Can You Fit a Heat Pump in an Old House?

Half the housing stock around Wigan, Bolton and the Manchester suburbs was built before anyone had heard of a cavity wall. So the question comes up on nearly every survey of an older property: is this house too old for a heat pump?

The short answer is that age is a poor predictor. We have fitted heat pumps into 1890s terraces that run beautifully and quoted on 1990s detached homes that needed more work than the owners expected. What matters is heat loss, not the date on the deeds.

What the heat loss survey is actually asking

Before any meaningful quote, a room by room heat loss calculation works out how many kilowatts your house leaks on a cold day. That number, not the age of the building, decides the size of the heat pump and whether the existing radiators can deliver the heat at a low flow temperature.

An old house usually loses more heat than a modern one. That is not automatically a problem. It means one of three things: a larger heat pump, some fabric improvements, or a couple of bigger radiators in the worst rooms. Often it is a combination, and often it is cheaper than people fear.

Solid walls are not a dealbreaker

Solid brick walls lose roughly twice the heat of an insulated cavity, and there is no cavity to fill. That sounds fatal until you look at where the heat actually goes in a typical terrace.

In many older homes the biggest losses are the loft, the draughts and the windows, not the walls. Topping up loft insulation to a proper depth, draught proofing the floorboards and sorting the gaps around old sash windows are modest jobs that shift the heat loss figure meaningfully. Internal or external wall insulation is the bigger, more disruptive step, and it is worth doing at some point, but it is rarely the thing standing between you and a working heat pump.

Mid terraces have a quiet advantage here too: two of your four walls are heated by next door. They are frequently the easiest older properties to heat well.

The radiators and the pipework

Heat pumps run best at flow temperatures of around 35 to 45 degrees rather than the 70 a gas boiler uses, so each radiator gives out less heat than it did. Typically most radiators in an older home are already fine, because they were oversized when they went in, and a handful need upgrading. The usual candidates are the big bay windowed front room and any uninsulated extension.

Two things we do look at carefully in older houses. First, microbore pipework, common in homes replumbed in the 1970s and 80s, which can restrict flow enough to need some pipe upgrades. Second, the state of the existing system: decades of sludge in old steel radiators will hamper any heating system, and a proper flush and inhibitor is part of doing the job properly.

What it means for running costs and the grant

A heat pump in a leaky house still costs more to run than the same heat pump in a well insulated one. Seasonal efficiency (SCOP) typically lands between 2.5 and 4, and the weaker end of that range is where poorly insulated homes with high flow temperatures sit. Getting the heat loss down and the flow temperature low is what moves you up the range.

The Boiler Upgrade Scheme grant is not affected by the age of the property: £7,500 towards an air source heat pump, or £9,000 if you are off the gas grid on oil or LPG. We claim it on your behalf and it comes off the price. Heat pumps start from around £3,000 after the grant, and the install is usually a 2 to 3 day job.

The honest test

If someone quotes for an older property without doing a full heat loss survey, treat the number with suspicion. The survey is what tells you whether your house is a straightforward swap, a swap plus two radiators, or a project worth staging over a couple of years.

Our survey is free and there is no obligation. We will measure the house properly, tell you what it would genuinely take, and say so plainly if the honest answer is not yet.