Heat pumps explained

With air source heat pumps (ASHPs) becoming a familiar sight on UK properties, more electricians are being called upon to support installations. Rob Dyer, Technical Sales Support Engineer for Grant UK, explains the essentials every electrician should understand when working with heat pumps.

What are ASHPs and what part do electricians play in installing heat pumps?
ASHPs draw energy from the outside air and convert it into usable heat for a wet heating system by using the vapour compression cycle. This cycle involves key components including the compressor (the hardest working part of the unit) and the evaporator fan, which moves air across the heat exchanger.

While heating engineers manage the plumbing, cylinder replacement and commissioning of the system, an electrician’s role is to ensure the heat pump and controls are safely connected to the electricity supply, compliant and correctly wired. Their time on-site may only be half a day to a full day, but their role is essential to ensuring the heat pump operates efficiently and reliably.

What are the main responsibilities for electricians?
Electricians have two key roles in a heat pump installation. The first is connecting the heat pump to the power supply using an appropriate size of cable which will typically be a 16A to 32A supply. A heat pump requires a dedicated power supply with a correctly sized circuit breaker. The final connection must run through a weatherproof, lockable isolator positioned outside the property, with the cable either armoured or run in flexible conduit between the isolator and the heat pump.

The second step is connecting the heat pump with the controls and wiring centre fitted inside the property. The heat pump controller acts as the system’s brain, managing pumps, valves, thermostats and temperature settings, with its display showing operational data so the installer and homeowner can see what’s going on. Most heat pump systems are similar to a W-plan, and if you understand a Y- or S-plan heating system, you will understand a W-plan, which is in essence a hot water priority system with a 3-port diverter valve.

How important is the controller setup?
The controller is crucial because correct configuration is essential for reliable operation. Most system issues stem from incorrect setup rather than faults elsewhere. Grant’s Aerona Smart Controller simplifies the initial setup through its built-in configuration assistant that asks clear questions to guide the installer or electrician, allowing them to check each system component is set up and working properly.

What should electricians keep in mind during installation?
One of the most common misunderstandings is that a 10kW heat pump requires a 50A supply. In reality, the 10kW rating refers to the heating output not the electrical demand. Confusing the two could lead to unnecessary oversizing, for instance, using a 10mm cable when a 2.5mm might be ok.

It is also important to use the correct RCD protection. Most heat pumps are inverter-driven, meaning Type B or Type F RCDs are suitable but Type A or AC RCDs are not. Electricians should also be aware that R290 refrigerant models have restricted safety zones around the unit where isolators or switches cannot be installed.

Before installation begins, either the installer or electrician must confirm that the property’s electricity supply can support the heat pump. This check is made through the ENA Connect Direct Portal, which links to the local Distribution Network Operator (DNO). If the criteria is met, installation can proceed under a ‘Connect and Notify’ process and the DNO can be informed after commissioning. Grant’s Aerona³ and Aerona 290 heat pumps are fully compliant with this process.

Are any tools or equipment particularly useful for heat pump electrical work?
No specialist tools are needed, but some make the job much easier. Bootlace ferrules, for instance, are helpful for connecting small-core cables to terminals and shielded twisted pair or Cat 5/6 data cable is handy for the wiring. A multimeter is always useful to have on the van as it helps with fault-finding and checking sensor resistance. 

What qualifications do electricians need to work with heat pumps?
Electricians must hold a formal electrical qualification to complete the electrical connections and to sign off work to Building Control. They should be qualified to the latest version of BS 7671 and ideally should be members of a Competent Person Scheme (CPS) such as NICEIC. A strong understanding of heating system wiring is also important and familiarity with hydronics and plumbing helps too. 

What support does Grant UK offer for electricians?
Grant UK has lots of resources that support electricians working with heat pumps. Our Training Academy offers dedicated wiring sessions as part of the Aerona³ and Aerona 290 ASHP Installer Courses, allowing electricians to gain hands-on experience with heat pump systems. 

We also have heat pump specialists available on the phone and in the field to provide technical assistance, offer wiring diagrams for different scenarios, and our eLearning Academy has a free webinar which is specifically for electricians. It explains how ASHPs operate and explores the electrician’s role in completing installations. Electricians can access the Grant eLearning Academy at grantelearning.com, registering for an account using the enrolment key GUKWEB0820 and then enrolling onto the Heat Pump Q&A Webinar. 

Why should electricians consider expanding into heat pumps?
The move towards low-carbon heating is opening up real opportunities for electricians. Although electrical and plumbing trades are distinct, both can expand their skills with the right training and qualifications. Many electricians are already taking this route, adding renewable heating to their skillset as demand for heat pump installations grows.

As the UK continues its shift towards cleaner energy, there is every reason to get involved in this expanding sector.

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This article appeared in Electrotechnical News November/December 2025 edition – read it here