Gas hot water tank or cylinder

A gas hot water tank also known as a gas hot water cylinder are gas fired water heaters that are storage hot water heaters.

gas hot water tank or gas fired hot water cylinder from Flexiheat UK;water heaters gas

These gas water heaters tend to be used in commercial or heavy domestic applications where people want a domestic water heating device that utilizes a hot water storage tank to optimize water heating capacity and supply hot water instantly.

Water heater applications

Typical applications for this range of gas fired water heaters is smaller health centres, hairdresser saloons, pubs and leisure facilities, smaller hotels and bed and breakfast establishments or properties, where hot water demand and good flow rates are essential, and they have a gas supply – either natural mains gas or LPG (liquefied petroleum gas).

These gas water heaters allow you to sperate your central heating system from your domestic hot water system, meaning you can achieve greater energy efficiency by only heating water in the summer months and reduce your energy bills or your customers for their water heating.

Gas fired water heaters

This gas condensing water heaters range is designed to store 150 litres of domestic quality hot water at a hot water temperature of 60C or above in the hot water cylinder, this instant hot water is then available to the installation when there’s a demand from the showers, baths, or hot water taps, with good flow rates.

gas hot water cylinder internal picture showing the storage tank with with high thermal efficiency, tankless gas water heater

Internal picture of our storage gas water heaters

We do two main types or models, a 28kW gas water heater or a 34kW gas water heater –

Our reliable 28 kW output gas-fired hot water tank with its 150-litre stainless steel hot water cylinder (storage tank) will provide a continuous D.H.W. supply at a 30°C temperature rise of mixed water with a first 10-minute flow of 305 litres and a 1-hour flow rate of 984 litres.


Our reliable 34 kW output gas-fired hot water tank with its 150-litre stainless steel hot water cylinder (storage tank) will provide a continuous D.H.W. supply at a 30°C temperature rise of mixed water with a first 10-minute flow of 333 litres and a 1-hour flow rate of 1,167 litres.

Condensing water heaters

As our gas fired water heaters range are condensing water heaters, you’re getting many benefits with a reliable and efficient hot water installation, with the benefit of lower energy consumption. They are as such hybrid water heaters, with a tankless water heater which are condensing water heaters combined with a storage tank.

Gas water heater features

Our commercial,or heavy domestic gas water heaters water range features

  • Our heat exchanger is produced in stainless steel and has large single-tube coils with a diameter of 28 mm. Because of this, it has very low pressure drops, which means it is less likely to get clogged, uses heat more efficiently, and is easier to clean.

High DHW performance gas fired water heaters

  • The domestic hot water temperature adjustment ranges from 40 °C to 60 °C
  • Anti-legionella system;
  • These are condensing water heaters
  • Possibility of recirculation or direct feed
  • Remote management and control of these gas fired water heaters is possible via 0-10 volts or via our Opentherm thermostat and controller with an app that allows you to control the gas water heater from a phone, tablet, or PC.
  • Integrated post-circulation for excess heat disposal to help save energy.
  • Self-diagnostic electronic board with frost protection
  • Integrated recirculation function for immediate DHW delivery;
  • Fast H2O pre-heating for efficient and instant DHW dispensing without waiting.
  • Electrical systems protection level is IPX5D
  • Very low NOx emissions, maximum 50 mg/kWh.
  • Suitable Anode to protect the storage tank.
  • Available in natural gas (mains gas) or LPG
  • Can even be used in industrial applications for decentralised water heating

Dimensions of our water heaters gas fired

Both water heaters gas fired have the same dimensions occupying a small space or footprint.

Gas hot water cylinder dimensions for SFKA28 and SFKA34 models from Flexiheat UK

Contact us

Whether you a new customer or a trade account, should you require anymore assistance, information, check stock or get a recommended price / cost on the best gas hot water tank or gas fired hot water cylinder in natural gas or LPG on the UK market with fast delivery times, please contact our customer services sales team on 01202 822221 or use our email contact above on the web page for our email form.

35kW Combi boiler – Combination boilers

35kw combi boiler - a high efficiency combination boiler for central heating and hot water being a condensing boiler with a long warranty. No hot water cylinder is required as your producing domestic hot water on demand.

