EPC ratings and heat pumps
A heat pump usually improves the rating, but by less than the price tag suggests — around 6 SAP points on a home with a working gas boiler. The reason is that SAP prices electricity well above gas.
Last reviewed 24/09/2026
This is one of the most common disappointments in domestic retrofit: a household spends £9,000 to £14,000 on an air source heat pump, orders a new EPC, and finds the band has not moved.
It is not a fault in the installation and it is rarely a fault in the assessment. It is how SAP works.
Why the gain is small
SAP scores a property on modelled running cost. A well designed heat pump delivers roughly three units of heat for every unit of electricity it consumes — a seasonal performance factor of around 3. That sounds decisive until you look at the fuel prices in the model: electricity costs substantially more per kilowatt hour than mains gas, and that gap eats most of the efficiency advantage.
The result on a property with a working condensing gas boiler is a gain of a few points — around 6 in our cost model — for the most expensive measure on the list. At roughly £1,900 per SAP point, it is around ninety times the cost per point of insulating a hot water cylinder.
Where heat pumps do move the band
- Properties on electric storage heaters or electric room heaters, where the improvement is dramatic and often worth several bands.
- Properties off the gas grid running on oil or LPG.
- Well insulated properties where the heat pump runs at a low flow temperature and achieves a high seasonal efficiency.
- Properties with solar PV, where some of the electricity is generated on site.
Fabric first, and not only for the certificate
A heat pump in a poorly insulated house has to run at a higher flow temperature to keep up, which lowers its efficiency, raises bills and scores worse. The same insulation that earns cheap SAP points — loft to 270 mm at £100 to £350, cavity walls at £600 to £1,800 — is also what makes a heat pump work properly.
Doing the fabric first is therefore not a delaying tactic. It changes the specification of the heat pump you need, often reduces its size and cost, and improves the number it eventually scores.
If the goal is band C by 2030
For a private rented property that must reach band C by 1 October 2030, a heat pump is usually the wrong first move. The £10,000 cost cap is per property, and a heat pump can consume the entire cap while delivering fewer points than £2,000 of insulation.
Work through the cheap measures first, re-assess, and only then decide whether anything expensive is still needed. That also preserves the evidence trail if the property does end up at the cap and you need to register an exemption.
Can a heat pump lower the rating?
It can, though it is unusual. On a poorly insulated property replacing an efficient gas boiler, the modelled running cost can rise enough to cost a point or two. It is more common for the score to stay flat than to fall.
If that happens, the honest reading is that the property needs fabric work, not that the heat pump was a mistake — the carbon position improves either way, and SAP is a cost model rather than a carbon model.
Grants and what they change
Grants change what you pay, not how the property is assessed. A heat pump installed with grant support scores exactly the same as one paid for in full.
Households on qualifying benefits in bands D to G may be able to have heating and insulation funded under ECO4, which runs to 31 December 2026. Where ECO4 applies it usually funds a package rather than a single measure, which is a better outcome than a heat pump on its own.
What to ask an installer
- What seasonal performance factor is the design based on, and at what flow temperature?
- What fabric work is assumed in that design?
- Are the existing radiators adequate at that flow temperature, or are they being replaced?
- Will a new EPC be lodged after the work, and is it included in the price?