Heat Pump Electrical Requirements
Electrical supply requirements for air and ground source heat pumps — cable sizing, protection, and controls
Heat Pump Types
UK electricians primarily encounter air source heat pumps (ASHPs) in domestic installations, with ground source and hybrid systems in larger properties.
Heat pump types and electrical characteristics
Manufacturer data| Type | Thermal Output | Typical Current Draw | Supply |
|---|---|---|---|
| ASHP (small domestic) | 5-8 kW | 10-16A | Single phase |
| ASHP (large domestic) | 8-16 kW | 16-35A | Single phase |
| ASHP (commercial) | 16-60 kW | 25-90A | Three phase |
| GSHP (domestic) | 6-16 kW | 12-30A | Single phase or three phase |
| Hybrid (ASHP + boiler) | 5-8 kW (ASHP element) | 10-16A | Single phase |
Current draw varies by model. Always use the manufacturer's maximum rated current for cable and MCB sizing.
Circuit Design
Heat pumps require a dedicated radial circuit from the consumer unit with appropriate protection.
Ib = P / (V x PF)- Ib
- = Design current in amps
- P
- = Electrical input power in watts (not thermal output)
- V
- = Supply voltage (230V single phase)
- PF
- = Power factor (typically 0.85-0.95 for inverter-driven units)
BS 7671 Appendix 4
Electrical vs Thermal Power
Cable Sizing and Protection
Typical cable and protection for domestic heat pumps
BS 7671, Table 4D5| Electrical Input | Cable (T&E, Method C) | MCB | RCD |
|---|---|---|---|
| Up to 3 kW (13A) | 2.5 mm² | 16A Type C | 30 mA |
| 3-5 kW (13-22A) | 4 mm² | 25A Type C | 30 mA |
| 5-7 kW (22-30A) | 6 mm² | 32A Type C | 30 mA |
| 7-9 kW (30-40A) | 10 mm² | 40A Type C | 30 mA |
Check voltage drop for runs over 20 m. Apply derating for thermal insulation contact.
External Isolator
Controls and Integration
Heat pump systems require control wiring between the outdoor unit, indoor controller, and any cylinder or zone valve actuators. Most systems use a proprietary low-voltage control bus (5V or 12V) between the outdoor and indoor units — follow the manufacturer's wiring diagram precisely.
Integration with smart thermostats (Hive, Nest, Tado) is possible but must be confirmed as compatible with the specific heat pump model. Many heat pumps use a volt-free contact input for external demand signals.
Immersion Heater Backup