Heat Pump Electrical Requirements
Heat pumps are a growing electrical job. The work is about supply capacity, a dedicated circuit and correct isolation — not the refrigeration side.
Air-source heat pumps are being fitted in large numbers as homes move away from gas. For the electrician, the job is providing a suitable supply — a dedicated circuit sized for the unit, with proper isolation — and checking the existing installation can take the extra load.
This guide covers what a heat pump needs electrically: assessing supply capacity, sizing the circuit, providing isolation, and coordinating with the heating installer.
Key takeaways
- Most domestic air-source heat pumps run on a single-phase dedicated circuit.
- Assess existing maximum demand — a heat pump adds continuous load that may stress the main fuse.
- Provide a local isolator at the outdoor unit for maintenance.
- Size the cable for the running load, start current and volt drop over the outdoor run.
- Coordinate with the heating engineer on controls and any immersion/backup heater wiring.
Assessing the supply
A heat pump draws a steady load whenever it runs, often through the coldest part of the year. Add that to the existing maximum demand and check it against the main fuse — a home with a shower, cooker and EV charger may not have the headroom without load management or a supply upgrade.
This assessment is the first thing to do, because it can change the whole scope of the job.
Check the headroom first
Run the existing maximum demand with diversity, then add the heat pump — TradePlanr's max demand calculator makes that quick.
The dedicated circuit
Run a dedicated circuit from the consumer unit to the heat pump, sized for the running current and starting characteristics, with protection to suit. Check volt drop over what is often a long run to an outdoor unit at the side or rear of the property.
Follow the manufacturer's data for the maximum overcurrent protective device and cable requirements — these vary by model.
Isolation and outdoor considerations
Provide a local means of isolation at the outdoor unit so it can be worked on safely without returning to the consumer unit. Use suitably rated, weatherproof equipment for the outdoor environment.
Any backup or immersion heater in the system may need its own supply — confirm the arrangement with the heating installer.
Coordinating and certifying
Heat pump installs are a joint job with the heating engineer, who handles the refrigeration and controls while you provide and certify the electrical supply. Agree the interface — controls wiring, sensors and any backup heater — up front.
Certify the new circuit with an EIC, as with any new circuit, and record the test results.
Certify the new circuit
TradePlanr's EIC captures the heat pump circuit and its test schedule ready to sign on completion.
Frequently asked questions
Does a heat pump need a three-phase supply?
Most domestic air-source heat pumps run on single phase. Larger units or commercial systems may need three phase — always check the manufacturer's data for the specific model.
Will my consumer unit take a heat pump?
It depends on spare ways and, more importantly, on whether the supply has capacity. Assess existing maximum demand plus the heat pump against the main fuse before assuming a spare way is enough.
Is a heat pump circuit notifiable?
Installing a new circuit for the heat pump is notifiable under Part P and is certified with an EIC.
From guidance to action
Related guides
How to Calculate Maximum Demand (with Diversity)
Applying diversity to work out realistic maximum demand for a domestic installation.
Consumer Unit Upgrades Explained
What a consumer unit change involves — assessing the existing installation, RCBO boards and paperwork.
Cable Sizing to BS 7671
The full cable sizing method — design current, correction factors, tabulated ratings and volt drop.
