A gas boiler’s running cost depends on how much gas it uses and the price you pay for that gas. To calculate the cost, multiply the gas consumed in kilowatt-hours (kWh) by your tariff’s unit rate. For example, using 20kWh of gas at an illustrative price of 7p/kWh would cost £1.40.
However, a boiler doesn’t necessarily use gas at its maximum rated output for every hour the heating is switched on. Its consumption changes according to the heat your home needs, the boiler’s settings and how the system operates. This means a 30kW boiler won’t automatically cost the equivalent of 30kWh of gas every hour.
How much does a gas boiler cost to run per hour?
The table below shows what different levels of gas consumption would cost over one hour.
| Gas used in one hour | Cost at 7p/kWh |
| 5kWh | £0.35 |
| 10kWh | £0.70 |
| 15kWh | £1.05 |
| 20kWh | £1.40 |
| 25kWh | £1.75 |
| 30kWh | £2.10 |
These figures use an illustrative gas price of 7p/kWh, not a current national average. Check your latest energy bill or supplier account for your actual unit rate.
The table also assumes that the stated amount of gas is consumed during the hour. It doesn’t mean that a boiler with a particular kW rating will necessarily use that amount of gas.
For example, if your boiler consumes 10kWh of gas during an hour, the cost at 7p/kWh is 70p. If it consumes 20kWh, the cost is £1.40.
The calculation is:
Gas consumed (kWh) × unit rate (£/kWh) = gas cost
Does a 30kW boiler use 30kWh of gas every hour?
No. A boiler’s advertised kW rating is generally its maximum heat output, not a statement of how much gas it consumes continuously.
A 30kW boiler can produce up to approximately 30kW of useful heat under its rated conditions, but the amount of gas required depends on its efficiency. It may also operate at a lower output when the home needs less heat.
For example, a boiler with a maximum useful output of 30kW and an assumed efficiency of 90% would need approximately 33.3kW of gas input to produce that output.
At an illustrative gas price of 7p/kWh, operating at that input continuously for one hour would cost approximately £2.33.
However, this is a theoretical example rather than a prediction of what a particular boiler will cost to run. Modern boilers can reduce their output, and heating demand changes throughout the day.
A boiler may also stop firing once the required temperature has been reached and restart when more heat is needed. Consequently, one hour with the heating switched on isn’t necessarily one hour of continuous gas consumption at maximum output.
How much does a gas boiler cost to run per day?
Daily costs depend on the amount of gas used rather than simply how many hours the heating is enabled.
For example, at an illustrative rate of 7p/kWh:
| Daily gas consumption | Cost at 7p/kWh |
| 20kWh | £1.40 |
| 40kWh | £2.80 |
| 60kWh | £4.20 |
| 80kWh | £5.60 |
| 100kWh | £7.00 |
These are examples, not typical daily consumption figures. A small, well-insulated home may use considerably less gas than a large, poorly insulated property during cold weather.
If your heating is scheduled for eight hours, you shouldn’t simply multiply the boiler’s maximum output by eight. The boiler may operate at different outputs or stop firing during that period.
The most useful way to estimate your daily cost is to look at how much gas your household actually uses over a representative day.
How much does a gas boiler cost to run per month?
Monthly running costs can vary substantially between summer and winter.
During colder months, the boiler may need to provide heating for longer periods and replace more heat lost through the building. In summer, a household with a combi boiler may use gas mainly for hot water.
For example, if your household uses 1,000kWh of gas during a month:
1,000kWh × £0.07 = £70
At 9p/kWh, the same consumption would cost £90.
These figures exclude the standing charge and assume that all the gas consumption is included in the calculation. If you also have a gas cooker or another gas appliance, your household’s total gas consumption can’t be attributed entirely to the boiler.
How much does a gas boiler cost to run per year?
The most reliable starting point is your actual annual gas consumption.
Your energy bill or supplier account should show how much gas you’ve used over a period, measured in kWh. You can use this to estimate your annual cost at your current tariff.
| Annual gas consumption | Cost at 7p/kWh |
| 5,000kWh | £350 |
| 7,500kWh | £525 |
| 10,000kWh | £700 |
| 12,500kWh | £875 |
| 15,000kWh | £1,050 |
| 20,000kWh | £1,400 |
Again, these are illustrative consumption levels rather than estimates for particular property sizes.
For example, if your household uses 12,000kWh of gas annually and your unit rate is 8p/kWh, the gas itself would cost:
12,000 × £0.08 = £960
You would then need to account for the standing charge and any other applicable charges to estimate your total gas bill.
Using actual annual consumption is generally more useful than multiplying a winter day’s usage by 365, because heating demand changes considerably throughout the year.
What about the gas standing charge?
The standing charge is separate from the cost of the gas you consume.
It’s a daily charge associated with having a gas supply, and you generally pay it even if you don’t use any gas that day.
For that reason, it shouldn’t normally be included when calculating the additional cost of running your boiler for an hour.
However, if you’re estimating your total annual gas bill, you should include it:
Annual gas cost = gas consumption × unit rate + daily standing charge × 365
For example, if your standing charge were 30p per day, it would add £109.50 over a year.
How to calculate your actual gas boiler running costs
Using your own consumption data will give you a more useful estimate than relying on a boiler’s maximum output.
