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Do you need new radiators for a heat pump? In a Devon home, not all of them, and often not many. Some rooms need a bigger panel, a handful need nothing done at all, and a few need something more considered than either. What decides which is which is a room-by-room heat loss survey, not the age of your radiators or a rule someone read on a forum.
Key Takeaways
- In a typical Devon home only some radiators change, usually to a bigger panel, and a full-house replacement is the exception.
- A heat pump runs your radiators at a lower flow temperature, typically 45 to 50°C, against a boiler’s 70°C or higher.
- At that lower temperature a radiator gives out well under half the heat printed on its boiler-rated label.
- A room-by-room heat loss survey is the only way to know which radiators change and which stay, on any property.
- Narrow microbore pipework, found in some older systems, is a genuine but usually fixable consideration, not an automatic block.
- We don’t quote a radiator-change cost until the £250 plus VAT survey tells us which rooms need one, and that fee is waived if you go ahead with the installation.
The worry has a real cause. A heat pump runs water through your radiators at a noticeably lower temperature than a gas or oil boiler does, and a radiator fed cooler water gives out less heat than the number stamped on its side. That is the mechanism behind “you’ll need all new radiators”, and once you know it, the question turns into a calculation worked room by room on your own house.
Do I Need New Radiators for a Heat Pump? The Short Answer
It depends on the room, not the whole house. Some radiators in a typical Devon property are already generous enough to work at a heat pump’s lower running temperature and stay exactly where they are. Others are undersized for the room once the water running through them is cooler, and those get upgraded to a bigger panel. Replacing every radiator in the house is the exception, and a company that quotes it as standard without measuring anything first is taking a shortcut.
Stays. Already generous enough for its room at the lower flow temperature.
Bigger panel. A taller or double-panel radiator in the same spot.
Underfloor. Only where that floor is coming up for another reason.
An example to show the pattern, not a survey result. Your own rooms get measured one by one.
Much of the fear online starts here. James works as a freelance MCS assessor for NAPIT, auditing other installers’ finished jobs alongside running his own. When a heat pump never gets the house properly warm, the cause he usually finds is a system sized off a rule of thumb, radiators included, with no room measured. Get the sizing right and the radiator question mostly answers itself.
Why a Heat Pump Changes What a Radiator Can Do
A gas or oil boiler typically sends water round your system at close to 70°C or higher. A heat pump is designed to run cooler, usually 45 to 50°C, because that is where it works efficiently instead of straining for a boiler-style peak. The lower flow temperature is the whole point of the technology.
The trade-off is that a radiator rated for a boiler’s higher temperature puts out noticeably less heat once the water feeding it is cooler. Independent radiator-sizing figures put the drop at well under half of a panel’s boiler-rated output at heat pump flow temperatures.
One radiator, two flow temperatures (illustration)
Energy Saving Trust’s installer guidance works in that order: size the heat pump to the property’s measured heat loss, choose a flow temperature, then check whether each existing radiator, run at that temperature, still covers its room. That check is why some radiators need to grow and others never move.
Which Radiators Stay, and Which Change for a Heat Pump
Three patterns turn up again and again once a heat loss survey is actually carried out. The first two come down to how close each radiator already was to its room’s limit.
Already generous for its room
- Its history Sized for a boiler run hot to cover a draughty wall or big window
- At 45 to 50°C Still has enough spare output to cover the room
- The work None. It stays where it is on the wall
Already close to its room’s limit
- Its history Only just covered the room, even at boiler temperature
- At 45 to 50°C Falls short once the water running through it is cooler
- The work A taller or double-panel version in the same spot
The third is underfloor heating, in a small number of rooms, most often where a floor is being lifted for another reason anyway. Retrofitting it purely to dodge one stubborn radiator is rarely the answer we reach for first.
Solid-wall period properties, stone or cob farmhouses and older Devon cottages included, don’t automatically fall into the everything-changes category either. Wall construction affects a room’s heat loss number, which is a sizing input and says nothing on its own about the radiators already inside it. Our post on heat pumps in old stone and cob houses covers what a solid wall does to that number and to pipe routing in a period layout.
The Room-by-Room Survey: Where Your Radiator Schedule Comes From
Room area alone doesn’t tell you the heat loss. Two rooms of the same size lose heat at very different rates depending on wall construction, glazing and how exposed the room is, so a quick estimate built on floor area is still a guess.
What settles it is the £250 plus VAT room-by-room heat loss survey, waived in full if you go ahead with the installation. James measures every room, works out what each one loses, and writes up the design before anything is ordered. It is the same output behind every air source heat pump installation we design, whichever way the radiator question lands on your own house.
