Boilers are crucial for providing essential heating and hot water, and can significantly impact comfort, energy efficiency, and even property value. But exactly how much gas does a boiler use per hour, and how much is that costing you?

Knowing how much gas your boiler uses is essential for reducing energy expenses or comparing alternatives. The boiler is one of the most energy-intensive appliances in your home and a significant contributor to your energy bill.

According to Ofgem, Great Britain’s independent energy regulator, a typical household in England, Scotland, and Wales uses 11,500 kWh of gas annually, which is around 958 kWh per month. Your boiler is probably doing more heavy lifting than you think, depending on its size, efficiency, how long it runs, and how well your home retains heat.

Most people don’t realise just how quickly those kilowatt-hours add up, or how small changes, such as lowering the flow temperature or fixing a faulty thermostat, can make a noticeable difference in monthly bills. The last thing you want is to pay more than necessary for energy.

Understanding how much gas your boiler uses per hour isn’t just a technical curiosity; it’s key to controlling your costs without sacrificing warmth.

Quick Takeaways on How Much Gas Does A Boiler Use Per Hour:

• The amount of gas your boiler uses will depend on its size, how long you use it, and its efficiency.
• The costs included in your gas bill include the unit price rate, standing charges, and VAT.
• From 1 July to 30 September 2025, Ofgem set the price cap per gas unit to 6.33p per kWh, including VAT.
• The standing charge is 29.82p per day for gas, which adds up to about £9 per month until 30 September 2025.
• Your boiler may use too much gas due to a faulty thermostat or programmer, part failures, a pilot light, or an aging boiler.
• Keeping your boiler serviced and well-maintained can help reduce the gas it uses.

How Much Gas Does A Boiler Use?

Each household has different energy needs, so it’s challenging to provide a precise figure for how much gas your boiler should use.

Your boiler’s exact gas consumption will depend on several factors, including the amount of time you use it (in hours per day), its size (measured in kWh), its efficiency rating, and the boiler temperature settings you use.

However, you can use your boiler size to work out an estimate.

Boiler sizes in the UK are measured in kilowatts (kW) and range from 24 kW to around 40 kW.

An average 35 kWh gas boiler in the UK will consume 35 kilowatt-hours worth of gas.

Therefore, if your gas boiler runs for around 8 hours daily, it will use around 280 kWh of gas.

The above example is based on the UK average boiler size of 35 kWh. If your boiler is a different size, you can easily work it out by using the following formula:

Your boiler size (in kW) x the hours used per day = daily gas consumption (measured in kWh).

For example, if your boiler has a size (in power output) of 30 kW and you use it for 5 hours each day, you will use 150 kWh (30 x 5) of gas daily.

What Is A Kilowatt-Hour (kWh)?

To understand how much gas your boiler is using, it helps to know what a kilowatt-hour (kWh) actually means. It’s the standard unit of energy you’ll see on your gas and electricity bills, and it directly affects what you pay.

A kilowatt-hour is the amount of energy used by a 1,000-watt (or 1 kilowatt) appliance running for one hour.

So, if you have a 24 kW boiler running at full power for one hour, it would use:
24 × 1 = 24 kWh of gas.

At the current UK gas price cap of 6.33p per kWh (July to September 2025), that means:
24 × 6.33p = £1.52 to run your boiler for an hour at full output.

Of course, most boilers don’t run flat-out the whole time. They cycle on and off as needed, so your real usage (and cost) will usually be lower.

Knowing how kilowatt-hours work gives you a clear way to connect the dots between your boiler, your gas meter, and your monthly energy bill. It’s the key to understanding how small adjustments like reducing boiler output or shortening heating hours can add up to real savings.

What Costs Are Included In Your Energy Bill?

When you check your monthly gas bill, you’re not just paying for the energy you use. Several different charges are bundled into your final total, some based on usage, others on flat fees. Understanding what’s included can help you figure out how much of your bill is down to your boiler and how much is fixed, no matter how little gas you use.

Here’s a quick breakdown of the main components:

1. Unit Rate for Gas (per kWh)

This is the amount you’re charged for each kilowatt-hour of gas you use. As of July–September 2025, the unit rate for gas is 6.33p per kWh under the Ofgem price cap (for customers on standard variable tariffs paying by Direct Debit). This is the part of your bill directly affected by how long your boiler runs and how much energy it consumes.

