yet still has plenty of room for the unit to be maintained and to service, with all the plumbing connections at the bottom of the unit.

lpg tankless water heaters; lpg instant water heaters; liquefied petroleum gas hot water heaters

SF14 – tankless water heaters from Flexiheat UK – Internal picture of the hot water heater

SF14 Product benefits and features

  • Wet chamber copper exchanger that prevents thermal inertia; With large 16mm diameter water ways – so it benefits from very low pressure drops, guarantees lower risks of clogging,greater thermal efficiency, and greater ease of cleaning.
  • Self-diagnostic electronic board;
  • Ease of access and maintenance;
  • Possibility of integration with other renewable energy source (e.g. solar panels)
  • Possibility of remote shutdown;
  • Overheat protection device
  • Reduction of initial overtemperatures with low withdrawals:
  • Degree of electrical protection: IPX4D;
  • Very low NOx emissions, maximum 50 mg / kWh.
  • Modern room sealed design

Because of their sleek, refreshingly modern designs and outstanding reputation for reliability and highest quality this versatile range of water heaters has siting flexibility with various flueing options.

Download the SF14 Low NOx gas fired water heater manual Flexiheat UK

Hot water performance table

The main water heater will produce the following hot water rates, depending on the temperature rise as per the table below.

A table showing the hot water performance of the main multipoint water heater gas fired

Our SF14 water heater model , which has a Domestic maximum nominal heat output of 24.5 kW will produce the following hot water flow rates.

flow rates of our SF14 gas instantaneous water heater

Water heater gas supply

The main multipoint bf water heating unit, as far as we can see from the details, was only available in natural gas, which is category or classification G20 . This is what we refer to as natural gas in the UK, and is the gas that flows from the main gas supply services, or network.

Our replacement for the main multipoint bf or the fan flued models can be powered by either natural gas or propane gas ( LPG ). The LPG version can be fuelled by either a 47Kg propane tank or cylinder , or alternatively by a bulk storage propane tank.

We keep stock of our SF14 low NOx gas water heaters in both gas types in our warehouse , ready to service any immediate order without delay.

Experts in the water heating industry

If you require any more info, correct hot water heating solutions advice, check stock, delivery times, require trade prices or order your replacement for the main multipoint BF water heaters, range then please use the contact us form page on the website, or alternatively feel free to contact our customer service team experts a call on phone number 01202 822221-Flexiheat UK.

Room sealed lpg water heater

room sealed lpg water heater powered by propane Flexiheat UK

Room sealed LPG water heater – Flexiheat UK

Room sealed water heater

 A room sealed LPG water heater is water heater that draws combustion air from outside, and any waste gases ( also know as combustion gases or flue gases ) are sent outside rather than into the room.

Thus, when you have a room sealed water heater, this means that you can work or sleep in the same area, such as shower rooms or bedrooms, where the room sealed LPG water heater is installed in total safety, without the risk of fatal carbon monoxide poisoning.

Today, most LPG water heaters are room sealed and use full electronic ignition for maximum energy savings, ensuring minimal gas consumption and maximum savings as compared to the older pilot light type of LPG water heater.

The pilot light, or pilot flame, remained on all the time in older LPG water heaters. This consumed and wasted gas, which was not good for the fuel bills and the environment due to the constant burning of the pilot flame.

“Which” consumer magazine did a costing a few years ago, which showed that a pilot light cost an astonishing average of £97 per year just to operate.

That’s why these days a full electronic ignition LPG water heater are favoured and are standard unit for virtually any location such as a static caravan, log cabins, shower rooms or any suitable place that requires efficient water heating for their domestic hot water requirements.

Propane or LPG gas

Propane gas or LPG gas water heaters are used predominately in areas where mains gas, which is natural gas, is unavailable, such as log cabins , static caravan parks or we have even supplied our room sealed LPG water heater range for shepherd huts, as the maximum power consumption is a very low 36 Watts for our most common room sealed water heater, which is our SF14 model.

The unit can be powered by either an LPG gas cylinder or a bulk propane gas storage tank. An LPG gas cylinder is often used to power a static caravan.

Domestic hot water heater

Our most common domestic water heater that is powered by propane gas is our 24 kW , which is designated our SF14 Low NOx evolution model.

This unit will operate with an extremely low water pressure water supply (only 0.5 Bar is required ) and low flow operation.

This room sealed water heater can be used on a 12 volt electric system with the use of a small inverter due to the maximum power consumption only being 36 watts. So they can be fitted in virtually any location, such as horseboxes, shepherd huts with no mains electricity, in remote locations or even narrowboats, as the unit can be powered by a small inverter on a 12 volt system.

SF14 Low NOx instantaneous water heaters have the following features:


internal picture of a room sealed water heater lpg gas fired from Flexiheat UK

Internal picture of the room sealed LPG hot water heater ,showing the de-oxygenated copper heat exchanger with large 16mm water ways

  • Wet chamber de-oxygenated copper heat exchanger that prevents thermal inertia in low flow operation with large 16mm water ways

  • Excellent thermal efficiency for maximum savings and great flow rates.

  • LCD display shows the temperature of the water being generated, and displays any fault codes should they ever pop up. The fault codes will tell the user exactly what the problem is, such as low pressure etc. Problem finding and solving is easy.