Your written design
Worked out room by room, before anything is ordered-
Every room What it loses, worked out from its walls, its glazing and how exposed it is
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Radiator schedule Which radiators change, which stay, and why each one Settled before anything is ordered
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Heat pump The unit, sized to the heat loss the survey measured
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Flow temperature The temperature the system is designed to run at
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Cylinder The hot water cylinder specification
The survey costs £250 plus VAT, waived in full if you go ahead with the installation.
Guess at this stage instead, and both ways it can go wrong cost you. Replace radiators that didn’t need it and you have spent money for nothing. Skip the ones that did and you find out in February, when the room won’t hold its temperature and there is no easy fix mid-winter.
The Microbore Pipework Question for Heat Pump Radiators
Some heating systems, particularly ones installed or extended between the 1960s and 1980s, run on narrow microbore pipe instead of the wider bore standard in modern work. It is a genuine consideration for a heat pump, so it is worth naming directly.
A heat pump needs a higher flow rate than a boiler to move the same amount of heat at a lower temperature, and narrow pipe raises both the water’s speed and the pressure it takes to push it round. Energy Saving Trust’s guidance treats this as a calculation: check the flow velocity a run of microbore would carry, and where a short section falls outside the acceptable range, upgrade just that section.
Why the bore matters to a heat pump
Narrow pipe. The water has to move faster, and it takes more pressure to push it round.
The bore standard in modern work. The same flow of water moves at an easier pace.
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Usually
The numbers already work Checking the flow velocity on the pipework in front of us is all it takes.
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Sometimes
One short section widened Upgrading just that run brings it back into line, with no re-pipe of the whole house.
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Rarely
A full re-pipe Written into your quote before any work starts, never discovered halfway through the job.
What New Radiators for a Heat Pump Cost, and Why We Don’t Guess a Number
We won’t put a figure on this before we have measured your house, and any installer who does is quoting a number with nothing behind it. Guess low and the real quote arrives later as an unwelcome surprise. Guess high and you talk yourself out of a job that would have cost far less than you feared.
No figure until the rooms are measured
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Rooms the survey flags Only the radiators that fall short of what their room needs get counted.From the survey
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What each swap involves How straightforward each change turns out to be, and the type of radiator the room calls for.Room by room
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One line on your fixed quote Written in before you commit to anything, alongside the rest of the installation.Fixed
What we can tell you is the shape of it. A typical home we design for needs some radiators changed, not all of them, and the number the survey settles on goes into your fixed quote alongside the wider cost of an air source heat pump installation in Devon. Nothing about the radiator schedule gets decided after you have said yes.
Frequently Asked Questions
Sometimes, but rarely all of them. A heat pump runs at a lower flow temperature than a boiler, so a room-by-room heat loss survey checks each radiator against what its room actually needs and only changes the ones that fall short.
Book my free home assessmentSome will. A radiator that was already generous for its room at boiler temperature often has enough spare capacity to work at a heat pump’s lower temperature. One that was already close to the limit usually needs a bigger panel in the same position.
Book my free home assessmentTypically 45 to 50°C, against 70°C or higher for a gas or oil boiler. The exact figure for your own system comes out of the heat loss survey, not a fixed industry number.
Book my free home assessmentOften, yes. It comes down to whether the pipe can carry the flow rate a heat pump needs without excessive pressure loss, which we check at the free home assessment. Where a short section falls short, upgrading just that run is usually enough.
Book my free home assessmentIt depends entirely on how many the survey flags and what each room needs, so we don’t quote a figure before we’ve measured. The radiator cost is written into your fixed quote once the survey is done, before you commit to anything.
Book my free home assessmentSometimes, in specific rooms, most often where a floor is already being lifted for another reason. It isn’t the default answer to a radiator that needs upsizing, and we only suggest it where it genuinely suits the room.
Book my free home assessmentNot automatically. Wall construction changes a room’s heat loss number, which affects sizing, but a stone or cob property can need fewer radiator changes than a newer house with poorly sized radiators to begin with. The survey tells you which is true for your own home.
Book my free home assessmentGet a Straight Answer on Your Own Radiators
Guessing from a forum thread or someone else’s quote is how homeowners end up paying for radiators they didn’t need, or getting caught out by ones they did. The free home assessment is where a real answer starts: James walks the property, talks through what heats it now, and gives you a fixed estimate on the spot.
Book my free home assessmentPrefer to talk it through first? Ring 01395 202030. James answers, and he is the person who will price the job.
★★★★★
“James also supported us in organising additional tradespeople whenever needed, making the whole process smooth and stress-free. The house is finally warm, comfortable, and looking much more modern.”
Georgie Stride · Google review
