Heat Pump on Single Phase vs Three Phase
Good news: 95% of UK heat pump installations work fine on standard single phase electricity. Unless you have a very large home needing a heat pump above 16 kW, or plan to run a heat pump and EV charger simultaneously at maximum capacity, your existing electrical supply is almost certainly adequate.
This guide clarifies the differences between single and three phase supplies, when each is needed, and what to do if your supply needs upgrading.
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Single Phase vs Three Phase
| Feature | Single Phase | Three Phase |
|---|---|---|
| Voltage | 230V | 400V |
| Typical fuse | 60A or 100A | 100A per phase |
| Max capacity | 14-23 kW | 69 kW |
| UK homes | ~95% of residential | ~5% (mainly large/rural) |
| Heat pump suitability | Up to ~16 kW | Any size |
Which Do You Need?
Single Phase (Most Homes)
Up to 16 kW heat pump. Covers 2-4 bed homes. Standard 100A supply handles heat pump + normal household load easily.
Three Phase (Large Homes)
16 kW+ heat pumps. Large 5+ bed homes, multiple ground source systems, or commercial properties.
Your MCS installer will assess your electrical supply during the site survey. They will check your main fuse rating, available capacity, and recommend any upgrades needed.
Checking Your Supply Capacity
- Check your consumer unit: One main switch = single phase. Three main switches = three phase
- Check your main fuse: A 60A fuse provides ~14 kW capacity. A 100A fuse provides ~23 kW capacity
- Consider total load: A heat pump (2-5 kW) plus household appliances (3-8 kW) plus potentially an EV charger (7 kW)
Most homes on a 100A supply have plenty of headroom for a heat pump. If your main fuse is only 60A, your DNO (Distribution Network Operator) can often upgrade it to 100A free of charge.
Upgrading Your Supply
| Upgrade | Cost | Timeframe |
|---|---|---|
| 60A to 100A fuse upgrade | Often free from DNO | 2-6 weeks |
| Single phase to three phase | £1,000-5,000 | 6-12 weeks |
Three phase upgrades are rarely needed for residential heat pump installations.
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Calculate what size heat pump your home needs
Try the Free CalculatorSize determines electrical requirements — most homes need single phase only
Frequently Asked Questions
Can I run a heat pump on single phase electricity?
Yes. Most UK air source heat pumps up to 16 kW run on standard single phase 230V. This covers the vast majority of UK homes.
How do I know if I have single or three phase?
Check your consumer unit (fuse box). Single phase has one main switch. Three phase has three. Your installer will verify during the site survey.
Can I upgrade from single to three phase for a heat pump?
Yes, but it costs £1,000-5,000 and is rarely necessary for residential installations. Most installers can specify a single-phase unit that meets your needs.
Will a heat pump trip my electricity supply?
Unlikely with correct installation. A heat pump typically draws 2-5 kW, well within a standard 100A supply. Your installer checks capacity during the survey.
Can I have a heat pump and EV charger on single phase?
Yes, with load management. A heat pump (2-5 kW) and EV charger (7 kW) together are within 100A capacity. Smart scheduling ensures they do not draw maximum power simultaneously.
Electrical Supply and the UK Heat Pump Transition
Concerns about electrical supply capacity are one of the most common questions from homeowners considering heat pumps. The reality is reassuring — most UK homes have adequate single phase supplies for the heat pumps they need. As the Boiler Upgrade Scheme drives adoption, DNOs are also investing in grid capacity. Combined with the right electricity tariff, proper insulation, and potentially solar panels, the electrical infrastructure for heat pumps is already in place for the vast majority of UK properties.