Commercial Hot Water Cylinders or Calorifiers

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 domestic hot water demands such as hotels, care homes, schools, hospitals, camp sites, sports centres, leisure 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 in commercial properties or commercial buildings.

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.

This commercial cylinder range can be used as a vented (for vented applications we highly recommend the stainless-steel option – due to the fact air ingress is more prevalent in vented DHW heating systems – as stainless has the best longevity) or unvented cylinders (we just need to add a domestic hot water unvented kit to the unit)

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 commercial cylinder 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 stored hot water capacity can be from 200 litres up to 6,000 litres in system capacity, (any cylinders under 200 litres of stored hot water 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 specific requirements your commercial project 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 for commercial buildings.

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 in the commercial cylinder.

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 commercial properties or a commercial project 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 domestic hot water 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 mild steel vessels

Vitreous enamel protects the mild steel from corrosion. Due to its ability to interact molecularly with the mild steel surface of the tank, it can store domestic hot water at the highest temperature of 95 ºC  without breaking down or coming off from the steel surface of the tank. All internal linings in domestic hot water commercial 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 the stored hot water.

The range has evolved to the point that enamelled lined commercial cylinders now have the same working pressure of 8 Bar for the domestic hot water 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

The cylinder hot water performance is directly related to the coil primary input temperature and the water flow rate to the coil as per the below data table.

Most of our commercial cylinders can handle more than 6M3/hour of flow, but please check with us as the pressure drop through the coil increases to the point that it may be impractical for real world use.


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

We do a full range of commercial gas boilers to power this commercial hot water cylinder range – these are detailed here – Commercial gas boilers – floor standing, or wall hung.

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.

Stainless steel commercial indirect hot water calorifiers from Flexiheat UK

Stainless steel commercial hot water cylinder range from 200 to 1000 Litres.


DHW Performance data for the above S/S range

For 10C to 60C DHW heating

GX200-HL to GX1000-HLB commercial indirect water heater 10C to 60C technical table Flexiheat UK

10C to 60C Hot water production performance tables


and for 10C to 45C DHW heating

GX-200-HL to GX-1000-HLB commercial indirect water heater 10C to 45C technical table Flexiheat UK

10C to 45C Hot water production performance tables


For full output data on our  s/s commercial cylinders – please see pages 30 & 31 of the following brochure –

Download the Stainless Steel cylinders for domestic hot water production and storage brochure – Flexiheat UK


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 coil of 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 for reduced running costs – 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 – This commercial cylinder range is -which are ideal for commercial properties 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 cylinders are 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,to talk to our experts today as we sell direct to the trade and public.