Gas combi boilers are the most popular choice for central heating systems in the UK due to their energy efficiency and compact design. However, the cost of running a boiler can vary depending on factors such as the brand, model, power output and energy efficiency rating. One of the biggest indicators of cost is the power output which is determined by the size of your home and the number of bathrooms that need to be serviced by the heating system. So let's explain these costs.
What is a boiler energy rating?
The energy efficiency rating of a boiler indicates how well, from a cost perspective, the system converts energy into heat. The rating is measured using "ErP" or the Energy-related Products Directive, sometimes expressed as "ER", with the most energy efficient being rated at A+++ down to G, which is the least efficient. The majority of boilers on the market tend to have a rating of A or A+.
Get an instant price on a new combi boiler, starting at just £1,495.What does the power output mean?
Now we get a little bit technical, but once you understand the concept of kilowatt-hours (kWh) it's relatively easy to estimate the cost. The output of power is measured in kilowatts (kW) and the output needed depends on the size of your home. Here are some examples that are normally suitable for homes in the UK:
- 24-27 kW: 1-2 bedroom homes
- 28-24 kW: 3-4 bedroom homes
- 35-42 kW: 5+ bedroom homes
How does this convert into cost?
So let's keep it simple and use a 30 kW boiler as an example. This means the boiler needs to use 30 kilowatts, or 30,000 watts, of energy to operate. If the boiler is running at this rate for one hour this equates to 30 kWh, 30 kilowatt hours.
The average cost of gas in the UK in 2024 is 4.17 pence per kilowatt hour (kWh). Let's say it's 4p per kWh to make this easily calculable.
If we run a 1 kilowatt boiler for one hour would be cost 4 pence. The cost of one kilowatt for one hour (kWh).
Now running our 30 kW boiler for an hour would cost 120p or £1.20 (30 kilowatts for one hour, times 4p).
So now we could estimate that if we use our 30 kW boiler, at 4p per kWh, for three hours a day, that would be:
30 (kW) x 4 (pence) x 3 (hours) = £3.60 per day.