  • Electronic control board with self-diagnosis-ensure constant monitoring of the room sealed LPG water heater. Water flow and water temperature are continuously monitored by a microprocessor to provide safe and effective water heating with minimal gas usage.

  • Electronic ignition: Automatic ignition ensures no liquefied petroleum gas is wasted on a pilot light and minimal gas consumption.

  • Ionization flame control with full electronic ignition.

  • Adjustable water temperature of 35 to 60 degrees Celsius on the LCD display.

  • Reduction of initial high water temperatures with low flow rates

  • It will function on an extremely low water pressure of only 0.5 bar and with low flow rates.

  • Industry standard horizontal flue kit or vertical flue options allow you to choose the suitable place to install the efficient water heating device in total safety.

  • Fitting kit: our standard fitting kit includes all of the copper pipework tails as well as an isolating gas valve, cold water flow valve, and hot water outlet valve, reducing installation time.

  • It can be fuelled by either LPG gas cylinders or propane gas cylinders. We recommend 47 KG propane gas storage cylinders as these can supply 33.8 kW of continuous domestic hot water heating per hour, which is more than the gas input of the SF14 water heaters, which is 24 kW.

  • Because they can use portable gas cylinders, they are the best option for instantaneous water heaters for log cabins or static caravans in remote locations without a mains gas supply.

  • A direct replacement for replacing older Morco or Forcali water heaters.

  • Maximum power consumption is only 36 watts.
  • Install in virtually any location in total safety – shower rooms, shepherd huts or a static caravan etc.

Dimensions for the SF14 tankless heaters

SF14 on demand water heater dimensions Flexiheat UK

For warranty purposes and safety all of our lpg water heaters should be installed by a LPG qualified gas safe engineer.

Download the SF14 Low NOx gas fired water heater manual Flexiheat UK

Flue kit

The industry standard horizontal 60/100mm balanced flue kit.

Horizontal flue kit for SF14 domestic hot water units

or vertical flue kit option

Vertical flue kit for SF14 domestic hot water units

Water heating with combustion sealed LPG water heaters

Should you require any more support, selection advice, or cost/quote on our room sealed LPG water heater range with flow rates, then please use the contact us form page on the website, or feel free to give us a call on 01202 822221.

Domestic hot water storage tank

Domestic hot water storage tank or vessel

With regards to a domestic hot water storage tank or vessel , first we have to define what domestic hot water is in relation to a storage hot water tank or hot water cylinder.

Domestic hot water

Domestic hot water is the heated potable water that feeds taps, showers, baths, or the kitchen hot taps. It is also referred to as sanitary hot water. The hot water is heated up from the cold water mains temperature to the recommended temperature for storing hot water of at least 60 degrees C.

The cold water enters or that feeds the hot water tanks can either be mains water supply at mains water pressure or via a cold water storage tank/cold water tank – (often called a header tank) that is used on a vented hot water cylinder.

It is then heated up via water heaters , which can use various heat sources such as gas, oil, or an electric heating system. This hot water is then stored in a hot water storage tank, which is designed to retain heat as a thermal storage tank for use when there is a demand for the hot water, which is often a large load, in a short period of time.

They essentially serve as water reservoirs, and they’ll be connected to either an indirect or direct fired hot water system to increase hot water storage volumes to accommodate high demand applications with thermal storage.

A hot water storage tank or hot water storage vessel is also known as a hot water buffer tank because it “buffers” hot water loads during peak hot water demand.

Hot water storage tanks

A hot water storage tank or vessel, just like its counter parts, such as indirect cylinders or heating products, must also be energy efficient water cylinders and must carry an ErP energy efficiency rating for standby heat loss.

Any hot water storage systems must comply with the Eco-design ErP Directive.

On September 26, 2017, restrictions on hot water storage tanks’ standing heat losses (heat lost to the surroundings equals wasted energy) were implemented to ensure maximum efficiency.

Storage tanks, or cylinders with a capacity of 2,000 litres or less must meet a minimum energy performance standard in order to be sold legally in the UK and the EU. The same applies for a thermal store.

The rate of heat loss determines the energy rating of a hot water storage tank , which is measured in watts. The insulation of the hot water tank is crucial to achieving a high efficiency band since each efficiency band has a minimum and maximum heat loss proportional to capacity. The best hot water tanks have a thick layer of high-performance polyurethane foam to cover the gap between the tank and the cover.

As part of the energy labelling directive, which says that all energy-related products, like home appliances, must show their efficiency rating in a clear way, hot water storage tanks with a capacity of 500 litres or less must also have energy labels.

Our entire hot water storage tank line complies with both ErP and the energy labelling directive and can be fitted with additional electric immersion heaters or a single immersion heater as additional heat sources to top up or as a backup heating system to the primary water heating system.

hot water cylinder

Is it a hot water cylinder, a thermal store, a hot water tank, or a buffer tank?

Ultimately, they are just a storage tank for hot water—you can call them what you want.

hot water storage tanks or cylinders for domestic hot water accumulation from Flexiheat UK

In simple terms, they are hot water storage tanks heated by other heat sources designed to store hot water for peak hot water demands or loads, normally for domestic use hot water or a process water heating system such as warm washing down systems demand etc.

They are not an indirect hot water cylinder heating system that uses a boiler (normally condensing boilers) or solar panels to heat the surrounding water in the hot water cylinder via a heat exchanger coil within the storage tank or hot water cylinder. Thus the term an indirect cylinder.