35kW combi boiler – R2C34 From Flexiheat UK – high performance hot water flow rate of 16 litres/min with a 30C temperature rise

Our modern 35kw combi boiler employs condensing technology to effectively heat the system water by removing latent heat from the flue gases which enables these boilers to have a “A” ErP rating for space heating efficiency and “A” ErP water heating efficiency rating, which means higher efficiency and thus lower running costs for this combination boiler.

A combination boiler is the most popular boiler type in the UK, as the size of a combi boiler is one of its main benefits. As Combi boilers do not require external hot water cylinders / water storage cylinder, this type of boiler provides both hot water and central heating in a single compact unit for more than one bathroom properties.

Having “heating and hot water” in one boiler has many benefits and will save installation space on site and the users or customers will have a lower installation cost as a combination boiler installation is quicker that a system boiler and indirect cylinder installation.

Our gas boiler has a great modulation or turn down ration of almost 10:1 in range, which means the boiler will match or address the central heating load requirement very closely.

With low noise level, this reliable gas boiler, which is available to natural gas or propane gas (LPG) will produce 16 litres/min with a temperature rise of 30C of domestic warm water and is up to 108.6 % efficient.

35kW Combi Boilers

A gas burner in the combi boiler is lit when you need hot water or heating. The primary circuit receives the heat from the burner through the main heat exchanger, where it is then either moved straight to the radiators or through a plate heat exchanger to your hot water taps in larger homes.

One of the key features of our 35 kw ErP compliant modern combi boilers is a “pre-heat” system, which enables the boiler to contain a small volume of water that can be used instantly. The water is kept in the boiler all day and kept at the desired temperature so that it can be quickly delivered to the hot water taps.

Fuel options for our 35kw boiler combi

This 35kw combi boiler is available in either natural gas or LPG (propane) gas options depending on local availability of the fuel to the property or house. Should you ever need to change your gas type, just speak to our customer services as we can supply a gas adaptor kit to change the gas boiler to your required fuel type. This is an easy installation and takes less than quarter of an hour to do at most if ever needed.

Stainless steel heat exchangers in our combination boiler

All of our condensing boilers range use stainless steel heat exchangers because of their high corrosion resistance across a broad pH range. Your 35kw combi boiler will last longer as a result and has a long warranty period.

When discussing our combi boilers dependability, the development of our modern new design heat exchanger from one single continuous coil permits the water to move through more quickly, efficiently, and at a higher flow rate performance.

This reduces the possibility of debris blockages, increasing reliability and lengthening the boiler’s lifespan. A Stainless steel heat exchanger construction will withstand high flow rates without corroding or wearing out.

Patented A rated ErP water heating efficiency

Inside the high performance patented stainless steel main heat exchanger is a 12mm diameter internal stainless steel pipe that produces domestic hot water (installed within the 28 mm diameter heating exchanger). This ensures you have a quantity (approximately 7 litres) of “warm water ready to go,” as they say. Its total length is 8 metres. Because these combi boilers produce domestic hot water by continuously condensing, which makes them very efficient, gas energy costs and bills are reduced.

Pipe in pipe stainless steel heat exchanger for heating and hot water production for our 35kW combination boiler


Additionally, these design features reduce the possibility of scale accumulation, which you can expect in older combi boilers with a plate heat exchanger that many companies still use.

Blocked combi heat exchanger with scale and debris

In areas with hard water, this is crucial because our heat exchanger’s high velocity and flexing while in use reduce the potential for scale to build up and prevent it from happening, helping to ensure a long life, trouble-free operation, and a good hot water flow rate.

Good mains water pressure is needed for combi boilers

One potential drawback of a combi boiler is that if multiple showers and taps are initiated simultaneously due to combi boilers pulling water directly from the local availability in the mains cold water supply, the water pressure can drop quickly for example.

Our boiler needs a minimum water pressure of 0.5 Bar and will operate up to a maximum water pressure of 6 Bar. For good hot water performance we recommend around 3 Bar water pressure for your hot water system.

Boiler specifications, features and details

Our 35kw combi boiler (35 kilowatts power) has both “A” rated ErP water heating efficiency performance for both heating and domestic hot water, with low noise level outputs.

This 35 kw boiler range is suited for space heating or central heating with radiators or underfloor heating systems with a high efficiency of 106.43% when used on a 50/30C range flow and return system which will save you money and cost on your gas energy requirements.

