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James visits, gives a straight answer on suitability and a fixed estimate on the spot.
Yes, a heat pump in an old house can work well, stone and cob included, along with the solid-wall properties that make up a lot of Devon’s older housing stock. The building’s age and its wall material go into the design as inputs. What decides the outcome is whether that design starts from the property’s measured heat loss, room by room, or from a generic size chart, or never starts at all because the walls fail a modern checklist.
Key Takeaways
- A heat pump can heat a solid stone or cob Devon house properly when it is sized to a room-by-room heat loss survey instead of a generic chart.
- Since April 2026 a valid EPC is no longer strictly required to apply for the Boiler Upgrade Scheme, which clears a real blocker for older properties.
- Off-gas-grid oil and LPG homes can qualify for £9,000 on applications made up to 31 March 2027, and other eligible homes for £7,500.
- Solid walls lose heat faster than a modern cavity wall, and that changes the unit size and the radiator numbers on the design.
- A heat pump typically runs at 45 to 50°C against a boiler’s 70°C plus, so the survey checks every radiator and changes only the ones it flags.
- If an installer has called your period property unsuitable, treat that as a sizing opinion until someone measures the heat loss room by room.
Homeowners tell James they have already been round the houses: one company wanted to sell them a unit twice the size they needed, another said the property “wasn’t suitable” and left it there. Both answers usually come from the same shortcut, sizing a heat pump off a rule of thumb instead of measuring the building.
Do Heat Pumps Actually Work in Old Devon Houses?
They do, and the evidence goes well past theory. Norway has some of the highest heat pump adoption rates in the world, through winters far colder than Devon ever sees, so cold air is a smaller obstacle than people assume. For an old house, the question that matters is whether anyone measured the building before picking a unit.
Where the “can’t be done” answer comes from
A heat pump runs at a lower flow temperature than an oil or gas boiler, and on a poorly sized system that lower temperature feels lukewarm in a draughty room.
45 to 50°C
Typical heat pump flow temperature. An oil or gas boiler runs at 70°C plus.
The fault there sits with the sizing. It happens on modern houses too, less often, because a modern house is more forgiving of a rough estimate.
James works as a freelance MCS assessor for NAPIT, auditing other installers’ finished jobs alongside running his own. In older properties the pattern he meets most often is a unit sized off a rule of thumb: oversized, so it short-cycles, or undersized, so the house never quite gets warm. A room-by-room heat loss survey, the process behind every job we design, takes the guesswork out on both sides.
The April 2026 Change That Unblocks a Lot of Old Devon Houses
Paperwork used to be a problem of its own, separate from the technical one. Before 28 April 2026, a Boiler Upgrade Scheme application needed a valid Energy Performance Certificate on the property before an installer could even submit it.
EPC first, grant second
- Certificate A valid EPC on the property before anything else
- Your part Book an assessor, then wait on the certificate
- Application Submitted only once the certificate arrived
Apply without a current EPC
- Certificate No longer strictly required
- Your part A recent utility bill and photos of the heating you have now
- Application Goes in on that evidence where no current EPC exists
Plenty of older Devon properties, from the cob cottages and stone farmhouses around Silverton to the rest of the county, never needed an EPC or hold one that is years out of date. For them, that change removes a real hold-up.
The paperwork change leaves the value of the grant alone. Off-gas-grid homes on oil or LPG can qualify for £9,000 on applications made up to 31 March 2027, and other eligible homes, mains gas included, can qualify for £7,500. Both apply to owner-occupiers in England and Wales replacing a fossil fuel or direct-electric system, and eligibility turns on the property and your circumstances. Our guide to the £9,000 rate for off-grid oil and LPG homes sets out the rules and the cut-off in full.
What Solid Stone and Cob Walls Do to a Heat Pump’s Heat Loss Number in an Old House
Solid walls, stone or brick, lose heat faster than a modern cavity wall, and cob sits partway between. None of that rules a heat pump in or out. Each fact moves the heat loss number, and that number is what the system gets sized to.
Solid stone or brick
A solid wall loses heat faster than a modern cavity wall. That pushes the heat loss number up, and the survey sizes the unit, cylinder and radiators to the higher figure.
Loses heat fasterThick cob
Sheer mass gives a thick cob wall more built-in resistance than a thin solid brick wall of the same era. It still gets measured room by room. The old school at Cheriton Fitzpaine is cob and rubble under thatch, thought to be the longest thatched building in Great Britain, and our Cheriton Fitzpaine installation page shows how we survey and design for that kind of house.
A partial exceptionLoft insulation and glazing
A property with poor loft insulation and single glazing needs a larger, more expensive system than the same house with the basics done, and James says so at the assessment. He works it into the survey, and you never have to clear it before he will quote.