Hot water tank range

We do various types of cylinder or tank, these being – glass lined ( vitreous enamelled ) or stainless steel in construction-

Vitreous enamelled DHW tanks

Vitreous enamelling is an impermeable, food-safe coating that looks like porcelain and protects the metal surface of a storage tank when it comes in contact with water.

In addition to the test temperature required by current standards (22 degrees C), our vitreous enamel has a food grade certification at 120 degrees C. This makes sure that it is of the highest quality, even at high operating temperatures.

The maximum operating temperature of an enamelled storage tank

Because of their capacity for molecular interaction with the steel surface, these hot water storage tanks can withstand a maximum DHW storage heated water temperature of 95 degrees C without deterioration or detachment.

Pressure rating and warranty period

These warm water storage tanks, are 8 Bar pressure rated and come with a 5-year warranty


hot water storage tank 200 to 1500 litre dimensions – these cylinders are fed by a sperate water heater often tankless water heaters or instantaneous water heaters which heat the water and then it is stored in one of these tanks or cylinders

200 to 1500 Litre Warm Water Storage Tanks – CV-R range


Dimensional detail of our hot water storage tanks – The “R” range have a inspection / clean out port which is 146mm in diameter as standard – item “J” on the drawing – we can also fit an immersion heater in this port as well.

Domestic hot water storage vessel range 200 to 1500 litre technical data from Flexiheat UK

Rigid, mould-injected PU thermal insulation that has demountable sections that allow you to get the 800 and 1000 litre hot water cylinders through a standard 800mm doorway.

800 and 1000 litre hot water cylinders that can fit through a standard 800mm doorway

Demountable thermal insulation on the 800 and 1000 Litre

Commercial hot water storage tanks

We do a full range of commercial hot water storage tanks or industrial hot water tanks all the way up to 6,000 litres

These large-capacity commercial and industrial hot water tanks have both side and top DN 400mm manholes to access the interior of the storage tank for inspection, cleaning, and maintenance tasks.

Thermally insulated with rigid, mould-injected, 80 mm-thick, polyurethane foam, with an insulating piece in the same material on the DN400mm side manhole.

As standard, Correx permanent anode (cathodic) protection units are included, which are special titanium anodes that emit the necessary current for the metal surface to be protected via an automatic potentiostat connected to the main power supply.

Maintenance free: since the cathodic protection system is permanent, unlike sacrificial anodes, there is no degradation, and no replacement of the anodes is necessary.

commercial hot water storage tanks 1500 to 6000 litres by Flexiheat UK

1,500 to 6000 litres commercial or industrial hot water storage vessels, tanks or cylinders


Dimensional detail of our commercial hot water storage tank range


commercial and industrial hot water tanks technical data 1500 to 6000 litres Flexiheat UK

stainless steel hot water storage tank

Stainless steel hot water tanks have become an increasingly popular type of domestic hot water storage tank as they have many benefits.

  • Stainless steel hot water tanks do not require a sacrificial anode , unlike an enamelled or glass-lined hot water tank or hot water cylinders.

  • This means that the inspection and maintenance regime of a stainless steel hot water tank is less than that of enamelled hot water cylinders.

  • Stainless steel storage tanks or hot water cylinders used to have a working pressure advantage over enamelled storage tank versions, but these days the hot water tanks are equal in the pressure rating.

stainless steel domestic hot water storage tanks flexiheat UK

Dimensional detail of our stainless steel domestic hot water storage tanks

Stainless steel domestic hot water storage tanks 200 to 1000 litre technical data from Flexiheat UK


Insulation of the storage tanks

The insulation keeps the temperature of the DHW storage at a constant level for extended periods of time without requiring extra energy input. It is an over-sized, rigid, mould-injected PU thermal insulation. This results in fewer external energy source start-ups (such as tankless water heaters), which reduces energy usage, which directly translates into actual energy cost savings.

Hot water system

A vented cylinder must feature a vent pipe that allows the water to expand as it warms up in the storage tank and safely condenses any residual warm water into the cold tank. To maintain water pressure to the vented cylinders, there must be “head” or distance above the tank or vessel, which is why the stored cold water tank is often located in the attic space in UK homes.

On the other hand, unvented cylinders, or buffer tanks, are a sealed domestic hot water heating system. The expansion of the domestic hot water as it heats up is taken up by an expansion vessel in an unvented cylinder or unvented cylinders.

Should you require any more support, selection advice or costs/ get a quote on our domestic hot water storage tank range , with fast delivery times then please use the contact us form page on the website, or feel free to give us a call on 01202 822221.

Dual Fuel Boilers – Gas and Oil Fired

duel fuel boilers natural gas and oil fired for hot water systems from Flexiheat UK

Dual Fuel Boilers – Natural gas or propane gas (LPG) and oil fired

Dual fuel boilers can keep a critical heating system operating, such as a hospital, for example, even if the primary fuel supply fails or is unavailable. They are often referred to as “dual fuel heating system”.

When it comes to hospitals and industrial operations or processes, where boilers provide heating hot water and/or domestic hot water, any loss of these vital processes can have a big effect on the health of patients and the bottom line of a company.

