Is my house suitable for a heat pump? A straight answer

Nine times out of ten, somebody asking me "is my house suitable for a heat pump" is asking about the wrong thing. They ask about the age of the house. Age barely matters. What matters is how fast the building loses heat, whether the radiators can give that heat back at a lower water temperature, and where the hot water cylinder is going to live.

I have fitted heat pumps in 1890s stone terraces that work beautifully and turned down 2004 estate houses because there was nowhere sensible for a cylinder. Here is what I actually look at on a survey, and what we fit, which is on the air source heat pumps page.

Is my house suitable for a heat pump? What actually decides it

A heat loss survey, room by room, measuring the walls, the glazing, the insulation and every existing radiator. That is the whole answer, and anyone telling you yes or no without doing one is guessing.

What the survey produces is a number in kilowatts for the coldest day of the year at your postcode, and a flow temperature the system has to hit to deliver it. Lower flow temperature means better efficiency. A well-designed system runs at around 45°C and returns three to four units of heat for every unit of electricity. Push the flow temperature up to boiler levels and that ratio falls away.

Everything else people worry about is really a question about one of those two numbers.

Do I need new radiators for a heat pump?

Usually some, rarely all.

A heat pump runs cooler water than a gas boiler, so each radiator gives out less heat than it used to. The fix is more surface area: a taller radiator, a double instead of a single, or occasionally a fan-assisted one where there is genuinely no wall space.

On a typical semi it comes out at two or three radiators, and it is usually the same ones: the lounge, because it is the biggest room, and a bedroom where somebody put a small radiator under a window years ago. Underfloor heating downstairs is ideal and needs nothing doing at all.

The survey tells you which ones. If an installer says every radiator in the house has to go, ask to see the room-by-room figures, because that is either a badly insulated house or a lazy design.

Where does the hot water cylinder go?

This is the question that decides more jobs than insulation ever does.

A heat pump heats your water in a cylinder, the way a system boiler does. If you are on a combi, you have probably had no cylinder for fifteen years and the airing cupboard is now a wardrobe. Finding a home for one, with space around it for the pipework and the controls, is the real constraint in a lot of modern houses.

Usual spots: the old airing cupboard, a loft with a decent floor and access, a garage, or under the stairs. It has to be somewhere the pipe runs are short and somewhere you can get at it for servicing.

If there is genuinely nowhere, that is one of the few honest reasons to say no to a heat pump, and I would rather say it at the survey than halfway through the install.

Is my house too old for a heat pump?

No, not on its own. An old house is a heat loss problem, not a heat pump problem.

Solid wall, single-skin stone cottages around Bradfield and the Peak edge lose heat quickly, so the design needs a bigger unit and more radiator surface, and the running cost is higher than it would be in a modern box. That is true of the gas boiler in there now as well. The heat pump just makes it visible.

What changes the answer for an old house is loft insulation and draughts. Doing the loft first is cheap and it makes everything after it smaller and less expensive. What does not change the answer is the EPC letter on its own: EPCs are a blunt instrument and they penalise electric heating, so I have seen good candidates score badly and the other way round.

The Boiler Upgrade Scheme no longer requires you to clear insulation recommendations before applying, which used to catch older houses out.

How much space does the outdoor unit need?

Less than people fear, but it needs to be the right space.

The unit wants a solid base, clear air in at the back and out at the front, and room for the pipework and the condensate drain. A metre of clear space in front is the rough rule. It cannot go in a boxed-in alley with a fence a foot away, because it will be breathing the cold air it has just thrown out.

On planning, an air source heat pump is permitted development on most houses in England as long as the installation complies with MCS 020 a). The outdoor unit must be no more than 1.5 cubic metres on a house, or 0.6 on a block of flats. Detached houses get the first two units as permitted development, everything else gets the first one. Listed buildings and scheduled monuments are out, and conservation areas restrict walls and roof slopes facing a highway.

The noise assessment that goes with MCS 020 a) has to show 37 dB(A) or less at the assessment position, which is a metre from the nearest habitable room window or door of a neighbouring property. That is what really decides where the unit goes, and there is more on it in how noisy is a heat pump.

What about the electrics?

The unit needs its own circuit and the supply has to take the load. Most houses are fine. A 1930s semi with a very old consumer unit and a small main fuse may need work, and that is worth knowing before you commit.

We also notify the network operator that owns the wires in your street, the same as we do for solar.

A worked example: a 1960s four-bed semi

Underfloor heating downstairs, six radiators upstairs, cavity walls, loft insulation topped up two years ago. Gas combi at the moment, so no cylinder.

Heat loss survey puts the design load comfortably inside a mid-range monobloc. Underfloor takes the ground floor with no changes at all. Two of the six upstairs radiators come out for taller doubles, the other four stay. The cylinder goes in the corner of the garage, which is the tidiest run in the house, and the outdoor unit goes on the side elevation where the noise assessment passes at the neighbour's bedroom window.

That is a straightforward job, and it is the commonest shape of job we do. The £7,500 grant is claimed by us as an MCS certified installer, the voucher is issued in your name, and it comes off the quote before you pay anything.

When I say no

When there is nowhere for a cylinder and the customer will not lose the space.

When somebody wants to keep every radiator and run the system at boiler flow temperatures, because they will get a bill they hate and blame the technology.

When the house is about to be extended or re-roofed, because the design will change and so will the heat loss.

And when a gas boiler fitted two years ago is working perfectly and money is tight. There is no shame in waiting. A heat pump is a fifteen-year decision, and the grant has been there a while.

Finding out for certain

Heat pump cost after the grant covers the money and the Boiler Upgrade Scheme rules, and how noisy is a heat pump covers siting, the noise assessment and planning.

If you want the room-by-room answer for your own house, Get a quote with your postcode and we will book a heat loss survey. Or ring 01709 278248 and describe the house to us first.