I've finally made the switch from gas to an air source heat pump and thought I'd share a summary of the installation. My house is a 1958 four-bed detached in the West Midlands that we fully renovated in 2021. At the time I was told the classic "too old for a heat pump" line, so I settled for a gas boiler, but I made sure the radiators were oversized and the long pipe runs were 22mm. When we extended the kitchen in 2023, I specified tightly spaced underfloor heating. Those early decisions meant that when the 2025 permitted development changes finally let me site a unit on the boundary, the house needed very little work: about 7m of pipe upsized from 22mm to 28mm, the UFH circulation pump removed, and a more powerful towel radiator in the bathroom.

Based on my own heat loss calculations, I went for a Kronoterm Adapt 0312 in the Corten steel finish. It blends into the garden far better than a white box, and all the pipework and wiring is hidden in the base. Solaris Energy (the UK Kronoterm distributor) handled the design, MCS paperwork and commissioning. A local plumber did the plumbing as their MCS subcontractor, which cut the quote considerably by avoiding travel and overnight costs from Kent. I did the groundworks myself: an 18m trench (🥵) for the buried insulated pipes and cables (breaking two drainage pipes along the way 🤬), plus a 300mm concrete base with a soakaway. I also wired in the KSM2 controller after my electrician let me down. My existing Mixergy cylinder turned out to be "heat pump ready" only after adding its HP integration kit, which cost about £500.

The system was commissioned in September 2026. The water was treated to VDI 2035 standards with a deioniser rather than dosed with inhibitor. The old 35kW boiler is gone and the gas meter has been removed.

There's one minor niggle, a gurgle from the evaporator during hot water cycles, which Kronoterm are looking into.

On installation costs, Solaris' original quote was £16,200. Using the local plumber brought it down to £13,800. The electrician and materials added around £1,360, for a total of about £15,100. After the £7,500 Boiler Upgrade Scheme grant, I paid a little over £7,500.

Hot water has been the first real test, and the early numbers are encouraging. Before the heat pump, I heated my Mixergy with the immersion on the Octopus Intelligent Go off-peak rate, which worked out cheaper than my 80%-efficient gas boiler. On the same day a year apart, the heat pump fully charged the 210L tank in about an hour. It delivered roughly 8kWh of heat for just 2.5kWh of electricity. At off-peak rates, the full tank cost me about 17p, compared with around 49p on the immersion and 62p with gas. That's a 66% saving against the immersion and 73% against the boiler. Off-peak prices of course, but a solid start!

I've been monitoring my gas boiler with Open Energy Monitor and a Kamstrup heat meter for years, so after this winter, I'll be able to do a proper like-for-like comparison. I'm planning a full performance write-up in spring 2027.

The full story, with photos and a detailed cost breakdown, is on my blog: My Heat Pump – @tomasmcguinness