The other benefit is that a dual fuel boiler heating system allows you to swap your fuel depending on what’s the cheapest option. You have the choice to reduce your energy bills by using whatever is the cheapest option when using these heating systems, either as a short or long term solution.

Also, fuel security benefits: should there be an issue with supply problems of either gas or oil, you can simply swap over to what is available without having to buy a new boiler or new burner, which cuts down installation costs . You could even call duel fuel boilers a hybrid system or hybrid heating as such.

Why use a dual fuel boiler?

While most boiler installations have some form of backup system, normally in the form of additional boilers for the heating systems , in the event of a fuel loss rather than a boiler breakdown that interrupts vital heating system operations, a second boiler that utilises the same fuel will not offer any degree of redundancy to the boiler system.

Therefore, the requirement for a dual fuel system to eliminate this potential failure of a single fuel heating system or boiler system.

commercial boilers with dual fuel oil gas burners -hybrid heating system


The dual fuel or dual energy boiler is better: if one fuel supply fails, the second quickly takes over, and your facility’s heating and hot water output are unlikely to be interrupted.

Changing from one energy source to another based on which is more economical for your dual fuel boiler is a great choice for property owners.

Where essential processes exist, a dual or multi fuel boiler that can use a consistent supply of natural gas in normal operation and convert to a secondary source of fuel (such as oil or LPG) if the natural gas supply fails provides a high level of redundancy.

Dual fuel heating system

The most popular dual fuel boilers are a combination of gas and oil . The gas side of the dual fuel burner can be natural gas, which is your mains traditional gas, or propane liquid gas, also known as LPG gas.

For any old or new boiler, annual servicing by a heating engineer is recommended to ensure that the central heating systems are operating effectively, efficiently, and ready for the colder months.

Dual fuel commercial boiler

All heating boilers from 70kW to 400kW have to be condensing to comply with the UK Part L building regulations (Conservation of fuel and power-standards for the energy performance of new and existing buildings) for commercial buildings, which have strict energy efficiency requirements to help reduce carbon emissions , whether they are an oil boiler or a gas boiler or LPG fired boilers. The single fuel type doesn’t matter-they all must comply with the regulations.

A dual fuel boiler at this kW output range must also comply with the efficiency requirements just because its dual fuel makes no difference.

Even though both gas an oil are ultimately fossil fuels and produce greenhouse gas emissions, the use of a condensing boiler reduces these fossil fuels impact to the lowest possible level as the highly efficient boiler system extracts the most energy from the fuel source.

Heating boiler range

Condensing boilers are the only option for fixed or permanent duel fuel boiler installation with outputs ranging from 70kW to 400kW.

Our condensing dual fuel boiler range has some unique advantages or benefits in that you can have two different temperature heating circuits from the boiler: one can be a low temperature heating system such as a 50/30c flow and return temperatures , and the other can be a higher temperature heating system with an 80/60C flow and low and return temperatures, which is ideal for heating an indirect hot water cylinder for your domestic hot water requirements.

You need higher temperatures from your heating boiler to be able to heat the domestic hot water up to 60°C. If your boiler can only produce one temperature and is being used on a low temperature heating system of 50 °C, for example, that temperature would not be enough for the heat exchanger in the hot water cylinder. Electric heating in the form of an immersion heater would be required in combination to increase the temperatures further in the installation and achieve the 60 degrees C required for a stored hot water system.

And electricity is an expensive energy source to use for a heating system.

Condensing boiler option – from 66 kW all the way up to 1,550 kW of output dependant on temperatures run


boiler technical data for dual fuel heating systems

Condensing Boiler Option

We would always recommend our condensing boiler option for a few reasons

  1. They are more energy efficient – 102% at full load 104% at part load in condensation mode
  2. There is no lower limit on the return water temperatures
  3. The combustion chamber and heat exchanger pipers are manufactured in stainless steel AISI 316L – this ensures long product life
internal picture of a commercial boiler Flexiheat UK

Internal picture of our condensing commercial boiler with stainless steel wetted parts

But technically, after 400kW of output, you don’t have to have condensing to comply with the building regulations – they must, however, comply with the following efficiency levels – but very few boilers do if they are not condensing.

Minimum heat generator seasonal efficiency for boiler systems in existing buildings part L regulations

Part L building regulations efficiency requirements


We also supply another range, which can be used in temporary on non permanent boiler applications  – as they not require to meet the efficiency levels of Part L  as far as we understand, but please do your own due diligence.  

technical data for boilers above 400kW for dual fuel burners Flexiheat UK

These boilers must always operate in forced circulation hot water systems and with a minimum return temperature of 55 °C. So, you need to use a shunt pump, which also provides an anti-condensation function for the boiler combustion chamber, installed between the flow and return connections, upstream on the heating systems with a 3- or 4-way mixing valve.

Dual fuel burner

At the heart of every dual fuel heating system is the burner.

Dual fuel burners give you the option of using gas (natural gas or propane) or oil as your energy source, depending on your business or operational needs.