2. Standing Charge for Gas

This is a fixed daily fee that covers the cost of maintaining the gas network and delivering gas to your home. You pay it whether you use 1 kWh or 100 kWh. From July–September 2025, the gas standing charge is 29.82p per day, which adds up to about £9 per month, even if your usage is low.

3. VAT

All domestic gas usage is subject to 5% VAT, which is automatically included in the prices quoted on most bills and on the Ofgem price cap.

4. Supplier Overheads

Energy suppliers also include their operating costs in your bill. Things like customer service, billing systems, and profit margins. These aren’t itemised separately, but they’re built into the unit rate.

Your exact figure will depend on factors like your supplier, where you live, how you pay, and the age of your boiler.

So What Can You Control?

Out of all these components, the one you have most control over is your usage. Lowering the number of kilowatt-hours your boiler consumes by adjusting flow temperatures, improving insulation, or reducing heating hours can make a real dent in your bill.

Even though the standing charge and VAT are fixed, using less gas means you pay less per month overall, especially in the colder seasons when boiler use spikes.

How Is Your Energy Bill Calculated?

Suppliers calculate your gas bill based on various criteria. These include:

• Your energy consumption: The more energy you use, the higher your bill.
• The tariff you’re on: This determines the price you pay for your daily standing charges and the cost of each unit of energy you use.
• Your bill payment method: Customers paying monthly by Direct Debit pay less than those using other payment methods.
• Where you live: Some areas of the UK pay more for their energy than others. This is because the cost of delivering energy to your home varies by region.

How Much Does It Cost to Run a Boiler Per Hour, Day, and Month?

Now that you know how energy bills are calculated, let’s break down exactly how much your gas boiler might be costing you—per hour, day, and month.

The key factors are:

• Boiler size (in kilowatts, or kW)
• Hours of use per day
• Unit rate for gas (currently 6.33p per kWh)
• Standing charge (currently 29.82p per day)

Here are some common examples:

Hourly Running Costs (Full Output)

Boiler Size	Gas Used per Hour	Cost per Hour (@ 6.33p/kWh)
18 kW	18 kWh	£1.14
24 kW	24 kWh	£1.52
30 kW	30 kWh	£1.90
35 kW	35 kWh	£2.22

These figures assume your boiler is running at full output. In reality, usage varies with room temperature, thermostat settings, and how well insulated your home is.

Daily Running Costs (5 Hours per Day)

Boiler Size	Daily Usage (kWh)	Cost (@ 6.33p/kWh)	+ Standing Charge	Total Daily Cost
18 kW	90 kWh	£5.70	£0.30	£6.00
24 kW	120 kWh	£7.60	£0.30	£7.90
30 kW	150 kWh	£9.50	£0.30	£9.80
35 kW	175 kWh	£11.08	£0.30	£11.38

Monthly Running Costs (Heating Daily)

Boiler Size	Monthly Usage (kWh)	Cost per Month (@ 6.33p/kWh)	Standing Charge (30 days)	Total Monthly Cost
18 kW	2,700 kWh	£170.91	£8.95	£179.86
24 kW	3,600 kWh	£227.88	£8.95	£236.83
30 kW	4,500 kWh	£284.85	£8.95	£293.80
35 kW	5,250 kWh	£332.33	£8.95	£341.28

How Much Gas Does The Average Home Use?

The amount of gas you use will vary depending on your home type and the number of residents in your household.

A larger home means more rooms or space to heat, and more people mean more hot water and higher gas usage.

The table below shows Ofgem’s estimates of average energy usage by house size. Ofgem uses these figures to calculate the energy price cap.

Energy Usage	Home Type	Number of Residents	Annual Gas Use (kWh)
Low	Flat or 1-bedroom house	1 to 2 people	7,500
Medium	2–3 bedroom house	2 to 3 people	11,500
High	4+ bedroom house	4 to 5 people	17,000

Is Your Boiler Using Too Much Gas?

If you suspect your boiler is using too much gas, the first step is to verify your usage and compare it to your gas bill.

