Heat Pumps: What You Need to Qualify and What They Cost to Run
Insulation standards, radiator sizing, outdoor space and hot water storage — what a heat pump survey checks, plus how running costs compare to gas.
Key takeaways
- Efficiency depends on flow temperature — bigger radiators mean lower bills.
- You need outdoor space for the unit and indoor space for a hot water cylinder.
- Insulation and draught-proofing come first; they change the required unit size.
- Pairing with solar and a battery materially reduces running cost.
What the survey actually checks
A proper heat loss calculation is done room by room to specification standards. It determines the unit size and whether your existing radiators can deliver enough heat at a low flow temperature. Undersized radiators are the most common reason a heat pump underperforms.
- Room-by-room heat loss survey (not a rule-of-thumb sizing).
- Radiator or underfloor emitter capacity at 45–50°C flow.
- Outdoor space with airflow clearance and acceptable noise siting.
- Room for a hot water cylinder, usually 180–250 litres.
- Adequate loft and cavity insulation, and draught-proofing.
Running costs versus gas
A heat pump delivers roughly 3–4 units of heat per unit of electricity (its seasonal coefficient of performance). Because electricity costs more per unit than gas, that efficiency is what makes the comparison work — and it collapses if the system is forced to run at high flow temperatures.
Households on a heat-pump-specific tariff, or generating their own solar, see the strongest results.
Solar, battery and heat pump together
Solar output is lowest in the depths of winter when heat demand peaks, so solar will not run your heat pump in January. What it does do is cover a large share of shoulder-season and hot-water demand, while a battery lets you buy heating electricity at off-peak rates. Modelled together, the combined payback is usually better than either technology alone.
Frequently asked questions
Do I need to replace all my radiators?
Usually not all. A survey typically flags a handful that need upsizing to run at lower flow temperatures.
Are heat pumps noisy?
Modern units are comparable to a fridge at a few metres. Siting rules cover noise at the neighbouring property boundary.