The most popular dual fuel systems are natural gas and 35-second oil, which is also known as gas oil or red diesel . As such, you get two technologies or two burners in one installed unit.

dual fuel burner natural gas propane gas and oil options for dual fuel boilers Flexiheat UK

Dual fuel burner – Gas and Oil

There are various options for your dual fuel burner-

  • single stage burner option up to 232kW output-with high efficiency


  • For large efficient heating system demands, 2 stage Hi-Low burner, 2 stage sliding or fully modulating dual fuel burner options are available.
  • Manual changeover as standard or automatic fuel changeover as an option for your dual fuel boiler

Multi-fuel burner standards

All our dual fuel burners conform to all the relevant CE legislation and quality standards where applicable –

• EMC Directive 2014/30/UE

• LVD Directive 2014/35/UE

• Directive MD 2006/42/CE-2006/42/EG-2006/42/EC

• PED Directive (Article 4, Section 3)2014/68/EU

• EN676 (gas)-EN267 (liquid fuel)-EN746-2 (industrial thermo processing equipment technologies) are the reference rules.

If you require any products support, heating solutions advice, check stock, delivery times or require a price on our dual fuel boilers or dual fuel heating system from Flexiheat UK, then please use the contact us form page on the website, or alternatively feel free to give our customer service team experts a call phone number 01202 822221.All rights reserved Flexiheat UK.

Gas Water Heaters

gas water heaters energy efficient hot water heating from Flexiheat UK

Gas Water Heaters

A gas water heater or gas fired water heater is used to produce domestic hot water for your flat, house or commercial property. This hot water is of sanitary quality and is used to feed showers, baths, and hot water taps or faucets.

Water heater gas fired

One of the many benefits of a gas water heater is the energy delivery that it can dissipate into the water and thus the good flow rates they can achieve when compared to instantaneous electric water heaters, which require a lot of Amps and normally a three-phase electric supply to achieve similar flow rates.

Gas fired water heaters

Our entire range of gas fired water heaters can be powered by either mains gas (also known as natural gas) or LPG (propane gas), which is your liquid gas. It is easy to convert our gas fired water heaters from one type of gas to another via a simple-to-fit gas conversion kit.

Hot Water Heaters

Gas fired water heaters can be split into two main categories:

On demand water heaters

On-demand, tankless water heaters or instantaneous water heaters will use less energy than storage water heaters and are the most energy-efficient method for heating water, with high performance mains pressure to all warm water outlets. However, the instant hot water flow rate demand and the usage of the hot water outlets by the customer installation must be considered to ensure they’ll work correctly. We go into more depth on this range here – instantaneous gas water heater

Storage hot water heaters

Alternatively, we do a range of storage water heaters; the two stock units have a water storage quantity of 150 litres, which is ideal for customers with a larger demand for domestic hot water, such as having a periodic requirement for a larger volume of water in a short period of time that an instant hot water heater couldn’t service with its flow rates. You simply need to store water for certain customers’ requirements.

Storage gas fired water heaters with an inbuilt 150 lire stainless steel hot water tank energy efficient hot water heater from Flexiheat UK

Storage option – 28kW or 34KW output options

The “SFKA” range, as they are designated, is available in natural mains gas or as LPG as their fuel source and is available with an output of either 28kW or alternatively a 34kw output model.

They come complete with a 150 litre stainless steel storage tank, which has a long warranty, and all the associated plumbing pipework and a pump local within the casing.

internal picture of our hot water heater with storage tank which is gas fired from Flexiheat UK

SFKA 28 or 34 KW Output models – Natural gas or LPG powered

They also have easy access for service or to maintain this reliable water heater unit as the panels are removable-with loads of room to get at and checkout the plumbing components that connect the heat exchanger of the water heater to the storage tank.

Thermal efficiency

In any domestic or commercial hot water heating system, any gas fired water heaters used these days must not only be a reliable appliance but also as efficient as possible.

This is where condensing water heaters come in as a solution with regards to gas fired water heaters, as you can recover the latent heat from the heater’s flue gases and recover that energy via a heat exchanger back into the hot water temperature-and not lost to the flue gases and the environment whilst saving the customer money.

Gas fired water heaters in condensing mode as it extracts all the energy from the fuel

Gas fired water heaters – Because the flue gases leaving the water heater are cool, they form a visible mist or plume of water vapour whilst leaving the flue terminal point or location


Because of this condensing process, our condensing gas water heater range are at least 15% more efficient than non-condensing systems. With the current high cost of energy, any customer may save significantly on their water heating costs by the installation of a water heater that will condense, whether in a domestic or commercial application.

ErP A rated gas fired hot water heaters - contact Flexiheat - picture shows energy efficiency sign so the customer can make an informed decision

Thermal efficiency or energy efficient ErP rating – “A”


This type of water heater is ErP “A” rated-and due to recent legislation changes, you must now fit condensing gas fired water heaters in all new and retrofit commercial water heating systems. Please visit this location on our site for more in-depth information on this- Water heater legislation changes-Part L Building Regulations-June 2022

Gas water heater controls

You can use the thermostat built into the control panel on the device to set the hot water temperature output required, or alternatively, we do a remote temperature controller option too.

If you require any more suitable support, solution advice, check stock, delivery times or require a price on our gas water heater range from Flexiheat UK, then please use the contact us form page on the website, or alternatively feel free to give us a call on 01202 822221, as we sell direct to the trade (speak to us regarding a trade account) and public customer base. Connect with us on Facebook or Twitter so you can contact us at any time.

