Thermal Store Cylinders

What is a Thermal Store Cylinder?

Thermal Store units are designed for efficiently storing large quantities of heat energy until it is required.

The thermal tank is filled with primary central heating water as opposed to potable hot water (tap water) which you will find in a conventional hot water cylinder.

Difference Between Thermal Store vs Hot Water Cylinder

The critical difference between a Thermal Store and a standard Hot Water Cylinder is that the Thermal Store provides hot water to your taps and showers, via a high surface area coil. This is also known as a heat exchanger.

High-pressure water from the cold main enters the bottom of this coil and absorbs heat from the surrounding water as it goes. When the water reaches the top of the coil, its temperature will have increased substantially, so it passes through a thermostatic mixer valve to ensure it’s delivered to your taps at a comfortable 55°C.

Assuming the store temperature is maintained at around 70°C, an unlimited amount of hot water will potentially be available.


Thermal Stores excel in versatility in that a variety of different connections and coils can be incorporated for whatever combination of heat sources and points of use you have.

Heating water can be extracted via coils and/or direct connections (depending on the pressurisation of these systems) and pumped around radiators and/or under-floor heating systems. This potentially allows the heating of the property to use any renewable heat sources that have been used to heat the store, as opposed to heat sources which use more expensive fuels.

For a full visual representation of the inner workings of a Thermal Store, please view the video above.

Thermal Stores are also available in combination type (in which the cold water expansion tank is combined into the top of the hot section), removing the need for an external header tank if space is restrictive.

If the installation space is too restrictive to accommodate a cylindrical Thermal Store or Thermal Store Combi, we also manufacture rectangular equivalents known as “CubeStores.” This alternative model allows for all the benefits of a thermal store whilst utilising the available space.

All thermal store units are supplied with immersion heaters, pressure-reducing valves, check valves, drain valves, expansion vessels, thermostatic mixer valves & float valves (combination model only). Optional extras such as control thermostats, temperature gauges, insulation upgrades, and metallic-silver cased finishes, are also available.

Example Specifications

These specifications demonstrate some of the example configurations of our Thermal Stores that can be mixed and matched to suit your unique requirements.

Direct Electric

The Direct Electric configuration is fitted with two immersion heater connections to allow for sufficient heat input, as well as being able to take advantage of Economy 7 Tariffs.

Immersion heaters continue to be a reliable, and now potentially renewable, heat source. Supplied by either mains electricity or solar PV panels, they can be used alongside other more powerful heat sources.

Indirect Boiler

The Indirect Boiler specification includes a 22mm boiler input coil allowing for heating with a conventional boiler. This can also be upgraded to a 28mm coil allowing for functioning on a Gravity system.

Gas/oil boilers are arguably the most reliable heat source for Thermal Stores, as they produce high flow temperatures, are fully controllable and don’t rely on warm weather. Their main drawback though is of course their use of fossil fuels, so using them as a supplement for at least one renewable heat source is worth considering.

The input of heat from a boiler can be via a coil or direct connections (depending on the pressurisation of the boiler system)

Solid Fuel

Solid fuel systems (Including Wood Burners, Biomass Boilers, Range Cookers, etc.) can be connected directly or indirectly to the body of water.

If these appliances are uncontrollable, high-limit stats or other temperature-limiting controls should be utilised to protect other components that can be damaged by prolonged exposure to excessive temperatures.

Twin Coil Solar

Solar panels can be used to heat the Thermal Store via a high surface area coil, allowing for an efficient heat transfer even during times of the year when the panels aren’t producing particularly high flow temperatures.

The secondary immersion heater can also be used to facilitate Solar PV.

Heat Pump

The addition of a very high surface area coil (usually 3.0m²) allows the efficient input of heat from low-temperature heat sources like Heat Pumps. They’re not ideal as a primary heat source, however, as the optimal store temperature for a Thermal Store is 70°C and heat pumps tend to only produce 55°C.

If a heat pump is used as a heat source, it should be supplemented by another heat source which can reliably boost the store up to 70°C. If there may be occasions where the store temperature can only be raised to 55°C, then we can compensate for this by installing a 50% longer DHW coil, so that the cold mains water has 50% more opportunity to pick up heat. This gives a similar performance to a 70°C store with a standard-length DHW coil.


A space-saving solution when a header tank can not be placed in the loft is to combine it with the cylinder body. This is connected via an integral pipe allowing for tank fill and expansion to be facilitated.

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