Can a battery run your heat pump?
Usually yes on power, rarely all day on energy. Example: a home needing 60 kWh of heat on a ~0°C day, with a heat pump at COP 2.6, uses about 23.1 kWh of electricity for heating plus 8 kWh for everything else. A single 13.5 kWh battery covers about 41% of that day. Try your own numbers below.
About 9.9 hours at the day's average rate, from 12.83 kWh available.
Heat pump uses 23.1 kWh of electricity; whole home 31.1 kWh.
The battery can power the heat pump at full output (11.04 kW limit).
- Heat pump electricity = 60 kWh of heat ÷ COP 2.6.
- Spreads the day's use evenly over 24 hours; real use peaks in mornings and evenings.
- 5% extra allowed for losses; 0% reserve held back.
- No solar input assumed (a worst-case winter day).
How the calculation works
Heat pump electricity = the heat your home needs that day ÷ the heat pump's COP at that temperature. We add the rest of the house, then compare it with the battery's usable energy (less 5% for losses). We also check that the battery can supply the heat pump's maximum draw plus the average of everything else at the same time. The day-type COP values are typical estimates; use your heat pump's datasheet figure if you have it.
Questions people ask
Can you run a heat pump off a home battery?
Yes. Most home batteries can power a typical domestic air-source heat pump, as long as the battery's continuous power is higher than the heat pump's maximum electrical input plus whatever else is running. The bigger question is how long. For example, a home needing 60 kWh of heat on a day when the heat pump's COP is 2.6 uses about 23 kWh of electricity for heating alone, more than a single 13.5 kWh battery holds.
What size battery do I need for a heat pump?
Work out the heat pump's electricity use on a cold day (heat demand ÷ COP) and add the rest of the house. Covering a whole cold day without solar or cheap-rate recharging often needs far more storage than one battery. Many homes instead size the battery to shift the heat pump onto cheaper overnight electricity. Use the calculator above with your own heat demand.
What is COP and why does it drop in winter?
COP (coefficient of performance) is how many units of heat a heat pump makes per unit of electricity. It falls as the outside air gets colder, so the same house needs more electricity on a frosty day than a mild one.
Will a battery keep my heating on in a power cut?
Only if it's installed for backup (usually with a gateway or backup switch) and the heat pump's circuit is on the backed-up side. Check this with your installer; many systems back up only selected circuits.
Batteries in this calculator
Tesla Powerwall 3
An all-in-one home battery with a built-in solar inverter. One unit stores 13.5 kWh and can be expanded with up to three Expansion units.
Sigenergy SigenStor
A stackable system: a Sigen Energy Controller (hybrid inverter) with 1–6 battery modules of 5.2 or 7.8 kWh usable each.
Fox ESS EVO 10
An all-in-one battery and hybrid inverter with 10.24 kWh of LFP storage, sold in 5, 8 and 10 kW versions. Up to three units can run in parallel.
Enphase IQ Battery 5P
An AC-coupled 5 kWh battery with six built-in microinverters, so it can be added to most existing solar systems. Up to seven can be combined in the UK.
myenergi libbi
A UK-designed modular battery with a 3.68 kW or 5 kW hybrid inverter and 1–4 battery modules (4.6 kWh usable each). Built to work with myenergi's zappi and eddi.
Also see the battery runtime calculator for power cuts.