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Enter your boiler kW rating, daily usage hours, and efficiency to instantly calculate your gas central heating running costs using the current Ofgem rate of 6.24p/kWh for 2026.
Quick select boiler type:
A-rated condensing boilers: 90-94% | Older non-condensing: 70-80%
Daily Cost
£13.31
Weekly Cost
£93.18
Cost for 30 Days
£399.36
Annual Estimate
£4858.88
Important: Please rely on a professional, accredited Gas Safe engineer and accredited tools for all measuring. This calculator provides estimates only and accepts no liability for calculations.
The cost of running a gas boiler depends on its kW rating, how many hours it runs per day, the gas unit rate, and the boiler’s efficiency. At the current Ofgem rate of 6.24p/kWh, a typical 24kW combi boiler running 8 hours per day at 90% efficiency costs around £13.32 per day or £399.47 per month.
It is important to note that boilers do not run at full rate continuously. Modern condensing boilers modulate their output, adjusting the flame size to match the heat demand. A 24kW combi boiler heating a typical 3-bedroom semi-detached home might average just 10-15kW of actual consumption over the course of a day, as the boiler cycles on and off and reduces its output once the target temperature is reached.
The calculator above uses the full kW rating for a worst-case estimate. For a more realistic figure, try entering 50-65% of your boiler’s rated kW to account for modulation.
The table below shows estimated gas central heating running costs for common boiler sizes at 8 hours per day, 30 days, 90% efficiency, and the current 6.24p/kWh rate:
| Boiler Size | Daily Cost | Weekly Cost | Monthly Cost (30 days) |
|---|---|---|---|
| 24kW Combi | £13.31 | £93.18 | £399.36 |
| 28kW Combi | £15.53 | £108.71 | £465.92 |
| 30kW Combi | £16.64 | £116.48 | £499.20 |
| 35kW System | £19.41 | £135.89 | £582.40 |
These figures assume the boiler runs at full rated output for 8 hours per day. Real-world costs are typically 30-50% lower due to modulation and thermostatic control.
Boiler efficiency measures how effectively your boiler converts gas into usable heat. The higher the efficiency percentage, the less gas is wasted and the lower your gas heating costs. Efficiency is the single biggest factor in determining your gas boiler running costs.
90-94%
Modern condensing boilers recover heat from exhaust gases that older boilers waste. They are the minimum standard for new installations in the UK since 2005 and deliver the lowest running costs.
70-80%
Non-condensing boilers let hot exhaust gases escape without recovering heat. If your boiler was installed before 2005, it is likely non-condensing and costing you significantly more to run.
A boiler rated at 90% efficiency means that for every pound of gas you pay for, 90p goes towards heating your home and 10p is lost as waste heat. A boiler at 75% efficiency wastes 25p of every pound — that adds up to hundreds of pounds over a year.
Example: A 90% efficient 24kW boiler uses 26.67 kWh of gas to deliver 24kW of heat.
A 75% efficient 24kW boiler uses 32.00 kWh of gas to deliver the same 24kW of heat.
That is 5.33 kWh more gas every hour — an extra £2.66 per day at 8 hours of use.
The type of boiler you have affects both your gas central heating running costs and the way your heating system operates. Here is how the three main types compare:
24-40kW typical
Running cost: Heats water only when needed, so no energy is wasted keeping a cylinder hot. Most cost-effective for 1-2 bathroom homes.
12-30kW typical
Running cost: Slightly higher than combi due to cylinder heat losses, but lower kW rating means less gas per hour of heating.
12-30kW typical
Running cost: Highest of the three types due to cylinder and header tank heat losses, plus older systems often have lower efficiency ratings.
Even small changes can make a noticeable difference to your gas central heating running costs. Here are the most effective ways to cut your gas bills:
A yearly service by a Gas Safe registered engineer keeps your boiler running at peak efficiency. A neglected boiler can lose 5-10% efficiency over time due to dirty heat exchangers, worn seals, and incorrect gas pressure. Servicing typically costs £60-£100 and can save far more over the year in reduced gas consumption.
Trapped air in radiators prevents them from heating fully, meaning your boiler has to work harder and run longer to reach the set temperature. Bleeding radiators is a simple DIY task — if the top of your radiators feels cold while the bottom is warm, they need bleeding.
Smart thermostats like Nest, Hive, or Tado learn your schedule and adjust heating automatically. They can reduce your gas usage by 10-15% by avoiding unnecessary heating when you are out or asleep. Many also allow remote control via your phone, so you never heat an empty house.
Poor insulation is the biggest cause of wasted heating energy. Loft insulation (£300-£400) can save around £150 per year, and cavity wall insulation (£400-£600) can save a further £150-£200. Draught-proofing doors and windows is an inexpensive way to stop warm air escaping and reduce how long your boiler needs to run each day.
If your boiler is over 15 years old, it is likely running at 70-80% efficiency. Replacing it with a modern A-rated condensing boiler at 90%+ efficiency could save you £200-£300 per year on gas bills. With a typical installation cost of £1,500-£3,000, the investment pays for itself within 5-10 years, and you benefit from improved reliability and a new warranty.