With a useful central heating output of 36.19 kW when used on a 50/30C system , or when used on a 80/60C system the central heating output is 33.35 kW

R2C34 combi boiler 34kW technical data, showing the central heating or space heating and domestic hot water performance of this condensing boiler by Flexiheat UK

Download the Flexiheat R2C 34kW Combi Boiler Manual

For larger homes, or homes that have larger warm water demands then please look at our next size up combi boiler our – 50kW gas combi boiler


Our 35 kw combi boiler dimension are – Height = 642 mm , Width = 410 mm  and a Depth of 350 mm – with a weight of 44 kg making these robust units easy to fit in any installation.

combi boiler 35kw dimensions Flexiheat UK

Flow and return and gas connections – 20 mm

Hot and Cold water connections – 15 mm

Flue lengths and options

With extensive flue options of up to 60 metres in length – when using a sperate 80mm diameter twin flue system, or up to 10 metres in length when using our 80/125mm co-axial horizontal flue system option – both options make this 35kw combi boiler a room sealed gas appliance.

Horizontal flue kit co-axial room sealed for our boilers Flexiheat UK

Horizontal flue kit co-axial – the 80/125mm Ø will go 10 metres


Or our vertical flue option

Vertical flue kit co-axial for our boilers Flexiheat UK

Vertical flue kit co-axial – the 80/125mm Ø will go 10 metres vertical

Control options

This boiler can be controlled via the inbuilt digital display, or you can opt for our smart thermostat range option, which is an OpenTherm control system, that allows you to control these combi boilers from an app on your phone, tablet, or computer.

cloud warm app to control the boiler from your mobile phone or tablet

Cloud Warm App – control on the go !

Nest and Hive controllers are Opentherm compatible, so you can use them with what we consider the best 35kw combi boiler on the market.

Common question

35kw combi boiler how many radiators can it run ?

The average size radiator in a new build property is now 1.5 kW (kilowatts) output – so your looking at 23 radiators, but for older properties your looking at around 11-15 radiators on average for this size gas boiler type.

Please ensure that the local area boiler installer or a company engineers are gas safe registered and can provide a labour warranty and service agreement on the install.

Delivery or Collection

You can collect for free from our location – postcode BH21 6SZ – just please phone ahead to check stock levels or alternatively we deliver on a small pallet service to prevent any risk of damage, throughout mainland UK and Northern Ireland ,just quote your postcode for the price of this service.

Contact us for free boiler quotes for your combi boiler requirements

Should you require anymore assistance, information or prices on the best 35kw combi boiler in natural gas or LPG gas on the UK market, please contact our customer services sales team on 01202 822221 or use our email contact above on the web page for our email contact form. All of sales are supplied with a vat invoice.

24KW Combi Boiler – Combination boiler


24kw gas fired combination boiler - condensing - model R2C24 from Flexiheat UK

A 24 kW combi boiler is an ideal new boiler that is suitable for a small one-bedroom home, apartments or flats.

Because there isn’t much space to heat in these-sized properties, there are normally fewer than ten radiators (the average size of radiators in a new build property is 1.5 kW). There is also less demand for domestic hot water in the property because they frequently have a shower or a single bath that can’t be used simultaneously.

Our 24 kW combi boiler is a small boiler that provides both heating and hot water on demand. With its compact dimensions, it is designed to fit into a standard 350mm deep kitchen cupboard unit and has a low lift weight, which makes them the right combi boiler for these types of properties.

These combi boilers are are available in natural gas or LPG ( propane) gas and

This gas boiler has an ErP rating of : Water heating efficiency “A” and a space heating efficiency “A”  – thus reducing energy usage.

Instant warm water on demand

The instant hot water system, provides energy efficient hot water to the taps or bathroom, and that’s why the Energy Saving Trust recommends a high efficiency combi boiler, when installing a new heating system or to replace an existing non condensing combi boiler in your flat or smaller property.

Larger properties, with more bathrooms will have a higher demand for instant water , and require a larger boiler size to achieve the local availability of warm water to the taps or showers through the home – as a boiler guide we do a 35kW combi boiler ( typically to suit a 3 bed home for example) and a 50kw combi boiler suited or capable of doing 4 or 5 bedroom property depending on related factors such as available mains water flow rate to the home. The 50kW combi boiler version has its own dedicated webpage, that shows all its features and performance data here : 50kW combi boiler

High efficiency combi boiler

All boiler manufacturers have since 2005 , have had to make a high efficiency combi boiler which is condensing in operation to help reduce carbon emissions via the combi boilers lower carbon-footprint. It has been mandatory to instal condensing boilers, whether they are combi boilers or system model boilers.

