Heat-storage quotes mix electrical, plumbing and tariff language. These definitions are written for comparing a domestic proposal rather than studying the underlying engineering.
Core storage terms
Capacity (kWh): the amount of energy a store can hold under stated conditions.
Power (kW): the rate at which energy is charged or delivered.
Phase-change material (PCM): a material that absorbs and releases heat while changing state, commonly between solid and liquid.
Sensible heat: energy stored by raising a material's temperature without changing its phase.
Latent heat: energy absorbed or released during a phase change.
Standing loss: heat escaping while energy waits in the store.
Hot-water and heating terms
Flow rate (litres/minute): how much water passes a point each minute. It is meaningful with the temperature rise.
Flow temperature: the temperature of water leaving a heat source for the heating circuit.
Heat exchanger: a component that moves heat between fluids without mixing them.
Thermal store: a broad term for equipment that holds heat; often used specifically for a vessel that contains primary heating water.
Cylinder equivalent: a maker's comparison with a hot-water cylinder. Check starting and delivery temperatures before comparing claims.
Tariff and control terms
Time-of-use tariff: electricity priced differently at different times.
Charge window: the period when controls allow the store to charge.
Boost: a manual or automatic top-up, which may use a more expensive tariff period.
State of charge: an estimate of how much usable energy remains.
Your next step
Mark any undefined unit or abbreviation in a quote. Ask for a plain-English explanation and the test condition before treating the figure as comparable.
Sources
Primary and independent references checked by our editorial team.
- Energy storage options explained — Energy Saving Trust Checked 10 Nov 2026
- Economy 7 tariff guidance — Ofgem Checked 10 Nov 2026