Homeowners Professionals

How much gas does a boiler use per hour?

Not everyone pays attention to how much gas and electricity they use in a month. However, it’s always worth checking your usage against your bill to make sure you haven’t been over- or under-charged by your energy supplier. It’s also good to be aware of the energy you’re using so you can make a conscious effort to try to reduce your usage to benefit both the environment and your bank balance.

How much gas your boiler consumes will depend on its size, efficiency and how many hours it’s in use per day. Boiler sizes are measured in kilowatts (kW) and range from 24-27 kW, 28-34 kW and 35-42 kW. A house with one bathroom and 10 radiators would need a 24-27 kW boiler, whereas a large house with over 20 radiators and three bathrooms or more would need a 35-42 kW boiler.


A kilowatt hour (kWh) is a unit of energy that demonstrates how much energy an appliance could use if it was on for one hour. A one kW hair dryer would use one kWh of energy if it was on for 60 minutes, for example.

Using kW and kWh, you can work out how much gas your boiler is using and therefore how much it costs. A 24 kW boiler will use 24 kWh of energy per hour. According to  Choose, the cost is approximately 3.8 pence per kWh, which means it would cost around 91 pence to run a 24 kW boiler for one hour. This will change depending on the cost of gas and the size and age of your boiler.

According to  Ofgem, the average gas consumption of a UK household was between 8,000 kWh and 17,000 kWh in 2017, which is an average cost of £1,123 for both gas and electricity. Ofgem calculates this to be broken down to £487 per year for electricity and £636 per year for natural gas*. To find out exactly how much gas your boiler is using, you could ask your supplier to fit a smart meter. Many companies will do this at no additional cost and it allows you to track your usage in real time.

If you’re looking to switch energy suppliers, there’s an easy calculation you can do to determine the overall yearly cost. You should take your annual gas usage (for example, 13,537 kWh) and multiple this by the Tariff Comparison Rate (TCR). The TCR is a rate that allows you to compare one tariff against another. For example, if you were to pay four pence per KWh, the calculation could look something like:

13,537 kWh x 0.04 p/kWh (TCR) = £541.48 estimated cost per year

The 2022 energy price cap changes

*Please note that energy prices can change and the costs above are based on longer term averages. Changes to the price cap in April 2022  mean homeowners are now paying more per KWh for both electricity and gas. Rates as of April 2022 are on average  26 pence per kWh for electric and 7 pence per kWh for gas. You can find out your rate on your lastest statement from your energy supplier.

  • At 7 pence per kWh for gas your 24kW boiler would cost you £1.68 per hour to run 
  • If your boiler runs for an average of 5 hours per day this will cost you £8.40 per day



How much gas should my boiler use?

It’s hard to give a precise figure to say how much gas your boiler should be using, however you can use the size of your boiler to work out an estimate. A 24 kW boiler will use 24 kW of energy per hour. If your boiler is on for a total of five hours per day, your daily usage should be around 120 kWh.

But if you’ve noticed an increase in your gas bill recently, your boiler could be using more gas than it should. First, you should check with your supplier that they haven’t increased the prices. Remember that newer contracts could include a daily standing charge that should be paid irrespective of the amount of gas you’re using.

You should also look at your statement to see how many kWh it says you’ve used. Don’t forget you’ll use much more gas in winter than in summer. If you don’t think this is the reason for your high gas bill, here are some other reasons you may be overpaying.

A broken thermostat or programmer

Thermostats and/or programmers automatically control your boiler so you don’t have to oversee it manually. These functions will turn the boiler on or off at times that you have predetermined or they will turn the boiler off when the house reaches a set temperature.

A faulty thermostat and/or programmer could result in your boiler staying on for 24 hours a day, which could become very expensive. You can do a couple of quick checks yourself, such as making sure these functions are set to the correct times and/or temperatures, and that they are on.

If the above are all as they should be, you should call a heating engineer to check the thermostat and/or programmer and replace them if they’re no longer working correctly.

Most modern boilers come with smart controls that allow you to control your heating and hot water system from your mobile phone via an app. Smart controls could be more reliable than a thermostat and/or programmer and may improve efficiency.

A faulty motorised valve

A motorised valve is what controls the flow of hot water from the boiler into a cylinder or to the radiators. When the boiler is on, the valve opens to allow the water to flow and then it closes again to stop the water.

The valve could become stuck or could fail altogether. This means your radiators might be heating up when you don’t want them to.

Your pilot light could also be using gas. Read on to find out more about this problem.  

Does an old boiler use more gas?

About 60 per cent of your total energy bill for the year is down to your boiler, so upgrading to a more efficient model could save you some money.

Most  new gas boilers  could be up to 95 per cent efficient but boilers that are over 10 years old could see up to a 30 per cent drop.

Boilers have an efficiency system that provides them with a rating. There are a couple of rating systems that are currently in use in the UK. The newest system is ErP. The  ErP system  gives each boiler a letter rating from A-G, with A being the most efficient (90 per cent or higher). The SEDBUK rating can be found on systems that were installed prior to 2015 and provides each individual boiler with an efficiency percentage. If you’re getting a new boiler, it is advised that you pay attention to its efficiency rating.

How much gas does a boiler pilot light use?

A pilot light is a small flame that burns constantly. It remains lit because it is used to ignite the main burner when the boiler needs to be turned on. As they burn all day and night, they are always using a small amount of gas. According to  Energuide, your pilot light could be costing you up to £82 per year.

Boilers that are 15 years old or younger don’t have pilot lights. Instead, they’re fitted with an electronic ignition. If your boiler has a pilot, it could be worth looking at an energy-efficient replacement. This could save you on the gas that’s been used for your pilot light and your new boiler would be much more energy efficient.

Ensuring your boiler is efficient is important if you want to keep your gas bills at a reasonable level and not use more gas than you need to. If you look after your gas boiler by maintaining it well and getting it serviced each year, it could stay more efficient for longer.  

Time to upgrade your heating?
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