A hot-water heat battery replaces or supplements storage for taps and showers. A whole-home heat battery must also meet space-heating demand. The second job is much larger and needs a building-level design.
The short answer
Do not compare these products by box size or brand alone. A hot-water-only store is sized around bathing and tap use. A whole-home system is sized from heat loss, outdoor conditions, emitter demand and the hours between charges.
| Question | Hot-water store | Whole-home store |
|---|---|---|
| Main demand | Showers, baths and taps | Rooms plus domestic hot water |
| Design input | Water-use pattern and flow | Room-by-room heat loss and hot water |
| Electrical load | Often smaller | Can be substantial |
| Existing system | May leave boiler or heat pump in place | May replace the main heater |
Why this changes the quote
Whole-home storage may require changes to radiators, pipework, controls and the incoming electrical supply. It also needs a plan for the coldest design day, not only an average winter day.
Government support uses a strict boundary
Announced Boiler Upgrade Scheme support for heat batteries is tied to systems capable of providing space heating and hot water under the planned criteria. A compact hot-water replacement should not be assumed eligible.
Hybrid arrangements
A store may work alongside another heat source. Ask which appliance leads, when the other starts, and whether peak-rate electricity or fossil fuel fills any gap.
Your next step
Circle every load the proposed unit will serve on a simple house plan. If rooms and taps are both circled, require a full heat-loss calculation and electrical load assessment.
Sources
Primary and independent references checked by our editorial team.
- Energy storage options explained — Energy Saving Trust Checked 10 Nov 2026
- Boiler Upgrade Scheme and certification requirements — GOV.UK Checked 10 Nov 2026