Commercial Hot Water Cylinders or Calorifiers

Commercial hot water cylinders or cylinder unvented or vented indirect water heaters 200 to 6000 Litres Flexiheat UK

Commercial domestic hot water cylinders or calorifiers from 200 to 6,000 Litres

Commercial hot water cylinders are designed to satisfy substantial or continuous hot water demands such as hotels, care homes, schools, hospitals, camp sites, sports centres, residential or office blocks, when there’s a frequent requirement for large quantities of domestic hot water, in a short period of time, without any performance losses, when staff, residents or visitors create demand for warm water.

Our commercial cylinders, tanks or commercial calorifiers as they are also known, provide a solution for large scale commercial domestic hot water capacity, with fast flow rates that satisfy even the toughest of demand requirements.

Commercial cylinders for commercial water heating

Commercial cylinders come in various options and can use various technology, such as solar (renewable heat energy), electricity, heat pumps or warm water thermal systems (again a renewable heat energy source) to power the domestic hot water cylinder. The two leading hot water cylinder water heating solutions or options are-

Indirect – indirect commercial cylinders / calorifiers

Indirect commercial cylinders showing the coil which is used to heat up the DHW via a boiler, heat pump or solar heating system which transfers the heat to the water heating system

Indirect commercial cylinders – Showing the internal hot water heating coil

These are a storage commercial hot water cylinder, that are often powered by a traditional heating boiler that supplies the system, via a coil (which can be a single or double coil) or even a plate-to-plate heat exchanger for high warm water capacity solutions.

The cylinders, tanks or vessels storage capacity can be from 200 litres up to 6,000 litres in system capacity, (any cylinders under 200 litres we classify as domestic sizes – but there is no hard and fast rule on this) although bespoke designed models can be produced to support any larger specific requirements you may have.

Factors such as available installation space, may come into consideration and it is possible to link up several smaller cylinders or buffer vessels to meet the required storage capacity

Our indirect commercial hot water cylinder range can be fitted with an electrical immersion heater or heaters, as a back up to your primary heating energy source such as a boiler, thus direct heating of the water.

Direct – Direct commercial cylinders or Calorifiers

A direct commercial hot water cylinder is a unit that uses a heat or energy source that is physically located within the cylinder, normally this is an electric immersion heater or multiple immersion heaters, to warm the water – thus the term “direct water cylinder”. Normally the require three phase electric power rather than single phase supply service, as any immersion heater over 3kW requires a three-phase power supply. The immersion heaters have a control thermostat, that allows you to set your desired temperature.

Often used in in premises or a property where there is no access to gas or oil, or more commonly with businesses or individuals who are using a renewable electric supply or buying electric that is produced by certified renewable sources – enabling them to have a carbon neutral heated system.

We have a dedicated webpage on our direct commercial cylinders, which are stainless steel cylinders on our website here –

Commercial Direct Electric Water Heaters

Materials of construction of hot water commercial cylinders

There are two main options for the construction of the vessels themselves – being


Vitreous enamelled coated steel vessels

Vitreous enamel protects materials from corrosion. Due to its ability to interact molecularly with the steel surface of the tank, it can store DHW at the highest temperature of 95 ºC  without breaking down or coming off from the steel surface of the tank. All internal linings in DHW cylinders must, by law, be “food grade” (EC Regulation 1935/2004). Our vitreous enamel has food grade certification at the specified test temperature according to current regulations at 120ºC, which guarantees its maximum quality at extreme working temperatures, and is suitable and approved for potable water use.

Ultimately vitreous enamelling is a food-grade, impermeable coating with a porcelain appearance that protects the storage tank’s metal surface when it comes into contact with domestic water.

The range has evolved to the point that enamelled lined commercial cylinders now have the same working pressure of 8 Bar or even 10 Bar pressure (at special request) as their suitable stainless steel equivalents, but at reduced costs.

The other benefits are that they are more cost effective than a stainless steel vessels / stainless steel cylinders or buffer vessels range. The warranty period on this range is 5 years.

high performance indirect hot water heaters calorifiers 200 to 1000 Litres

high performance indirect domestic hot water calorifiers / cylinders 200 to 1,000 Litres

Technical details of the domestic hot water heaters

High performance hot water calorifiers or water heaters cylinder that come with a warranty details - Flexiheat UK

200 – 1000 Litre Calorifiers – The HLB option have a 400mm inspection and clean out manhole on the 800 litre and 1,000 Litre hot water storage models


commercial cylinders water heating performance from Flexiheat UK trading in England UK

Based on a primary inlet heating temperature of 85C


Continuous hot water flow rates at various input temperatures for 10C to 45C


Warm water production flow rates from 10C to 45C for our commercial cylinders or buffer vessels


Continuous hot water flow rates at various input temperatures from 10C to 60C


Warm water production flow rates from 10C to 60C for our commercial cylinders or buffer vessels


Cathodic protection should be installed in all DHW tanks composed of carbon steel with an inner lining to DIN 4753. A cathodic protection system consisting of sacrificial magnesium anodes and an anode charge metre is included as standard with this  tank series.

Cathodic protection systems with sacrificial anodes must be monitored for wear on a regular basis and replaced, if necessary. You can upgrade to the special electrically powered titanium anodes that emit the necessary current for protection of the tank lining which means that, unlike sacrificial anodes, there is no wear and the anodes do not need to be replaced.