Checking your gas usage against your bill will help you determine if your energy supplier has undercharged or overcharged you.

Even if there are no irregularities in your energy bill, it’s still a good idea to regularly check your energy usage so that you can keep tabs on it and moderate your behaviour as much as possible.

This can help you reduce energy use and save money on your heating bills.

Check out our video on how to vet boiler brands/models in the UK:

Why Is My Boiler Using Too Much Gas?

If your heating bill has gone up and your usage seems off, your boiler might be burning more gas than it needs to. Let’s look at the most common reasons why.

1. Your Boiler Might Be Too Powerful for Your Home

If your boiler is oversized, it could be the reason your gas usage feels excessive. Bigger boilers are designed for larger homes with more rooms, but when installed in smaller properties, they often cycle on and off rapidly.

This on/off behaviour, called “short cycling,” wastes energy and puts extra strain on the system. Instead of steady, efficient heating, the boiler constantly revs up and shuts down, using more gas than necessary.

Many UK homes only need a 24–30 kW boiler, but older installations may use 35 kW or more. If you suspect your boiler is too powerful for your needs, it’s worth speaking to a heating engineer who can assess your home and recommend the right output.

2. Your Boiler Flow Temperature Is Set Too High

One of the easiest ways to lower your boiler’s gas usage is to reduce the flow temperature. Many boilers in the UK are set to run at 70–80°C by default, but that’s often more than you need.

When a boiler runs hotter than necessary, it becomes less efficient, especially in condensing models, which are designed to recover heat from exhaust gases at lower flow temperatures. Running too hot bypasses this feature and burns more gas.

Lowering the flow temperature to 55–60°C won’t make your home cold, but it will allow your boiler to condense more effectively. This can improve efficiency by up to 6–8%, especially in newer models. It’s a small change that makes a noticeable difference.

3. Your Home Is Losing Heat Too Quickly

Even the most efficient boiler can’t save you money if your home is leaking heat. Poor insulation means your boiler has to work harder and run for longer just to maintain the same temperature. This leads to higher energy bills and more carbon emissions.

Common culprits include uninsulated lofts, single-glazed windows, draughty doors, and thin walls. If the heat you’re paying for escapes as quickly as it’s generated, your gas usage will naturally spike. According to the Energy Saving Trust, a typical uninsulated home loses about 25% of heat through the roof, 33% through the walls, and 10-20% through the floor.

Adding loft insulation, sealing gaps, using thermal curtains, and upgrading to double glazing can make a significant difference. These improvements reduce how often your boiler kicks in and how long it stays on, helping you cut gas usage without compromising on warmth.

4. You Might Have a Faulty Thermostat or Controls

Old or inaccurate thermostats can cause your boiler to run when it doesn’t need to or stay on for longer than necessary. If your thermostat is misreading room temperature, it might signal your boiler to fire up even when your home is already warm.

Similarly, outdated timers and manual controls may not reflect your daily routine, keeping the heating on when you’re asleep or away. This leads to wasted gas and higher bills. Upgrading to a smart or programmable thermostat can help fix this.

These devices learn your schedule and adjust heating times accordingly. Some even track weather patterns and occupancy, optimising boiler usage for comfort and efficiency. A simple upgrade can make a big dent in energy waste.

5. There May Be Sludge or Blockages in the System

Over time, heating systems can collect a build-up of sludge, usually a mix of rust, scale, and other debris. This gunk settles in radiators and pipes, making it harder for hot water to circulate. The result? Your radiators feel lukewarm, and your boiler has to work much harder (and longer) to reach your set temperature.

More gas gets burned just to achieve the same result. Sludge can also increase wear and tear, potentially leading to breakdowns. A qualified engineer can flush the system to clear out debris and add inhibitors to prevent future build-up.

If your heating is uneven or slow to warm, sludge could be to blame, and it’s costing you more than you think.

6. The Pilot Light Is Burning Constantly (Older Boilers)

If you have an older boiler with a permanent pilot light, that tiny blue flame could be burning through more gas than you realise. Traditional boilers keep the pilot light on 24/7 to ignite the burner when needed.

While it may seem insignificant, a constantly lit pilot can use up to 1.5 kWh of gas per day, which adds up over time. That’s around £2.85 per month to keep the flame going, even when you don’t need heat or hot water.