A design inputSome installers push wall or loft insulation as a precondition before they will even quote, treating every solid-wall property the same whatever the survey says. We work the other way round: James measures the heat loss room by room and designs to it. A cob house with good loft insulation and a stone farmhouse with none can need different specifications, and only the survey shows which is which.
Radiators: Why Guessing Costs More Than Measuring
A heat pump sends cooler water round the system than a boiler, and a radiator fed cooler water gives out less heat than its rating suggests. That explains why older properties get told they “need all new radiators”. In practice it is a room-by-room question, and the answer usually lands somewhere in the middle.
Retrofitting underfloor heating purely for a heat pump is rarely the first answer James reaches for.
Guess at this stage and you either pay for radiators that never needed changing or find out in February that a couple of rooms fall short. The heat loss survey produces the radiator schedule alongside the flow temperature and the cylinder specification, so every change is settled before work starts instead of discovered on site.
Pipe Routes and Cylinder Siting in a Period Layout
Older properties rarely come with the neat, purpose-built airing cupboard of a 1990s house. That shapes two decisions a modern build barely has to think about: where the cylinder goes, and how the pipe reaches it.
Three things James checks on the walk round
Where the cylinder goes
A heat pump cylinder is larger and better insulated than most existing tanks, and in a stone or cob house the airing cupboard is often the only realistic spot, so James measures it instead of assuming.
How the pipe gets there
The further the outdoor unit sits from the cylinder, the more pipe, insulation and labour it takes to join the two, and thick stone or cob walls leave fewer easy places to route a new run between them.
Listed or conservation area
Listed status typically removes the automatic permitted development right most homes have, so on a listed property or in a conservation area, siting the outdoor unit can need a look at the rules first.
Each of these is a reason to walk the property before anyone quotes a price, and that walk is what the free home assessment is for.
Three Installers, Three Answers: What the Street, Somerset Job Taught Us
One job outside our own patch shows the pattern clearly. A homeowner in Street, Somerset, on an ageing oil boiler, had three companies through the door before calling us, two of them national names, and the advice contradicted itself from one visit to the next. Faced with opposite answers from people meant to be the experts, they had lost confidence in the whole process.
What the homeowner heard, and what the survey found
Fit a 16kW heat pump
An opinionNot suitable for a heat pump at all
An opinionSuitable, and well under 16kW
MeasuredJames specified against the real number, upgraded only the radiators the survey flagged as undersized, and fitted an Ideal Logic Air with the Boiler Upgrade Scheme grant applied at the rate in force at the time. The job ran to about a week on site, in line with how we schedule every air source heat pump installation: one or two properties at a time, so James stays involved throughout.
Street was never a hard house. “Not suitable” and “you need a 16kW unit” were both opinions until somebody measured the building, and James applies the same test to any stone, cob or older Devon property, and to other installers’ work when he audits it as an MCS assessor. If yours still runs on oil, our guide to converting from oil to a heat pump covers how that switch works in practice.
Frequently Asked Questions
Yes, when the system is sized to a room-by-room heat loss survey instead of a generic chart. The wall material changes the heat loss number, and the unit, cylinder and radiators are sized to that number.
Book my free home assessmentNo, not as a precondition. Insulation affects the heat loss number and therefore the specification. We account for it at the survey stage, and you do not need to finish it before we will quote.
Book my free home assessmentNo, not since the scheme’s regulations changed in April 2026. A valid EPC is no longer strictly required; where a property has no current one, alternative evidence such as a recent utility bill and photos of the existing heating system can be used instead.
Book my free home assessmentSome, possibly, but rarely all of them. A heat pump runs cooler water than a boiler, so some radiators may need upgrading while others already have enough capacity. The heat loss survey produces a radiator schedule that shows exactly which is which.
Book my free home assessmentThrough a room-by-room heat loss survey, which calculates what each room loses and sizes the unit, cylinder and radiators to that figure instead of to the property’s age or a rule of thumb.
Book my free home assessmentNot necessarily. A “not suitable” verdict is often a sizing opinion with no measurement behind it. A room-by-room heat loss survey gives a definitive answer for your own property.
Book my free home assessmentGet a Straight Answer on Your Own Property
Every stone, cob or period house behaves differently, and only a measurement shows where yours lands. The free home assessment is where that starts: James walks the property, asks what heats it now, and gives a straight answer on suitability with 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.
★★★★★
“The heat pump is almost silent, which was something we were worried about, and the results have been fantastic. We’re lovely and warm and always have plenty of hot water.”
Grace Murphy · Google review