Industrial Hot Water cylinders – from 1,500 to 6,000 Litres 

Details on the 1,500 litre to 6,000 Litre Industrial hot water cylinders / Water heaters

Industrial hot water cylinders water heaters from Flexiheat UK

Industrial hot water cylinders water heaters from Flexiheat UK – 1,500 Litres to 6,000 Litres


Technical details

Industrial hot water cylinders technical data from 1500 to 6000 Litres - Flexiheat UK

Download the Domestic hot water cylinders and storage vitreous enamelled units brochure from Flexiheat UK


Stainless steel cylinders

Stainless steel cylinders – This material has become popular over the years, as stainless steel has a much higher resistance to all forms of corrosion, including stress and crevice, making it highly durable and promising a longer working lifespan of the commercial cylinder.

Stainless Steel also can withstand extremely high pressure, which has paved the way for the unvented hot water cylinders that we see today. Unvented commercial cylinders have grown in demand due to their delivery of mains pressure hot water services.

These two factors have made this high-quality material the perfect solution for pressurised domestic water heating services.

We also do a range of stainless steel buffer vessels too- Buffer vessels are used to store hot water either hot water for heating or how water for domestic hot water use -these are detailed on our dedicated buffer vessel webpage – look for the stainless steel options

Commercial unvented hot water cylinders

Unvented cylinders – provide mains pressure water directly from the cold-water mains. The cold water is directly drawn from the mains water supply, then heated by the relevant heat source that you supply to the commercial cylinders

When using electric as your fuel to power the water cylinder they are referred to as – direct commercial cylinders unvented.

Or when powered by boilers which can be either gas or oil boilers, or even heat pumps these days – they are referred to as an indirect commercial cylinders unvented.

Benefits of an unvented hot water system for commercial premises

• Maintain strong pressure thanks to direct mains supply – in that direct mains supply can have a pressure up to 10 Bar

• No cold-water feed and expansion tank (also referred to as the header tank) at high level – that would give the system pressure, is required

• Thus, an unvented cylinder doesn’t rely on gravity fill and be fitted in any location

• Enhanced hygiene quality and safety – a sealed system not only eliminates the risk of leaks or freezing of the header tank in colder conditions, also contamination of the tank is also removed.

Fast recovery commercial hot water cylinder?

We often get asked what are the fastest recovering commercial cylinders – and the answer is – Our tank in tank commercial hot water cylinder range -which are ideal for a property or premises with high demands.

Commercial calorifiers

We have some of the best commercial hot water cylinder’s on the market, all designed to the highest quality standards, and with all the relevant safety features. All of our commercial hot water cylinder is approved to the PED (Pressure Equipment Directive) and the approved Energy Related Products (ERP) Directive 2009/125/CE, where applicable.

Should you interest and require any more support, free design or selection advice or costs/ get a quote on our commercial hot water cylinder range then please use the contact us form page on the website, or feel free to give us a call on 01202 822221, as we sell direct to the trade and public.

Commercial Boilers

commercial boilers wall hung for heating Flexiheat UK

Gas condensing boilers for commercial boiler installations

Commercial boilers are manufactured to fulfil the special needs of commercial premises or businesses or for heating apartment buildings with heat interface units, via a local heating network. Commercial boilers work similarly to domestic boilers, but they generate a larger heat output, making them suitable for commercial boiler installations.

Whether you are a professional heating engineer or a business owner looking to upgrade your boiler, this introduction about boilers with high energy-efficiency for commercial or even industrial heating will show you your options.

Our commercial boiler range has been designed and developed to meet a wide range of applications and project requirements from heating commercial stores, factories, schools, hotels, pubs, and leisure industry – just to name a few commercial heating applications with condensing technology to achieve the energy savings.

Commercial boiler systems

They are ideal boilers or perfect solution for producing domestic hot water as well as doing the heating system in a commercial property. This is achieved by using a boiler or even boilers in conjunction with suitable indirect hot water heaters or heat interface units. Making them a system boiler in this case.

Wall hung boilers

commercial gas boilers that are wall hung condensing devices from Flexiheat UK

Gas boilers – wall hung boilers with condensing technology for commercial heating

Wall hung gas condensing boilers are the most popular units these days for commercial buildings – especially in reference to commercial gas boilers, as they are the ideal boilers to fit in relatively small boiler houses and are easy to cascade to suit any project.


Commercial gas boilers in cascade offer higher modulation ratios, and when you bear in mind that commercial boilers spend 70% of their time at 30% of heat output, and the other 30% of their time at full output range, commercial gas boilers that have a high modulation ratio support these demand cycles.

The result is longer run times with lower cycle rates as the boiler controller operates the required number of commercial boilers or boiler to meet the heating demand of the system, which also reduces the wear and tear on boiler installation as continually cycling on and off can result in early failure of gas valves, fans and pumps fitted to the boiler or heating system.

We supply a full range of high efficiency commercial gas boilers, with modulation figures for single piece boilers of 1:20 and when used in cascade, with a maximum kW output of 960kW, so we can cover or fill any industrial or industry heating requirement as well as commercial applications.

Commercial floor standing boilers are still a very popular installation in the UK, floor mounted boilers are available as gas fired either natural gas or as an LPG condensing boiler , electric or oil fired condensing boiler ranges with some very large outputs.

