Thermal stores hold a reservoir of warm water for a building’s hot water or heating system to draw from rather than inlet temperature cold water. These reduce heating demand.

Thermal stores are typically large, well-insulated water tanks which keep water for hot water or central heating systems warmer for longer. A thermal store can however comprise of a dedicated material located around the coils installed for a ground source heat pump or integrated into the foundations of new buildings. This saves money and abates carbon dioxide (CO₂) emissions by increasing the efficiency of a building's heating system.

Thermal stores can also increase the effectiveness of Biomass and Biogas & Biomethane heating, Micro-Combined Heat and Power systems, Heat Pumps, and Solar Water Heating.

Biomass heating systems, particularly log burning ones, are more efficient when burning greater quantities of biomass quickly in one instance, than burning lower quantities at intervals over the course of a day (this is also less labour intensive). With a thermal store, greater quantities of biomass can be burnt at once and the excess heat stored for use later.

Like biomass, biogas heating systems are also most efficient when burning their fuel quickly, so a thermal store can benefit this type of heating system by storing excess heat for later.

Regardless of fuel source, micro-combined heat and power systems are most efficient when run consistently. For this technology, a thermal store could be beneficial, saving heat for periods of the day when it is needed if the heat is not required constantly.

Similarly, heat pumps benefit from not having to cycle on and off as often, reducing wear and tear on the compressor and condenser, decreasing maintenance costs. Less cycling also reduces heat pumps’ electrical requirements, making them more efficient to run and increasing return on investment and emissions abatement.  Heat pumps running in conjunction with a thermal store cycle less because they run for longer to heat up the larger reservoir of water in the thermal store, then stay off for longer as the thermal store's hot water is used.

Solar water heating systems also benefit from having a thermal store as this will decrease auxiliary (more carbon-intensive) boiler use, particularly after sunset and on cloudy days following sunny days where solar water heating output has been high. The proportion of hot water provided by the solar water heating system will increase when combined with a thermal store, again increasing return on investment and carbon abatement.