Yes. In the UK's Electrification of Heat trial, 742 heat pumps were installed across every house type and age band tested, and seasonal performance showed no significant difference between old and new properties — median SPF 2.80. What an old house changes is the heat load, so it needs larger emitters or a higher flow temperature, not a different technology.
Can a heat pump actually work in an old, uninsulated house?
Yes, and this is one of the few questions in the sector with hard monitored evidence behind it. The Electrification of Heat Demonstration Project installed 742 heat pumps into a deliberately broad spectrum of housing types and age bands, including solid-wall Victorian terraces. Its conclusion was that there was no significant difference in seasonal performance by house type or age — where a trained installer judged a property suitable, the age of the building did not determine how well the heat pump performed. The median air source SPF across the trial was 2.80.
That does not mean an old house costs the same to heat. It means the heat pump is not the variable. A leaky building needs more kilowatt-hours whatever produces them.
What does an old house actually change?
| Old-house constraint | What it means for the heat pump | Practical fix |
|---|---|---|
| High heat loss — often 100–160 W/m² against 30–50 in a modern build | Larger unit, larger emitters, higher bill | Cheap fabric measures first, then size honestly |
| Radiators sized for 75 °C flow | Only about 35% of rated output at 45 °C | Upgrade the two or three worst rooms, not all of them |
| 8–10 mm microbore pipework | Flow rate limited at the 5 K ΔT a heat pump needs | 10 mm often workable; 8 mm usually replaced |
| Draughts and single glazing | Comfort complaints get blamed on the heat pump | Draught-proof before commissioning, not after |
| Solid floors, no depth for underfloor | Radiators or fan coils only | Fan-assisted radiators hit output at 40–45 °C |
| Vented cylinder in the loft | Coil usually too small for heat pump charging | Replace with a heat-pump cylinder and a large coil |
Do I have to insulate the whole house first?
No, but the order of work decides the budget. Loft insulation and draught-proofing are the cheapest kilowatts you will ever buy, and doing them before the heat loss survey often drops the heat pump one size and the design flow temperature by several degrees — which compounds into every winter afterwards. Solid wall insulation is a different proposition: it is transformative and expensive, and it is rarely worth doing purely to enable a heat pump. Do the cheap fabric measures, then run a room-by-room heat load calculation on the improved building.
What flow temperature will an old house need?
Realistically 50–55 °C with the original radiators, or 45 °C once the worst rooms are upgraded. Each 5 °C is worth roughly 10–12% of the bill, so the emitter budget is really an efficiency budget — the numbers are in do I need bigger radiators for a heat pump? High-temperature units built on R290 propane or an EVI compressor reach 70–75 °C and allow a genuine like-for-like boiler swap with no emitter work at all, at roughly 30–40% higher running cost. For a listed building where pipework and radiators cannot be touched, that trade is often the right one.
When is a heat pump genuinely the wrong answer?
When there is no lawful or practical position for an outdoor unit, when the electrical supply cannot be upgraded, or when heritage restrictions block both emitter and cylinder work. In those cases a bivalent system — heat pump for most of the year, existing boiler for the coldest days — captures most of the benefit with none of the disruption, and remains fundable in the EU where a standalone fossil boiler is not. Under the EPBD, public support for standalone fossil-fuel boilers ended on 1 January 2025 and Member States must chart a full phase-out by 2040, so the practical question for most older homes is no longer whether the change happens but in which order the work is done. See the EPBD explained for heating.
Frequently asked questions
Do heat pumps work in poorly insulated houses?
Yes. Monitored field trials found no significant difference in seasonal performance between old and new properties. Poor insulation raises the number of kilowatt-hours the house needs, which raises the bill and the equipment size, but it does not stop the heat pump working.
Do I need to insulate before installing a heat pump?
Not as a prerequisite, but cheap measures first save money twice. Loft insulation and draught-proofing typically allow a smaller unit and a lower design flow temperature, and both of those savings repeat every winter for the life of the system.
Can a heat pump replace a boiler without changing radiators?
Only with a high-temperature unit reaching 65–75 °C, and at roughly 30–40% higher running cost than a properly designed 45 °C system. It is a legitimate answer for heritage properties and a poor default anywhere emitters could be enlarged.
Is a hybrid heat pump and boiler better for an old house?
It is a strong compromise where full emitter upgrades are impossible. The heat pump covers most of the season at low flow temperatures and the boiler covers the coldest days, avoiding both the oversizing penalty and the retrofit disruption.