This comparison is one division done twice. What a delivered kilowatt hour costs from each fuel, and what fraction of it reaches the room. Everything else in the argument is downstream of those two numbers.
DESNZ Quarterly Energy Prices / QEP 4.1.1 standard grade burning oil / published 27 August 2026 / checked 23 September 2026 / lag 27 daysone to four weeks oldtier A
Typical price for a delivery of up to 1,000 litres, VAT at 5% included. Observed on the Monday nearest the 15th.
Cost per useful kilowatt hour
| System | Unit price | Conversion | Cost per useful kWh |
|---|---|---|---|
| Kerosene boiler, 90% | 90.01p a litre | 10.452 kWh a litre | 9.57p |
| Kerosene boiler, 75% | 90.01p a litre | 10.452 kWh a litre | 11.48p |
| Heat pump, SCOP 3.0 | 22p a kWh, illustrative | 3.0 kWh out per kWh in | 7.33p |
| Heat pump, SCOP 2.5 | 22p a kWh, illustrative | 2.5 kWh out per kWh in | 8.8p |
| Heat pump, SCOP 2.0 | 22p a kWh, illustrative | 2.0 kWh out per kWh in | 11p |
Read the table as a threshold rather than a verdict. At 22p electricity, the heat pump crosses below oil somewhere around a seasonal efficiency of 2.3. If your tariff is lower, the threshold falls. If it is higher, the threshold rises and can move out of reach of a retrofit.
The equipment does not decide this. The tariff and the fabric decide it.
The nineteen year old boiler case
An old non-condensing boiler running near 75% pushes oil heat to 11.48p a useful kilowatt hour. That closes some of the gap on its own, and it is worth noticing that the cheapest option on that comparison is often a modern condensing oil boiler rather than either extreme.
What the grant does and does not do
The Boiler Upgrade Scheme is a capital grant, applied for by the installer, that reduces what you pay to have the system fitted. It does not change the running cost by a single penny. Any quote that presents the grant as making the heat pump cheaper to run is mixing two different accounts.
The solid wall problem
A heat pump achieves its rated efficiency at low flow temperatures. Existing radiators sized for a 70 degree flow will not deliver enough heat at 45 degrees in a leaky house, so either the radiators grow or the flow temperature rises and the efficiency falls. In a solid wall cottage that is not an optional extra, it is the project.
This page uses an illustrative electricity rate rather than a reading, because domestic electricity tariffs are set per household and no single published figure would be right for you. Everything else on this page comes from the readings.
Primary sources for this page
- Ofgem Boiler Upgrade SchemeGrant scheme for heat pump and biomass installations in England and Wales. Applications are made by the installer.
- DESNZ Quarterly Energy Prices, table 4.1.1Monthly typical retail price of standard grade burning oil, the fuel sold to UK households as kerosene. Priced on the Monday nearest the 15th of the month, for deliveries of up to 1,000 litres, VAT at 5% included. This is the only official UK-wide domestic heating oil price series.
- NEEP cold climate air source heat pump product listPerformance data at low ambient temperature, used instead of a manufacturer headline COP.
- OFTECTrade body for the UK oil heating industry. Registration scheme for technicians. Cited for installation practice, not for prices.