Modern condensing boilers use electronic ignition instead, which only triggers the flame when required. If your boiler still uses a standing pilot light, it might be time to consider upgrading to a newer, more energy-efficient model.

7. Worn or Failing Parts Are Affecting Efficiency

Boilers rely on multiple internal components, like the fan, gas valve, thermocouple, and heat exchanger, to operate efficiently. When one of these parts starts to wear out or fail, the boiler may run longer than necessary, burn more gas, or cycle inconsistently.

For example, a faulty heat exchanger might struggle to transfer heat properly, forcing the system to stay on longer to achieve the same warmth. Likewise, a misfiring ignition or a sticking valve can lead to short cycling or extended burner operation.

These issues aren’t always obvious day to day, but they can quietly increase your gas usage and bills. If your boiler has become noisier, slower to heat, or less responsive, a service call could reveal hidden inefficiencies.

8. The Boiler Itself May Be Outdated or Inefficient

Older boilers tend to burn more gas for the same amount of heat. Non-condensing boilers, especially those over 15 years old, often operate at just 60–75% efficiency, meaning a quarter or more of the gas you pay for is wasted.

Modern condensing boilers, by contrast, can reach efficiencies of 90% or more. They reuse waste heat from flue gases, making them far more economical. Even if your old boiler still works, it may be quietly driving up your energy bills every month.

If your boiler is aging, noisy, or frequently needs repairs, it could be time to consider an upgrade. Replacing it with an A-rated model can significantly reduce long-term gas usage and running costs.

Have you heard about the gas boiler ban and are wondering what the alternatives to gas boilers are? Check out our complete guide to replacing your gas boiler with a heat pump.

How Boiler Efficiency Ratings Work

Not all boilers use gas the same way. Efficiency ratings help you understand how well your boiler converts gas into usable heat and how much of it goes to waste. The higher the efficiency, the less gas your boiler needs to keep your home warm.

Boiler efficiency is measured as a percentage. An efficiency of 90% means 90% of the gas burned is turned into heat, while 10% is lost through the flue (usually as hot air or exhaust gases).

Here’s how common boiler ratings compare:

Boiler Type	Efficiency Rating	Typical Fuel Waste
A-rated (modern condensing)	90–94%	6–10%
B to C-rated (older condensing)	80–89%	11–20%
D to G-rated (non-condensing)	60–79%	21–40%+

What Makes a Boiler More Efficient?

Modern condensing boilers are now standard across the UK and are much more efficient because they recover heat from the exhaust gases before they escape through the flue. Older non-condensing models waste that heat entirely.

Other factors that affect a boiler’s efficiency:

• Age: Efficiency drops over time, even in good models.
• Maintenance: Sludge, soot, or faulty parts reduce performance.
• Installation quality: A high-rated boiler poorly installed can still waste gas.
• Flow temperature: Condensing boilers only reach peak efficiency when flow temperatures are lower (typically 55–60°C).

If your boiler has a visible efficiency label or EPC rating, check it. Anything rated below 86% could be costing you far more to run.

How Can You Reduce the Amount of Gas Your Boiler Uses?

Cutting your gas bill doesn’t have to mean sitting in a cold house. You may be using more energy than you need simply because your heating system isn’t set up efficiently. A few smart adjustments can make your home more comfortable and affordable to heat, especially during winter.

Here are the most effective ways to reduce boiler gas usage without losing warmth:

1. Install Thermostatic Radiator Valves (TRVs)

TRVs let you control the temperature of individual radiators, so you’re not heating empty rooms to the same level as your living space. Lowering unused bedrooms or hallways to a cooler setting reduces total gas use without affecting comfort in the rooms you spend time in.

2. Use Zoned Heating Where Possible

If your heating system supports it, split your home into zones—for example, upstairs and downstairs. Zoned heating allows you to heat only certain parts of the house at different times of day, reducing boiler runtime and avoiding heating rooms that don’t need it.

3. Turn Down Room Thermostats Slightly

Lowering your room thermostat by just 1°C can reduce your heating bill by up to 10% per year. Most people don’t notice the difference between 21°C and 20°C, but your gas meter certainly will.

