The Okafors have a quote for an air source heat pump on their three bedroom semi, and before signing they want one honest number: what will it cost each year to keep the house warm? Estimating heat pump running costs in the UK rests on two facts about their home, how much heat it soaks up in a year and how many units of heat the pump squeezes out of each unit of electricity. Multiply by the electricity price and the answer drops out.
Below we run their figures at the current Ofgem price cap, compare them with their gas boiler, and look at what moves the bill.
Why one unit of electricity buys several units of heat
Their boiler burns gas. The heat pump instead collects warmth already present in the outdoor air, even on a cold day, and concentrates it, with electricity powering only the fan and compressor. Moving heat takes far less energy than making it.
Engineers express that as a coefficient of performance, or COP. If the pump draws 1 kWh from the meter and delivers 3 kWh into the radiators, its COP is 3. The figure moves around: it rises in mild spells, dips during a hard frost, and drops further whenever the pump has to make very hot water. Because the Okafors care about a whole year, they need the seasonal average, called SCOP. The Energy Saving Trust guidance on air source heat pumps stresses that a carefully designed system running at low flow temperatures does best, and the sums further down show what that is worth in pounds.
Three sums from gas bill to heat pump bill
Mrs Okafor works it out on the back of last year’s statement:
- Find the heat the house really used in a year, in kWh.
- Split that heat by the SCOP to see how much electricity the pump would draw.
- Price that electricity at the unit rate on the tariff.
Their gas statement is the natural starting point, with one adjustment. Some of the gas a boiler burns goes up the flue rather than into the rooms, so the kWh on the bill overstate the heat delivered. Multiply by the boiler’s efficiency to correct it. A tired non condensing model might sit well below 90%, while a healthy modern condensing boiler often gets close to that mark, so 90% is the round figure we use for the main example.
The Okafors’ numbers at the October 2026 cap
Their annual gas use happens to match Ofgem’s typical figure for a medium home: 11,500 kWh. With a boiler converting 90% of that into warmth, the house needs roughly 10,350 kWh of heat a year for radiators and hot water combined.
Between 1 October and 31 December 2026, paying by direct debit, the Ofgem energy price cap limits electricity to 26.32p per kWh and gas to 7.97p per kWh. Holding those prices for twelve months gives this picture:
| Heating system | Energy used a year | Unit rate | Yearly energy cost |
|---|---|---|---|
| Gas boiler (90% efficient) | 11,500 kWh gas | 7.97p | £916.55 |
| Heat pump, SCOP 2.5 | 4,140 kWh electricity | 26.32p | £1,089.65 |
| Heat pump, SCOP 2.8 | 3,696 kWh electricity | 26.32p | £972.90 |
| Heat pump, SCOP 3.0 | 3,450 kWh electricity | 26.32p | £908.04 |
| Heat pump, SCOP 3.5 | 2,957 kWh electricity | 26.32p | £778.32 |
| Heat pump, SCOP 4.0 | 2,588 kWh electricity | 26.32p | £681.03 |
Their installer has promised a SCOP of 3.0. Splitting 10,350 kWh by 3 gives 3,450 kWh from the meter, and at £0.2632 each that is £908.04 a year, close to £76 a month. Plug in panel heaters instead, which turn each kWh into exactly one kWh of heat, and the full 10,350 kWh would be bought at the electricity price, roughly £2,724.
The table makes the tipping point plain. With electricity priced at just over three times gas, a pump hitting a SCOP near 3 runs at about the same cost as a good boiler. Fall short of that and the pump is dearer; beat it and each extra point of efficiency saves real money.
The daily charges that can tip the balance
Units are not the whole story. The same October to December 2026 cap sets a daily standing charge of 54.83p for electricity and 29.68p for gas. The electricity one stays whatever the Okafors heat with, but if the heat pump lets them have the gas meter removed, the gas one goes for good.