1. Find your gas unit rate
Check your latest energy bill or supplier account for the price you pay per kWh.
2. Find your gas consumption
Your bill should show gas consumption in kWh. A smart meter or supplier app may also provide daily or more detailed usage information.
If you’re using a traditional gas meter, remember that the meter may record volume rather than energy. Gas suppliers convert meter readings into kWh using the gas’s calorific value and other prescribed factors.
3. Multiply consumption by your unit rate
For example, if you use 50kWh of gas and pay 8p/kWh:
50 × £0.08 = £4.00
This gives you the cost of the gas consumed, excluding the standing charge.
4. Compare representative periods
A single day may not tell you very much. Compare several days with similar weather and heating schedules, or use monthly and annual consumption for a broader picture.
If you want to estimate heating-only consumption, remember that your meter may also include gas used for hot water and cooking.
What affects gas boiler running costs?
Home size and insulation
A larger home generally requires more heat than a smaller one, while poor insulation and draughts allow heat to escape more quickly.
Improving insulation and reducing unwanted draughts can reduce the amount of heat your boiler needs to replace.
Outdoor temperature
The colder it is outside, the more heat your home is likely to lose. This is why gas consumption often rises substantially during winter.
Thermostat settings
Higher indoor temperatures generally require more energy to maintain. Setting the thermostat to a comfortable temperature rather than unnecessarily high can help reduce consumption.
Heating schedules
Heating an empty home for longer than necessary can waste energy. Suitable schedules and controls can help match heating to when rooms are actually needed.
Boiler efficiency
A more efficient boiler converts a greater proportion of the gas’s energy into useful heat.
Modern condensing boilers recover heat from combustion gases that would otherwise be lost, helping them operate more efficiently than older non-condensing appliances.
Flow temperature
The flow temperature is the temperature of the water sent from the boiler to your radiators.
On suitable condensing systems, reducing an unnecessarily high flow temperature can improve efficiency by allowing the boiler to recover more heat from its combustion gases. However, the setting still needs to be high enough to heat the home adequately.
Hot-water use
If you have a combi boiler, it also uses gas to produce hot water when required. Longer showers and greater hot-water demand can therefore increase gas consumption even when the central heating is off.
Does a larger boiler cost more to run?
Not necessarily.
A 35kW boiler doesn’t automatically consume more gas than a 24kW boiler in the same home simply because it has a higher maximum output.
The home’s heat demand is an important factor. If two suitable boilers are supplying the same amount of useful heat, their gas consumption will depend largely on their efficiency and how they operate at that demand.
A larger boiler may also have a higher maximum output primarily to provide domestic hot water. For example, a combi boiler may need substantial output to heat water quickly for a shower, while its central-heating output can be considerably lower.
This is why comparing boilers solely by their headline kW rating can be misleading.
The important questions are whether the boiler is appropriately sized for the property, how efficiently it operates and how much heat the home actually needs.
How can you reduce gas boiler running costs?
The most effective approach is usually to reduce unnecessary heat demand and make sure your heating system is operating efficiently.
Use your heating controls effectively. Set schedules around when you need heating and avoid heating unused rooms unnecessarily. Smart controls can make it easier to adjust schedules when your plans change.
Improve insulation and draught-proofing. Reducing heat loss means the boiler has less work to do to maintain a comfortable temperature.
Check your boiler’s flow temperature. If you have a suitable condensing boiler, an unnecessarily high setting may reduce efficiency. Adjustments should be made carefully, and the correct approach depends on your heating and hot-water system.
Keep the boiler serviced. Regular servicing helps ensure the appliance is operating correctly and can identify developing problems.
Consider replacement if your boiler is old and inefficient. Replacing an older non-condensing boiler with a modern condensing model can reduce gas consumption, although the savings depend on the existing appliance, the new installation and how the heating is used.
Frequently asked questions
How much does it cost to run a 24kW gas boiler for one hour?
It depends on the boiler’s actual gas consumption. A 24kW useful heat output isn’t necessarily the same as 24kW of gas input. If a boiler consumed 24kWh of gas during an hour, it would cost £1.68 at an illustrative rate of 7p/kWh.
How much does it cost to run a 30kW boiler for eight hours?
You can’t calculate this accurately from the maximum output alone. The boiler may operate at a lower output or stop firing during those eight hours. Use actual gas consumption to estimate the cost.
Is it cheaper to leave the heating on all day?
Not necessarily. Keeping a home warm continuously can increase heat loss compared with allowing the temperature to fall when heating isn’t needed. The most economical approach depends on the property, heating system and occupancy, but suitable schedules generally help avoid unnecessary heating.
Does turning down the boiler temperature save gas?
Reducing an unnecessarily high central-heating flow temperature can improve the efficiency of a suitable condensing boiler. However, it needs to remain high enough to heat the home properly, and systems with hot-water cylinders require additional care.
How do I find out how much gas my boiler uses?
Check your smart-meter data or compare gas-meter readings over a representative period. Your supplier’s bill will show consumption in kWh, which you can multiply by your unit rate to calculate the cost.
Sources
GOV.UK, Gas meter readings and bill calculation – https://www.gov.uk/guidance/gas-meter-readings-and-bill-calculation
Ofgem, Understand your electricity and gas bills https://www.ofgem.gov.uk/understand-your-electricity-and-gas-bills
Accurate as of: 7 September 2026