Gas is easy to work out, because in most homes almost all of it goes through a single appliance. The boiler heats your radiators and your hot water, and between them those two jobs account for the overwhelming share of the gas you pay for. A gas hob or oven adds a little on top, and that is roughly the whole list. So when a gas bill looks high, the question is really which of those two jobs is eating the units, because that tells you exactly where a saving will come from. This guide breaks the bill down by end use, shows how to read your own split off the meter, and points you at the slice worth attacking first.
The short answer. Space heating is the biggest user of gas by a wide margin, typically around 60 to 70 per cent of a home's gas over a year. Hot water is next, usually 20 to 30 per cent, and it is the reason your gas bill never falls to nothing in summer. Gas cooking, where you have it, is a small slice, often only a few per cent. So the boiler and how it heats the house is where nearly all the money is, and where nearly all the savings are.
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The boiler is almost the whole story
If your home runs on mains gas, look at what is actually connected to the supply. It is the boiler, and perhaps a hob or oven. That is a very different picture from electricity, where the load is spread across dozens of appliances, from the fridge to the telly to the kettle, as the companion guide on what uses the most electricity sets out. Gas has no such spread. One appliance does the heavy lifting, which is good news, because it means you only have one thing to get right. Bring the boiler's gas use down and the whole bill follows. On top of the units the boiler burns sits the daily gas standing charge, a fixed sum of roughly 29p a day that you pay whether the boiler fires or not, so it never changes when you cut back.
Space heating: the biggest slice by a distance
Warming the house is where most of the gas goes, and it is not close. Every degree you hold a room above the temperature outside is heat leaking through the walls, roof, windows and gaps, and the boiler has to keep replacing it for as long as the heating is on. Over a cold British winter that adds up to thousands of kilowatt hours. In a typical three-bed home the heating alone might account for something like 8,000 kWh of gas a year out of a total near 11,000 to 12,000, which at an example rate of 7.3p per kWh is roughly £580 of the bill. The exact figure swings with how warm you keep the place, how many hours the heating runs and how well the building holds heat, but the ranking rarely changes: heating is the top line every time. The cost of heating a house works through the season-long numbers by home size.
Two things make the heating slice bigger than it needs to be. The first is a boiler set to send very hot water to the radiators, which knocks it out of its efficient condensing mode and wastes gas for no extra warmth. The second is a leaky building, because heat you have paid to make goes straight out through an uninsulated loft or an unsealed door. Both are fixable, and both are covered below.
Hot water: the floor under your summer bill
The second big user is hot water, and it explains a puzzle a lot of people notice: why the gas bill does not drop to zero once the heating goes off for the summer. That residue is your hot water. Heating water takes a surprising amount of energy, because water holds heat well, so every bath, shower and hot tap draws on the boiler even in July. Across a year hot water often comes to something like 2,000 to 3,000 kWh of gas, or roughly £150 to £220 at an example 7.3p per kWh, and in a household with several long daily showers it runs higher. It is a steady load rather than a seasonal one, which is why trimming it pays back all year rather than only in winter. The hot water savings guide has the full set of levers.
Gas cooking: smaller than the flame suggests
A gas hob throws out an impressive amount of heat, so people assume it costs a lot to run. It does not, in the scheme of a gas bill. Cooking is intermittent and brief compared with heating a whole house for hours, so even daily use of a gas hob and oven usually comes to only a few per cent of the total gas. As a rough sense of scale, a gas hob ring on a medium flame draws in the order of 1 to 2 kW, so twenty minutes of cooking might use around 0.5 kWh of gas, a handful of pence. Useful to know if you are weighing a gas hob against an electric or induction one, which the induction versus gas hob comparison covers, but not the place to look if your gas bill has jumped. When the total climbs, it is almost always heating or hot water behind it, not the cooker.
| What the gas does | Typical share of gas | Rough yearly use, three-bed home |
|---|---|---|
| Space heating (radiators) | ~60 to 70% | ~8,000 kWh |
| Hot water | ~20 to 30% | ~2,500 kWh |
| Cooking (if on gas) | a few % | ~300 kWh |
Illustrative shares for a typical gas-heated home. Yours will vary with how warm you keep the house, how much hot water you draw and whether you cook on gas. Homes without gas cooking simply split between heating and hot water.
How to see your own gas split
You do not have to guess, because your meter and the calendar tell you most of it. The clean trick is to compare summer with winter. In the warmest months, with the heating off, whatever gas the meter still counts is going on hot water and cooking, so a summer month's use is a fair reading of your non-heating gas. Take that figure, multiply it up across the year, and the rest of your annual gas is space heating. For a sharper look at any single job, read the meter before and after: note it first thing, run only the hot water for the day, or run a heating warm-up hour, and read again. A metric meter counts cubic metres, so multiply the difference by about 11.2 to get kilowatt hours, then by your unit rate for the cost. A smart meter in-home display shortcuts all of this by showing gas spend in pounds as it happens; watch it during a heating warm-up and again while a shower runs, and the split becomes obvious. To turn any usage figure into a running cost quickly, the running cost calculator does the arithmetic. For the whole-boiler picture, see how much a gas boiler costs to run.
Cutting the biggest slice first
Because heating is the top line, that is where the effort belongs. A few moves do most of the work.
- Turn the boiler flow temperature down. Many combi boilers leave the factory sending water to the radiators at 70C or more, which stops them condensing efficiently. Setting the flow temperature to around 55C to 60C can cut heating gas by roughly 8 to 12 per cent at no cost, as the boiler flow temperature guide explains.
- Heat only when you are home, and a degree lower. Every hour the heating runs is heat you pay to replace, so matching the timer to your actual routine and nudging the thermostat down a degree both shave the heating slice.
- Stop the heat escaping. A warm home that leaks heat just makes the boiler work harder. Loft insulation and draught-proofing are among the cheapest ways to lower the demand the boiler has to meet, so it fires less for the same warmth.
- Trim the hot water too. Shorter showers, a well-lagged cylinder and a sensible cylinder temperature all cut the year-round hot water load. A cylinder jacket is a few pounds and keeps stored water warm for longer.
The bottom line
In a home with gas, the money is not scattered about. Space heating takes the lion's share, hot water comes next and props up the summer bill, and cooking barely registers. That makes a high gas bill easy to diagnose: it is nearly always the heating, occasionally the hot water, and almost never the hob. So put your effort where the units are. Get the boiler condensing with a lower flow temperature, run the heating only when you need it, insulate so the house holds what it makes, and keep the hot water sensible. Do those and you have addressed the parts of the bill that actually cost you.
Common questions
What uses the most gas in a house?
Space heating, by a wide margin. Warming the radiators typically accounts for around 60 to 70 per cent of a home's gas over a year. Hot water is second at roughly 20 to 30 per cent, and gas cooking, where fitted, is usually only a few per cent.
Why is my gas bill high even in summer?
Because your hot water still runs on gas even when the heating is off. Water heating uses something like 2,000 to 3,000 kWh of gas a year, so a summer gas bill covers hot water plus the daily standing charge, even with the radiators cold.
Does a gas hob use a lot of gas?
No, not compared with heating the house. Cooking is brief and intermittent, so even daily use of a gas hob and oven usually comes to only a few per cent of a home's total gas. A ring on a medium flame uses roughly a few pence worth of gas in twenty minutes.
How can I work out my own gas breakdown?
Compare summer and winter meter readings. With the heating off in summer, whatever gas the meter counts is hot water and cooking, so that gives your non-heating use; the rest of the year's gas is space heating. A smart meter in-home display shows the split in pounds as you use it.