“Thermal store” can mean any equipment that stores heat, but UK heating discussions often use it for a vessel containing primary heating water. “Heat battery” is frequently used for phase-change or solid-core storage. Product documents matter more than the label.
The short answer
Compare what sits inside, which water is stored, how heat enters and leaves, and whether the unit serves taps, heating or both. A thermal store may combine several heat sources; a compact heat battery may prioritise energy density.
Domestic water arrangement
Some thermal stores hold primary water and heat mains water through a coil or plate exchanger. Some heat batteries also heat mains water on demand. Others form part of a closed heating circuit.
Temperature and volume
Water storage is intuitive to measure in litres but useful capacity still depends on temperature. Phase-change and solid stores are better compared in usable kWh with output conditions.
Multiple heat sources
Thermal stores are often chosen to accept input from boilers, solar thermal, stoves or heat pumps. Check coil positions, temperatures and control priority. A heat battery needs explicit approval for each source.
Space and weight
Compact thermal materials may reduce volume, but installed weight and service space remain. Water stores can be large and structurally demanding when full.
Maintenance and repair
Ask which components are replaceable, who services the heat exchanger and how the vessel is drained or isolated.
Your next step
Draw arrows into and out of each proposed store. Label every heat source and load. If the installer cannot complete the diagram, the comparison is not ready.
Sources
Primary and independent references checked by our editorial team.
- Energy storage options explained — Energy Saving Trust Checked 10 Nov 2026