Every air source heat pump needs electrical work. This guide covers supply requirements, circuit sizing, outdoor unit cable routing, controller wiring, backup immersion circuits, MCS certification, BUS grant implications, and typical costs of £500 to £1,500.
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Written and reviewed by Andrew Moore, founder of Elec-Mate, against BS 7671:2018+A4:2026, IET Guidance Note 3 and the IET On-Site Guide.
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Air source heat pumps (ASHPs) are the leading low-carbon heating technology in the UK. With the government phasing out new gas boiler installations and providing grants of up to £7,500 through the Boiler Upgrade Scheme, ASHP installations are growing rapidly — and every one of them needs electrical work.
The electrical scope of an ASHP installation typically includes a dedicated circuit from the consumer unit to the outdoor unit, cable routing through the property, a local isolator adjacent to the outdoor unit, controller wiring, and often a backup immersion heater circuit. This is distinct from the heating and plumbing work (which is carried out by the MCS-certified heating installer) and represents a significant revenue stream for electricians.
This guide covers the electrical supply requirements, circuit design, cable routing, controller wiring, regulations, MCS considerations, and typical costs.
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The first consideration is whether the existing electrical supply can accommodate the heat pump. Most domestic ASHPs draw 3 to 6kW at full load, which equates to 13 to 26A on a single-phase 230V supply.
Suitable for ASHPs up to approximately 8kW. The existing single-phase supply must have sufficient spare capacity — check the main fuse rating (typically 60A, 80A, or 100A) and the peak demand of the existing installation. A 5kW ASHP on a 100A supply with moderate existing demand is straightforward. On a 60A supply with an electric shower and EV charger already installed, a supply upgrade may be needed.
Required for larger ASHPs (above 8 to 10kW) and for properties where the single-phase supply cannot accommodate the additional load. Three-phase ASHPs distribute the load across three phases, reducing the current per phase. A three-phase supply upgrade involves a DNO application and can take 8 to 16 weeks. Factor this into the project timeline and quote the supply upgrade separately.
Always carry out a maximum demand assessment during the site survey to confirm the existing supply is adequate. If the supply needs upgrading, inform the customer early — it adds cost and time to the project.
The heat pump outdoor unit requires a dedicated radial circuit from the consumer unit. The circuit design must account for:
Use the cable sizing calculator to determine the correct cable size for the specific installation, accounting for all relevant correction factors and voltage drop.
The cable route from the consumer unit to the outdoor heat pump unit is often the most labour-intensive part of the electrical installation. Planning the route during the site survey avoids surprises on installation day.
Most ASHP systems include a controller that manages heating zones, hot water production, and weather compensation. The controller wiring is typically low-voltage signal cabling, but the electrician must connect it correctly.
Most ASHP systems heat domestic hot water via a hot water cylinder. A backup immersion heater is installed in the cylinder to provide hot water if the heat pump is off (for servicing) or during periods of extreme cold when the heat pump alone cannot maintain the required water temperature.
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The Boiler Upgrade Scheme (BUS) provides a government grant of up to £7,500 towards the cost of an air source heat pump installation. This grant has made ASHPs financially competitive with gas boilers and is driving the growth in installations.
If you are considering becoming an MCS-certified ASHP installer (rather than just the electrical subcontractor), you need training in heat pump system design and installation, plus MCS registration via a certification body such as NICEIC, NAPIT, or Elmhurst.
The electrical installation for an air source heat pump must comply with BS 7671:2018+A4:2026 and the manufacturer installation manual. Key regulations from the RAG intelligence include:
The installation is notifiable under Part P of the Building Regulations (new circuit from the consumer unit). Notify through your competent person scheme (NICEIC, NAPIT, etc.) or via Building Control.
The electrical installation cost varies depending on the complexity of the cable route, the distance from the consumer unit to the outdoor unit, and whether the consumer unit needs modification.
These costs are for the electrical work only — the heat pump unit, cylinder, pipework, and plumbing are separate. When quoting, itemise the electrical scope clearly so the MCS installer and homeowner can see exactly what is included.
Elec-Mate's quoting app lets you itemise dedicated circuits, SWA cable runs, isolators, immersion circuits, and controller wiring.
Try it free for 7 daysAir source heat pump installations are one of the fastest-growing segments of domestic electrical work. Every ASHP needs electrical work, and the typical value of £500 to £1,500 per installation makes it a reliable revenue stream — particularly when you build relationships with MCS-certified heating installers who subcontract the electrical work.
Size the dedicated ASHP circuit with the cable sizing calculator. Account for compressor starting current, cable run length, and installation method. Get it right on the survey.
Price ASHP electrical work with Elec-Mate's quoting app. Dedicated circuit, SWA, isolator, immersion, controller wiring — all itemised.
Complete the Electrical Installation Certificate for the ASHP circuits on site. AI board scanning, voice test entry, and instant PDF export for the MCS documentation package.
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