Commercial floor standing boilers

Commercial floor standing boilers or free standing boilers are still a very popular installation in the UK for commercial applications, floor standing boilers are available as gas fired either natural gas or LPG, electric or oil-fired ranges with some very large outputs. There are various subject options –

gas-fired floor mounted boiler range

industrial gas boilers for heating Flexiheat UK

Gas condensing commercial and industrial range – stainless steel heat exchangers

Our gas fired floor mounted commercial gas boiler range is detailed more on the following webpage – commercial and industrial gas fired floor mounted boilers – which you can install up to 12,160 kW of heating power – which is a large amount of heat ! and enough to cover any installation requirements from one of the leading brands of gas condensing boilers for industry or commercial applications.

Oil fired floor standing commercial / industrial heating boilers

commercial and industrial floor standing condensing oil boiler also available as a dual fuel commercial boiler - oil and gas

Also available as a dual fuel commercial boiler – oil and gas fired

Commercial oil fired boilers, that are floor standing start at 70kW and go all the way up to 1,550 kW in condensing oil fired boilers – the UK and European legislation states that all boilers from 70kW to 400kW must be condensing to meet the Energy Related Products Directive requirements for heating systems for commercial premises. See this webpage for more information on our commercial floor mounted oil boiler range.

But it would be foolish not to use condensing above the stipulated 400kW, as a condensing unit is 20% more efficient than a non-condensing boiler. Again, they can produce domestic hot water through any brand indirect cylinders or heat interface units.

Frequently asked questions

Here’s some frequent questions we get

What are commercial boilers?

Commercial boilers are widely used to heat structures such as offices, schools, blocks of flats, and local surgeries or hospitals etc. They typically create hot water using either gas, electricity, or oil as a fuel source. This heated water is used to power the heat emitters in the building, such as underfloor heating, radiators, or fan coil units.

What size is a commercial boiler?

Gas and oil-fired commercial boiler range in size from 70kW to 2,000 kW plus. This wide range of output capacities helps to guarantee that businesses may select products that fit their individual heating and hot water requirements.

Commercial boiler prices UK

If you require any further support, advice, latest offers of our commercial boilers range, be they floor standing or wall hung models then, please contact us via our email contact form above on the website or call our business sales services team direct on 01202 822221 and deal with your commercial project interest. Sign up and follow us on Facebook and twitter for our latest news.


Calorifiers or water heaters from Flexiheat UK

What are calorifiers?


Calorifiers are indirect-fired water heaters used in a heating and hot water system to provide domestic hot water. The term “indirect fired” refers to a water heater that does not have its own burner. It is a water storage cylinder with one or more heat exchanger coils containing hot liquids , normally water but can also be a solar fluid , or can be a tank in tank design of indirect hot water heaters.

The calorifier tank is designed to be connected to an external heat source, such as a gas boiler, an oil boiler, or a renewable energy system such as a heat pump, wood or pellet boiler, or an electric boiler.

The term calorifiers is used in the heating industry, and this is the area we are referring to. The term calorifiers is also used in the marine industry – a marine calorifier is a completely different to heating calorifiers as they are fed by engine coolant, that use drop coil technology.

External heat source

Generally, in the past calorifiers have been powered by a boiler heating water up to a temperature of normally 80C – this hot water is classified as the primary hot water which feeds a single coil normally fitted in lower half space or multiple coils (twin coil), within the water heaters tank.

Hot water calorifier showing the internal coil Flexiheat UK

Single coil shown inside the water heaters

The heat exchanger coils of the calorifier work by heating up the cold water in hot water cylinder to the required demand

The cold water contained in the water heater is then heated up to 60C to prevent the formation of legionella in the domestic hot water systems – this is known as the domestic hot water (commonly abbreviated to DHW)

Please note – You will require a calorifier with stainless coils if you have a central heating system with an aluminium heat exchanger or if there is any aluminium in the system. Galvanic corrosion, particularly the interaction of two dissimilar metals in water, will cause the calorifiers early demise.

For calorifier sizing, please see our webpage – commercial calorifier sizing

Click here – For our 80 to 500 litre indirect stainless steel calorifier range

Or for our 200 litre to 6,000 Litre commercial indirect hot water heaters  –  click here for our Commercial hot water cylinders

and here for our tank in tank water heaters – which are high recovery water heaters

Electric heater backup or top up

Calorifiers can also have a backup or top up system for heating water, in the form of an immersion heater.

The immersion heater is powered by electricity, and in the case of heating boiler failure or when heat pumps can’t heat the water heaters to the desired temperature (normally the maximum is 55C that a heat pump can produce – remember we require at least 60C) then they, by efficient means (electric has 100% efficiency) , either replaces the function of the heating coil to heat the potable hot water directly or additionally to the heat generated by the coil in the case of heat pump’s, tops up the hot water heating demand.

Hot Water

Commercial buildings, the leisure industry and public buildings domestic hot water systems are fed by water heater calorifiers normally on a DHW secondary return system to ensure the hot water system is heated and maintained above the temperature required to prevent the risk of legionella’s disease.

This guarantees that hot water is always accessible at any of the taps, regardless of their proximity to the calorifiers.

Hot water cylinder temperature control

All calorifiers require a thermostat to control the operation of the heat source supplying the water heater.

Domestic hot water calorifier

If you require any further assistance, latest offers / cost of our calorifiers range, which are indirect hot water cylinders / , please contact us via our email contact form /page above or call our sales team direct on 01202 822221.