Designing Around a Heat Pump: The Room Changes Nobody Warns You About
Guest Author: James Stalker, MCS-accredited heat pump installer, Exmouth, Devon
Most of the houses I work in are Devon originals: thick stone or cob walls, an oil tank round the back, and no one who built them ever imagined central heating, let alone a heat pump. Homeowners brace themselves for the heat pump.
What catches them out is everything the rooms around it have to do to accommodate one.
A boiler swap barely touches a house. A heat pump does.
Designing Around a Heat Pump
The cylinder has to live somewhere, some radiators have to grow, and the outdoor unit ends up on a wall someone can see. Settle those early, and they disappear into the design. Leave them for the installer to sort on the day, and you’ll be arguing about a radiator position for weeks.
The Cupboard You Lose, and the One You Gain
Most combi boilers live in a kitchen cupboard or an airing cupboard, tucked away and forgotten. A heat pump needs a hot water cylinder instead, and that cylinder needs somewhere to live.
It’s not a huge unit, but it’s not nothing either, and where it ends up changes what a room can be used for.
On a large family home near Ottery St Mary, three installers before us told the owners their cylinder couldn’t be moved out of the space they wanted back. We redesigned the pipework and put it in the garage instead, and they got their cupboard back for storage.
On a period property in Newton Abbot, relocating the cylinder was what let the owners finally go ahead with a bathroom extension they’d been planning. In both cases, the room the cylinder used to occupy became more useful once it moved, not less.
The lesson for anyone planning around a heat pump: decide the cylinder’s new home at the same time as the radiators, not after the pipework is already in the wall.
Radiators That Suit a Lower Flow Temperature
An oil or gas boiler typically pushes water round a house at 70 to 80°C. A heat pump runs at 45 to 50°C, which is gentler on an old property and cheaper to run, but it means some radiators need to be larger to deliver the same heat.
On a six-bedroom 1930s house in Exmouth, we upgraded seven radiators to hit a 47°C design flow temperature and left the rest alone. On a smaller retrofit in Newton Abbot, one radiator did the job and the rest stayed exactly as they were, because a proper heat-loss survey told us they didn’t need touching. It depends entirely on the room, not the house.
This is where the interiors decisions start. A radiator that has to grow can grow taller and slimmer rather than wider, which suits a narrow wall far better than a bulky, low one.
Bathrooms are a good spot to swap a standard panel radiator for a high-output designer towel rail; it does the job and looks chosen rather than fitted. A room-by-room heat-loss calculation from an installer such as Eco Pro Renewables is what tells you which radiators actually need to change, rather than swapping the lot on a guess.
Living With the Outdoor Unit
The outdoor unit is the part people worry about most before they’ve actually seen one working. They’re quiet, and every installation gets a sound calculation as part of its MCS sign-off.
The mistake is boxing it in too tightly for the sake of tidiness. It needs air moving through the coil to work properly, so any screening has to let air through rather than sealing it off.
Trellis, slatted fencing or planting set with a gap behind it works far better than a solid enclosure.
The Grant, While it Lasts
None of this changes the fact that most of my customers are doing this because the Boiler Upgrade Scheme currently takes £7,500 off an air source heat pump, rising to £9,000 for homes coming off oil or LPG (details on gov.uk).
It runs to March 2027, which is worth checking before the room planning starts, because it changes what’s affordable.
Most of the arguments I watch homeowners have with their installer are about a decision that should have been made at the design stage, weeks earlier, over a cup of tea. Make them then, and there’s nothing left to argue about on the day.
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