Heating a House Extension with a Heat Pump

Kitchen extensions, garden-room extensions and open-plan living spaces are some of the most common jobs we fit. They usually share a few features: a large floor area, a lot of glass (bifolds, roof lanterns, sliding doors), and a heating plan that was left until late in the build.

The problem with “just add a radiator”

Extending your central heating into a new extension sounds simple, but it can raise several questions:

• Boiler capacity. Your boiler was sized for the original house. A big open-plan extension with lots of glazing may need more heat than it has spare.
• Wall space. Bifolds and kitchen units leave little wall for radiators, which is why so many extensions end up with underfloor heating instead.
• Summer overheating. Large glazed extensions, especially south or west-facing ones, get very warm in summer. Radiators and underfloor heating can't help with that.

How a heat pump fits an extension

A Haier heat pump heats the extension independently of the boiler. The indoor unit only needs a short stretch of wall high up, and the outdoor unit sits outside nearby. It warms the space in minutes, and on hot days it switches to cooling. For large open-plan spaces we often fit a 5.0kW unit, or two smaller units at either end of a long room.

Fitting during the build

The best time to plan air conditioning is while the extension is being built. The pipe routes can be run inside the walls or ceiling void before plastering, and a dedicated electrical supply can go in with the rest of the first-fix electrics. That gives a cleaner finish, with less visible trunking and pipework. We're happy to work alongside your builder and electrician.

Already finished? That's fine too. Most retrofit installs in extensions take a day, with the pipe run kept short by putting the outdoor unit close to the new wall.

Underfloor heating and a heat pump together

If your extension already has underfloor heating, a heat pump still earns its place. Underfloor heating is slow to respond and can't cool. Many customers use the heat pump for fast heat on cold mornings and for cooling in summer, and let the underfloor run in the background.

Running costs

A 5.0kW Haier unit costs about 36.6p an hour at full heating output at the October–December 2026 electricity cap of 26.32p per kWh, and less once the room is up to temperature. See heating costs compared for how that compares with other options.

Haier systems, certified installers

We install Haier exclusively. Keeping to one brand means our engineers know the range inside out, we hold the right spares, and costs stay down. Haier systems come with a 6-year warranty as standard when installed by a certified engineer. Our engineers are F-Gas certified, the business is REFCOM registered, and electrical work is carried out to Part P standard. We're based in Buckingham, MK18, and cover Milton Keynes, Buckinghamshire, Northamptonshire and the surrounding area.

Heat pump installers near you

Milton Keynes Buckingham Bletchley Newport Pagnell Aylesbury Bicester Northampton Oxford

See the full list of areas we cover, or check recent installations for real examples of our work.

More heating guides

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Common questions

How do I heat a new extension?

Options include extending the central heating, underfloor heating, or an air to air heat pump. A heat pump heats the extension independently of the boiler, needs only a small area of wall, and also cools the space in summer.

Will my boiler cope with an extension?

Not always. Boilers are sized for the original house, and a large, heavily glazed extension can need more heat than a boiler has spare. A heat pump avoids that question for the new space.

What size unit does a kitchen extension need?

Large open-plan kitchen extensions often need a 5.0kW unit, or two smaller units in long rooms. Glazing area and orientation matter as much as floor area. We confirm it at survey.

Can you install while the extension is being built?

Yes, and it gives the neatest result. Pipework and power can be run before plastering, and we are happy to coordinate with your builder and electrician.

Can I have underfloor heating and a heat pump?

Yes. Many customers use the heat pump for fast heating and summer cooling while the underfloor heating runs in the background.