4. Bleed Radiators and Balance the System

Cold spots in radiators mean poor circulation, forcing the boiler to work harder. Bleeding your radiators removes trapped air, while balancing ensures all rooms heat evenly. This helps your boiler heat the home more effectively, without burning extra fuel.

5. Reduce Heat-Up Time With a Boiler Warm-Up Cycle

Many modern boilers include an ‘eco’ or ‘preheat’ setting that keeps hot water ready to go at all times, but this comes at an energy cost. Disabling the preheat function (especially overnight or when you’re away) prevents the boiler from firing unnecessarily to maintain standby warmth.

6. Close Curtains at Sunset, Open Them During the Day

Letting natural sunlight warm your rooms during the day means your boiler does less work. In the evening, closing curtains traps heat indoors. This simple habit helps stabilise indoor temperatures and reduces how often the boiler needs to switch on to top things up.

7. Schedule an Annual Boiler Service

A yearly service helps catch minor problems like inefficient burners, worn valves, or leaks before they become expensive. A well-maintained boiler runs more smoothly, uses less gas, and is far less likely to break down when you need it most.

Summary on How Much Gas Does A Boiler Use

Keeping an eye on how much gas your boiler uses can help you keep energy costs to a minimum while reducing your carbon footprint. An efficient boiler ensures you don’t use more gas than needed and keeps your energy bills reasonable.

Always stay informed about price changes and look for lower tariffs from different suppliers. Small changes like lowering the flow temperature can lead to noticeable savings without sacrificing warmth or comfort.

Ensure you have your boiler serviced by a qualified heating engineer to identify and prevent any issues that can cause it to use more gas than necessary. Most importantly, if you’re using an old, inefficient boiler, consider replacing it with a modern, A-rated model that will waste less gas when providing your home with heating or hot water.

How old is your boiler? Should you consider repairing your boiler or start looking at the latest boiler prices? It’s no secret that boiler efficiency deteriorates over time.

FAQs on How Much Gas Does A Boiler Use

How Much Gas Does a Boiler Use in the UK?

The amount of gas a boiler uses in the UK depends on its size, efficiency, and how long it runs each day. On average, a typical UK household uses between 30 and 90 kWh of gas per day for heating during colder months. For example, a 30 kW boiler running for 3 hours would use around 90 kWh. Usage tends to be lower in smaller or well-insulated homes, and higher in larger or poorly insulated ones.

How Much Energy Does a Boiler Use Per Hour?

A boiler’s hourly energy use is measured in kilowatt-hours (kWh) and is equal to its output rating. So a 24 kW boiler running at full capacity for one hour uses 24 kWh of energy. However, most boilers don’t run at full output all the time. They cycle based on room temperature and heating demand, so actual hourly usage is often lower.

How Much Gas Does a 35 kW Boiler Use?

A 35 kW boiler running at full capacity uses 35 kWh of gas per hour. At the current UK unit rate of 6.33p per kWh, that equates to £2.22 per hour. If the boiler runs for 5 hours a day, that’s 175 kWh daily, or approximately £11.08, plus the standing charge.

How Many Hours Should My Boiler Run Per Day?

It depends on your home size, insulation, and outside temperature. Most UK households run their boiler between 4 and 8 hours per day in winter, often split between morning and evening heating periods. Well-insulated homes may need less. Smart thermostats and zoning can help optimise runtime while maintaining comfort.

How to Calculate Gas Consumption of a Boiler?

To calculate how much gas your boiler uses, multiply the boiler’s size in kilowatts (kW) by the number of hours it runs. This gives you the total energy used in kilowatt-hours (kWh).

Formula:
Boiler Size (kW) × Hours Used = Total kWh

Then, multiply that figure by the gas unit rate (currently 6.33p per kWh, as of July–September 2025). Add the daily standing charge (29.82p) to get the full daily cost.

For example, if you have a 30 kW boiler that runs for 5 hours per day:

• 30 × 5 = 150 kWh
• 150 × 6.33p = £9.50
• Add standing charge: £9.50 + £0.30 ≈ £9.80 total per day

Sources and References

Ofgem – Average gas and electricity usage

Ofgem – Energy price cap

Energy Saving Trust – Home insulation to reduce home heat loss