How the calculation works
Comparing an oil boiler with a heat pump on price per unit is misleading, because they turn energy into heat at very different efficiencies. So the calculator starts from the heat your home actually uses.
1. Heat delivered by your oil. Heating oil (kerosene) holds about 10.35 kWh of energy per litre. A modern condensing boiler turns roughly 85–90% of that into heat in your radiators; an older non-condensing boiler can be closer to 75%.
2. Electricity the heat pump needs. A heat pump's seasonal coefficient of performance (SCOP) tells you how many units of heat it makes for every unit of electricity, averaged over a heating season.
3. What that electricity costs. If part of your heating runs on a cheap overnight rate, or from a battery you charged cheaply, the calculator blends the two rates by the share you enter. Annual servicing is added to both sides.
4. Payback. The net install cost, after any grant, divided by the annual saving.
What makes the biggest difference
Flow temperature and SCOP
SCOP is the number that swings the result most. The lower the water temperature your radiators need, the more efficient the heat pump. As a rough guide, a system designed around a 50°C flow might manage a SCOP near 3, while one running at 35–40°C can reach 4 or more. Larger radiators or underfloor heating let you run cooler water, which is why radiator upgrades often matter more than the heat pump brand.
Your electricity tariff
On a standard flat rate, a heat pump's running cost can end up close to oil. A time-of-use tariff, pre-heating the house and the hot water cylinder in cheap hours, or a home battery all push the blended rate down. Try changing the "share run on cheap rate" field to see the effect.
Sizing
The calculator gives a rough heat load by dividing your annual heat by 2,000 hours. That is only a sanity check. A proper room-by-room heat loss survey, which MCS installers must carry out, is what sizes the unit. An oversized heat pump turns on and off more often and loses efficiency; an undersized one leans on a backup immersion heater.
Grants
In England and Wales, the Boiler Upgrade Scheme gives a grant towards an air source heat pump installed by an MCS-certified installer. The installer claims it and takes it off your quote. Check the current amount and eligibility on GOV.UK, then enter your net cost after the grant.
Frequently asked questions
Is a heat pump cheaper to run than oil?
It depends mainly on your heat pump’s efficiency (SCOP), your electricity rate and the oil price. With a good SCOP and some heating on a cheap overnight rate, a heat pump is usually cheaper. On a flat electricity tariff with a poorly designed system, it can cost about the same or more. Enter your own figures above to see your case.
How many kWh are in a litre of heating oil?
Kerosene heating oil holds roughly 10.35 kWh per litre. How much of that reaches your radiators depends on your boiler’s efficiency, typically 75–90%.
What SCOP should I use?
Use the figure from your installer’s design for the flow temperature they plan to run. Without one, 3.0 is a cautious estimate for radiators at around 50°C and 3.5–4.0 for a well-designed low-temperature system.
What is a break-even oil price?
It is the oil price at which oil heating and the heat pump would cost the same per year, given your other inputs. If oil is above that price, the heat pump saves money.
Does the calculator include the cost of new radiators?
Only if you include them in the install cost field. Enter the total you will actually pay, after any grant.