A year of the gas charge is about £108.33. Add that to the boiler’s £916.55 and gas costs them £1,024.88, against £908.04 for a SCOP 3.0 pump, so the near draw becomes a saving of around £117 a year. There is a catch: their gas hob. Keep it, and they keep paying the gas standing charge, which wipes the saving out. To see standing charges and unit costs together, they run both options through our energy bill calculator before comparing tariffs.
Four things that push the bill up or down
How hot the radiator water runs
Nothing matters more than flow temperature, meaning how warm the water leaving the pump is. Cooler water lets the pump work more efficiently, which is why installers so often swap in bigger radiators or lay underfloor pipes: more surface area keeps rooms comfortable at a gentler water temperature. A system planned around 35°C to 45°C will normally outperform one pushed to 55°C or above.
How fast the house leaks heat
Every kWh the pump supplies is replacing warmth escaping through roof, walls and gaps. Topping up loft insulation, filling cavity walls and sealing draughts lowers the yearly heat demand, and the running cost falls by the same proportion. Cut the heat loss in half and the bill halves too, at any SCOP.
What each kWh costs
Since the bill is just kWh used times price per kWh, a lower rate feeds straight through. Several suppliers sell tariffs built for heat pump homes with cheaper hours, and choosing well can matter as much as the equipment. The Okafors compare actual pence per kWh rather than marketing claims, using our kWh cost calculator to price 3,450 units at each rate on offer.
The hot water cylinder
Raising a cylinder to 50°C or more asks more of the pump than warming radiators does, so efficiency dips during each hot water cycle. With two teenagers taking long showers, the Okafors should expect a slightly lower year round SCOP than a couple would get.
A second case: the neighbours’ smaller house
Next door, a well insulated two bedroom home burned 8,000 kWh of gas last year through an 85% efficient boiler. Its heat demand is therefore 8,000 × 0.85, or 6,800 kWh. A well designed pump reaching a SCOP of 3.5 would need about 1,943 kWh of electricity, which at 26.32p comes to around £511 a year.
Their existing bill for that heat is 8,000 kWh at 7.97p, £637.60, plus about £108.33 of gas standing charge that would disappear with the meter. That makes £745.93 against £511, a gap of roughly £235 a year. They also have panels on the roof, so part of the pump’s daytime demand could be covered for free, and our solar panel calculator gives a feel for how much of that generation they might use themselves.
Key points
- Yearly cost is heat demand split by SCOP, then priced at the electricity rate: 10,350 kWh at SCOP 3 is £908.04.
- On October 2026 cap unit prices, a SCOP near 3 breaks even with a 90% efficient boiler.
- Having the gas meter removed saves about £108 a year in standing charges.
- Flow temperature, insulation and tariff choice outweigh the make of pump.
- Cap prices are reset each quarter, so redo the sums whenever they change.
Frequently Asked Questions
My installer quotes a SCOP of 3. Will I spend less than on my gas boiler?
On unit prices alone it is roughly a draw: £908.04 against £916.55 for a 90% boiler at the October 2026 cap. The pump only pulls clearly ahead if you also drop the gas supply and its standing charge.
My quote says SCOP 2.8. Is that a poor design?
It is below the 3 or more that a well planned air source system should aim for, and in our example it costs £972.90 a year. Ask whether larger radiators could lower the flow temperature.
Roughly how many kWh will the pump take from my meter each day?
Split yearly heat demand by SCOP, then by 365. For 10,350 kWh at SCOP 3 that averages about 9.5 kWh a day, with January days far above that and July days far below.
We are out at work all day. Should we switch the pump off?
Generally no. A pump is happiest ticking over at low temperature, and a cold house forces a hard, inefficient reheat in the evening. A modest setback of a degree or two usually beats switching off.
The Okafors now have a figure they trust: about £908 a year at a SCOP of 3, and a clear view of what would push it lower. Start from your own gas or heat use, a realistic SCOP and the tariff you would really pay, and your estimate will beat any national average.