Our easy-to-use combi boiler is “A” rated for both heating and hot water, making it a high-efficiency combi boiler.

Hot water heat exchanger

The 12mm diameter internal stainless-steel pipe where domestic hot water is produced, is inside the patented stainless steel main heat exchanger (28mm diameter). Its total length is 8 meters, and this ensures you have a volume (approximately 6 Litres) of “warm water ready to go” as they say. The DHW production is always available and always in condensing operation, resulting in lower energy costs and bills for these combi boilers.

combi heat exchanger stainless steel with large water ways to prevent blocking

Stainless Steel heat exchanger with large water ways to prevent blocking

This design feature also reduces the chance of scale, something that older technology combi boilers that use a plate heat exchanger can suffer from. This is incredibly important in hard water areas– as our heat exchanger, with its high velocity and flexing in operation, reduces the ability for scale to build up, and prevents this happening ensuring a long life 24kw combi with trouble free operation and a good hot water flow rate.

Scale blocking the heat exchanger - older technology heat exchanger systems for DHW production

Scale blocking the heat exchanger – older technology heat exchanger systems for DHW production

This unique and clever engineered solution for our heat exchanger system provides many advantages as opposed to most boiler manufacturers that use a traditional separate plate heat exchanger system, for the domestic water. This why many consider our 24 kW combi boiler the best combination boiler on the market in the UK, with high reliability at a fair market price or cost.

Central heating system or space heating of the combination boiler

A combi boiler provides warm water for radiators or an underfloor central heating system or any other type of space heating, with our compact 24kw combi model having a hot water (DHW) priory system. The total heat requirement (radiators ,underfloor heating etc) should not exceed 24.79 kW based on a 50/30C flow and return heating when in operation on the coldest of days for this boiler size.

Specifications of the R2C24 combi boiler 24 kW condensing boiler

The models comparison of technical data, is covered in the picture below.

R2C24 combination boiler - natural gas or LPG gas - technical data Flexiheat UK

Hot water flow rate -11.5 Litres/minute in typical winter time – when you need warm water the most !


and in more detail in the manufacturer manual – which can be downloaded here –

Download the Flexiheat R2C 24kW Combi Boiler Manual


Our 24 kilowatts output dimension details are generally – Height = 642 mm , Width = 410 mm  and a Depth of 307 mm –  making the units easy to fit in any installation.


R2C24 24kw combi dimensions - natural gas or Lpg fuel options

24kW Combination boilers with high modulation

Our combi boilers have an exceptionally high modulation range or ratio of 1:9 for this size boiler, which means our 24kw combination boiler will ramp all the way down to 2.9 kW of heat output. This high modulation range ensures the closest of heat load matching to the properties demand, which results in lower heating energy bills.

Frost protection

These combi boilers fire up when the water temperature drops below 5 °C within the heat exchanger, automatically starting the burner until the heating water reaches the temperature range of 30 °C. This anti-freeze system will protect the boiler up to an external temperature of -10 °C.

Flue lengths and options

With extensive flue options of up to 60 metres in flue length – when using a sperate 80mm diameter twin flue system, or up to 10 metres in length when using our 60/100mm or 12 metres for our 80/125mm co-axial horizontal flue system option – Both systems make these combi boilers a room sealed gas appliance.

Horizontal flue kit co-axial room sealed for our boilers Flexiheat UK

Horizontal flue kit co-axial – 60/100mm Ø will go 10 metres , or the 80/125mm Ø option will go 12 metres

Or our vertical flue options

Vertical flue kit co-axial for our boilers Flexiheat UK

Vertical flue kit co-axial – 60/100mm Ø will go 10 metres , or the 80/125mm Ø option if your require more height – will go 12 metres

Control options

All our boiler sizes, be they the 24kW, 28kW or 35kW outputs or models can be controlled via the inbuilt digital display or you can opt for our smart thermostat range option, which is an open-therm control system, which allows you to control these combi boilers from an app on your phone, tablet, or computer.

cloud warm app to control the boiler from your mobile phone or tablet

Cloud Warm App – control on the go !

Nest and Hive controllers are Opentherm compatible, so you can use these with what we consider the best boiler on the market.

