Boiler Running Cost Calculator
Estimate what your boiler really costs to run. Enter the power, efficiency, unit rate and hours of use to see daily, monthly and yearly heating costs.
Condensing combi/system boiler
Monthly running cost
About £9.33 a day · £3,407 a year
Usage breakdown
| Period | Fuel used | Cost |
|---|---|---|
| Per hour | 26.7 kWh | £1.87 |
| Per day | 133.3 kWh | £9.33 |
| Per week | 933.3 kWh | £65.33 |
| Per month | 4,000 kWh | £280.00 |
| Per year | 48,666.7 kWh | £3,406.67 |
Costs assume the boiler runs at full power for the hours entered. Real boilers cycle on and off, so actual use is usually lower.
Quick tips
- • A modern condensing gas boiler is around 90% efficient; older ones can be 70% or less.
- • Electric boilers are ~100% efficient but electricity costs far more per kWh than gas.
- • Lowering your flow temperature can improve a condensing boiler's real-world efficiency.
- • Use the unit rate from a recent energy bill for the most accurate result.
Typical unit rates (per kWh)
Good to know
Results are estimates based on running at full power. A boiler heating water or a room will modulate and cycle, so true consumption depends on demand, insulation and weather. Always check your latest bill for current rates.
About the Boiler Running Cost Calculator
The Boiler Running Cost Calculator turns your boiler's power rating into a real, money figure. By combining the boiler's heat output in kilowatts (kW), its efficiency, your energy unit rate and how many hours a day it runs, it shows what you spend per hour, day, week, month and year — plus how much fuel you burn along the way.
Boilers are rated in kW of heat output, but they never turn all of their fuel into useful heat. A boiler that is 90% efficient needs about 1.11 kWh of gas to deliver 1 kWh of heat; the other 10% is lost. The calculator works backwards from output to the fuel you actually pay for, so a less efficient boiler correctly shows a higher running cost. It supports mains gas, electricity, LPG and heating oil, each with typical default rates you can override with figures from your own bill.
How to Use the Boiler Running Cost Calculator
- 1 Pick your fuel type — gas, electric, LPG or oil. This sets a typical unit rate and efficiency you can adjust.
- 2 Enter the boiler power (kW) — find it on the boiler's data plate or manual. Most domestic combi boilers are 24–35 kW.
- 3 Set the efficiency and unit rate — use your boiler's efficiency rating and the price per kWh from a recent energy bill.
- 4 Choose hours used per day with the quick chips or type your own, and add a daily standing charge if you want the full bill.
- 5 Read your results — daily, monthly and yearly costs and the full usage breakdown update automatically as you type.
Frequently Asked Questions
How much does it cost to run a boiler per hour? +
At full power, a 24 kW gas boiler that is 90% efficient burns about 26.7 kWh of gas an hour. At a 7p/kWh unit rate that's roughly £1.87 per hour of continuous firing. In practice boilers cycle on and off, so the real hourly cost over a day is usually much lower than the full-load figure.
Should I use the boiler's kW heat output or input? +
Enter the heat output (the headline kW figure on most boilers) and set the efficiency. The calculator divides output by efficiency to work out the fuel input you actually pay for. If you only know the gross input rating, enter that and set efficiency to 100% to cost the raw fuel.
Why is an electric boiler more expensive to run than gas? +
Electric boilers are nearly 100% efficient, but electricity typically costs around three to four times more per kWh than mains gas. Even though almost no energy is wasted, the higher unit rate usually makes electric heating more costly to run than a modern gas boiler.
How many hours a day does a boiler actually run? +
It varies a lot. In winter, central heating might be on for 6–10 hours but the burner only fires for part of that time as it cycles to maintain temperature. A good estimate is the number of hours of effective full-power heating, which is often 2–5 hours of equivalent run time per day.
Does this include the standing charge? +
Only if you add one. The standing charge is a fixed daily fee from your supplier that applies whether or not you use the boiler. Enter your daily standing charge to fold it into the daily, monthly and yearly totals, or leave it at zero to see fuel costs alone.