A beginner's guide to heat pumps in old buildings

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29 Jul 2026

A beginner's guide to heat pumps in old buildings

Heat pumps and old buildings: the myth and the reality

If you own a Victorian terrace, a Georgian townhouse or a stone-built cottage, you have probably heard that heat pumps are only for new-builds with underfloor heating and airtight walls. That is not true. Thousands of older UK homes run happily on air source heat pumps, but they need a different approach from a modern new-build. The secret is not to force the building to change overnight. It is to understand how the house loses heat, improve what you can, and size the system around the property you actually have.

This guide walks you through the practical basics: how air source heat pumps work, why insulation and radiators matter, and what to do before you commit.

How an air source heat pump works in a period property

An air source heat pump sits outside and absorbs low-grade heat from the air, even when it is cold. It uses a compressor and refrigerant to raise that heat to a temperature useful for your home, then transfers it to water that feeds your radiators, underfloor heating or hot water cylinder.

Unlike a gas boiler, a heat pump runs best at lower flow temperatures. A boiler might send water to radiators at 70–80°C. A heat pump typically works at 45–55°C, and sometimes lower. That lower temperature means it runs more efficiently, but it also means your existing radiators may not be big enough to heat each room comfortably. The two key numbers are the heat loss of your home and the output of your emitters.

Fabric first: insulation, draughts and breathability

Before anyone sizes a heat pump, reduce the heat your home loses. In an old building, this does not mean sealing every gap with modern plastic. It means working with the building’s original design, which was often breathable.

Loft insulation: top up to 270–300mm if you can. This is usually the cheapest, easiest win.
Draught-proofing: chimneys, floorboards, sash windows and doors. Use brushes, seals and temporary covers, but keep ventilation for open fires and gas appliances.
Solid walls: avoid cement renders and impermeable paints. They trap moisture. If you insulate internally, use breathable materials such as wood fibre or lime plasters, and consider the risk of interstitial condensation.
Windows: secondary glazing or well-fitted shutters can make a big difference without ripping out original sash windows.
Floors: insulate under suspended timber floors if you can access them. Keep air bricks clear.

Good ventilation matters too. Old buildings need to breathe. Extractor fans in kitchens and bathrooms, plus trickle vents, help control damp without wasting heat.

Radiator sizing and emitters: the make-or-break detail

Once your heat loss is lower, you can work out what emitters each room needs. A heat pump at 45°C needs larger radiators than a boiler at 70°C to deliver the same heat. Your installer should carry out a room-by-room heat loss calculation, not just a whole-house guess.

Options include:

Larger radiators: often the simplest swap. A double-panel radiator can replace a single, or a wider one can fit under a window.
Fan-assisted radiators: useful where wall space is tight. They boost output at low flow temperatures.
Underfloor heating: ideal in renovation projects, but disruptive. It works beautifully with heat pumps if you can add insulation below.
Pipework: older microbore pipes may struggle with the higher flow rates a heat pump needs. Some upgrades may be necessary.

Do not skip this stage. Oversized radiators are not a problem; undersized ones will leave you cold and disappointed.

Practical steps before installation

Here is a sensible order of events for a period property:

Get a heat loss survey. Choose an installer who has experience with old buildings, ideally MCS-certified. Ask for room-by-room calculations.
Improve insulation and draught-proofing first. This reduces the size of the heat pump you need and lowers running costs.
Plan the outdoor unit position. It needs good airflow, away from bedrooms if possible, and should not cause noise nuisance. In England and Scotland, permitted development rights usually apply, but listed buildings and conservation areas may need consent.
Check your hot water cylinder. Most heat pumps work best with a larger cylinder, often 200–300 litres for a family. It needs space and good insulation.
Look into grants. Government grants such as the Boiler Upgrade Scheme can help with upfront costs in England and Wales. Check current eligibility before you buy.
Agree a commissioning plan. The installer should set weather compensation, balance radiators, and show you how to run the system efficiently.

Living with a heat pump in an old home

Heat pumps prefer steady, low-level warmth rather than quick blasts. Set your heating to come on earlier and run for longer at a lower temperature. Use weather compensation so the flow temperature adjusts with the outdoor temperature. Keep doors and curtains closed where possible, and do not turn radiators off in unused rooms for long periods — the system works best as a whole.

Running costs depend on your electricity tariff, insulation and how you use the system. A well-installed heat pump in an old building can be cheaper to run than gas, especially with a specialist heat pump tariff. It also cuts carbon emissions as the grid gets greener. With the right preparation, your period property can be warm, efficient and full of character for decades to come.

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5 Comments

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- John Abraham says Jul 21, 2024 at 10:00am
  
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  - Robert Sonnysays Jul 21, 2024 at 10:00am
    
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Robert Sonny says Jul 21, 2024 at 10:00am

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