An Open-therm thermostat controller is a smart controller which helps your central heating run in an more energy-efficient state, as they can optimize and weather compensate the heating systems to the external weather conditions – Explained very well in the following video –


Condensing boiler installation

As gas safe heating engineer installer, normally with local availability must be used to ensure a safe installation ( always check their company registration number with the gas safe register) and to provide a labour warranty on the 24kw combination boiler install.

Contact us

Our 24kw combi boiler model are the ideal boilers for a smaller house, apartment or flat, with its compact dimensions this size boiler can fit in a kitchen cupboard if so required. Should you require anymore assistance, information or price on the best small combi boiler  in natural gas or LPG on the UK market, please contact our sales team on 01202 822221 or use our email contact above on the web page for our email contact form. All of sales are supplied with a vat invoice.

LPHW Unit Heaters

LPHW Unit Heaters- an air heater for a heating hot water system which can be powered by renewable sources of energy such as an air source heat pump, ground source heat pumps or a traditional hot water boiler from Flexiheat UK

LPHW heater range from Flexiheat UK

A LPHW (which donates Low Pressure Hot Water) heater is fed by a hot water system. A boiler, which can be a gas or oil boiler, biomass boilers or a heat pump, is the external warm water heat source used by these water heaters. The warm water is transported to the LPWH unit heaters by the heat source. Then a fan disperses the warm air throughout the area being heated, such as exhibition halls, production lines, sports halls , warehouses, garages and many other commercial or industrial buildings that require heating.

LPHW heater

In gravity feed systems, the flow and return pipework pressures for LPHW are frequently less than one bar in operation and 2 to 4 Bar in pressurised heating systems.

Our lphw unit heaters can operate up to a maximum pressure of 16 Bar with various discharge options – either downward discharge (vertical installation) or horizontal discharge units.

We also do an air heater version especially for a heat pump system, that has a larger delta T flow and return system, that these heat source systems can operate on.

Warm air flow

This cost effective water fed unit heater range are fitted with a three speed energy efficient fan installed on every model. The fan motor speed is controlled by optional control accessories, which range from a basic control option to a full BMS (Building Management System) compatible control model, which is frequently required and suited to commercial and industrial warehouses.


All of our manufactured controllers have temperature control, to turn off the air heater or heaters when they reach a certain temperature, or to modulate the fan motor on the units as required.

Product Construction

Because it is specially developed and made of expanded polypropylene, it weighs up to five times less than a conventional steel cased unit heater at the larger heat output sizes. This makes installation of the fan coil unit space heater easy even in tight space configurations.

Both these accessories make installing these heaters an easy task in warehouses or factories, especially when a unit heater mounting position may be required directly over production lines or to avoid pallet racking, etc.

Pallet racking in industrial warehouses

Heat exchanger

The heat exchanger in this extensive range of warm water heaters , made of copper with aluminium fins, ,which guarantees optimum heat output with high efficiency from the equipped heating coils. The air flow generated by the fan and motor is directed through the adjustable louvers fitted to the heaters into the rooms being heated.

hot water heat exchangers with aluminium fins for our warm air heater

The heat output of this extensive range of unit heaters for low pressure hot water systems is directly related to the heating hot water temperature, which is used to supply the unit heater or heaters.

Our units can work with a warm water medium temperature of 120 C and a maximum pressure of 16 Bar, so LPHW heating is not a problem for these units.

The fan speed of the unit heater, as well as the air throw of the model, influence the leaving air temperature and heat output of the unit heater.

We do steam heating models, which are listed on their own dedicated webpage here: steam unit heaters


Address all conceivable likely space configurations that require heating with two discharge options—horizontal or downward (installed hung from the ceiling).When air flow from a horizontal warm water unit heater might be impeded by obstacles in complex areas such as exhibition halls, downward discharge is especially well suited.

LPHW heater for directional heating with a downward discharge installation – we can accommodate all likely space configurations or complex areas

LPHW heater for directional heating with a downward discharge installation – we can accommodate all likely space configurations or complex areas

However, where directional heating is needed, horizontal discharge units with adjustable louvres are ideal and are the most popular installation configuration for this range of heaters.

Horizontal discharge units

The standard bracket supplied for the horizontal unit is an adjustable rotating console that allows for 170° rotation of the unit heaters and allows for directional heating as well as the adjustable louvers.

The bracket can also be used in a downward discharge from a ceiling installation, or we can provide other accessories like corner brackets that let the air unit heater be connected to the ceiling with threaded bar drop rods.

horizontal discharge units our LEO unit heaters water fed plastic EPP case;

Horizontal discharge units – our “Leo” unit heaters EPP Plastic cased from Flexiheat UK



500 Litre buffer tank or vessel

500 Litre buffer tank or vessel with energy class c insulation levels hot water storage for hydronic heating systems


Our 500 Litre buffer tank or 500 litre buffer vessel, is a hot water buffer tank normally used to store heating hot water or increase the heating system’s hot water volume. This energy is retained for later use and results in fewer but longer heating cycles for the heating system with our buffer tanks or accumulator tanks.

500l buffer tank for a heating system

This 500L buffer tank can be used on various heating systems, but is often used in conjunction with renewable heating systems such as biomass boilers or low carbon systems such as ground source heat pumps or air source heat pumps.

Air source heat pumps

For a heat pump to operate at peak efficiency, our buffer tank, also known as a buffer vessel, ensures minimal compressor run times and minimum water flow rates. For air source heat pumps, a buffer is necessary because it supplies the defrosting energy for the heat pump. If a heat pump is the only source of heating, it is also possible to integrate an electric immersion element to provide additional heating as needed to our multi port buffer tanks.

Specification of our buffer tank or vessel

Specification of our 500 Litre buffer vessel or 500l buffer tank

500 Litre buffer tank or vessel dimension details Flexiheat UK

Out 500L buffer vessel or tank – overall height 1,770 mm, overall diameter 850 mm with insulation – 650 mm diameter with insulation removed.

Tank storage capacity – 500 Litres

Height – 1,770 mm

Diameter with Insulation: 850 mm

Diameter without Insulations: 650 mm

Product insulation is polyurethane – 50 mm insulation

The insulation is removable – which allows you to get the buffer tank through a standard doorway access

Our 500l buffer tank is a great quality product at a great price

Buffer tank weight – 108 Kg when empty – 508 kg when full with hot water

8 x connection tapping’s – 40 mm (1 1/2″ ) female bsp – designated “KP” on the above drawing

4 x Thermometer or sensor pockets – 15 mm (1/2″) female bsp – designated “T” on the above drawing (sensor pockets are 1/2″ female threaded)

1 x Air vent eliminator or safety valve tapping or bsp safety connection – 40 mm (1 1/2″) female bsp- designated “OZ” on the above drawing

Full port dimensions off the floor for our FH16.500NB-O which is the 500 Litre model product is listed in the following data chart

500L buffer vessel dimensions all in mm Flexiheat UK

All dimensions are in mm for our buffer tanks

Buffer tank maximum working temperature – 95 Degrees Celsius

Buffer tank maximum working pressure – 3 Bar

With plenty of tapping’s this 500L buffer tank can be fitted with additional immersion heaters as a backup or top-up heat source.

This 500L buffer tank is manufactured from mild steel, so corrosion inhibitors must be used with this product.

Download the Flexiheat UK 400 to 600 Litre heating buffer tanks vessels brochure

Should you require another capacity or volume buffer tanks or a higher working pressure, then we do a full range of buffer tanks which are listed on their dedicated webpage.

Applications – hydronic heating systems

Our 500l buffer tank can be used with heat pumps, log fired boilers, gasification boilers, wood pellet boilers, or even traditional gas or oil boilers, Flexiheat UK offers a variety of multi-port buffer tanks and accumulator tanks.

Sizing criteria for a 500l buffer tank

Here are some guidelines on sizing for our 500L buffer tank

Air source heat pumps or ground source heat pumps: approximately 25 litres per kW of heat pump output (recommended by BS EN 14511 for defrosting of the heating system).

Wood pellet boilers: a minimum of 10 litres of tank volume for every 1 kW of boiler output.

Solid fuel boilers: a minimum of 30 litres of tank volume for every 1 kW of boiler output.

Wood chip boilers: a minimum of 12 litres of tank volume for every 1 kW of boiler output

Gasification boilers / log fired boilers: a minimum of 50 litres of tank volume for every 1 kW of boiler output.

Thermal storage tank or vessel 500 Litres capacity

If you require more product information, availability, technical support , check stock levels, delivery times or get prices on our 500 Litre buffer tank or vessel for heating hot water, then please don’t hesitate to get in touch. Contact our sales service team on 01202 822221 or use our email contact form via the contact tab above to message us. Connect with us on Facebook or Twitter for our latest products updates and special product price deals.

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

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

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 in hot water cylinders.

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 for vented cylinders.

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.