What would a new boiler save you?
An estimate of the gas a more efficient boiler would stop wasting, using your own unit rate. If the honest answer is that it would not save you much, the calculator says so.
- ✓Uses the rate off your own bill, not a national average
- ✓Shows the efficiency gap that drives the saving
- ✓Gives payback in years against a typical installation
- ✓Tells you to keep a good boiler when that is the answer
What would a new boiler save you?
An estimate of the gas a more efficient boiler would stop wasting. If the answer is "not much", it will say that.
When was your boiler fitted?
Your home
Your gas tariffBoth figures are on your bill.
Answer the first two and your estimate appears here.
Where the saving actually comes from
Efficiency is the share of the gas you buy that ends up as heat indoors rather than leaving through the flue. An old non-condensing boiler turns roughly seventy per cent of it into useful heat. A modern condensing boiler recovers heat from its own exhaust gases and manages around ninety. That missing thirty per cent is gas you paid for and never felt.
The sum behind the calculator follows from that. Your home needs a certain amount of heat each year regardless of what produces it, so a boiler that wastes less gas delivers the same warmth for less. The saving is the difference between what your current efficiency costs you and what ninety per cent would, priced at your own unit rate.
Which is also why the answer collapses for newer boilers. Going from eighty-nine per cent to ninety saves close to nothing, and any tool that tells you otherwise is selling something.
Ways to cut the bill without buying anything
If the calculator has told you a replacement will not pay for itself, these are the things that will actually move your bill, and none of them involve an installation.
Turn the flow temperature down
Most combis leave the factory set higher than they need to be. Dropping the heating flow to around 60C lets the boiler condense properly, which is where its efficiency comes from. Costs nothing.
Book the annual service
A serviced boiler runs closer to its rated efficiency, lasts longer, and keeps whatever warranty it still has intact. It is the cheapest thing on this list by a distance.
Bleed and balance the radiators
Air in the system means cold patches, and unbalanced radiators mean the far end of the house never keeps up while the near end cooks.
Use the controls properly
A room thermostat and thermostatic radiator valves, set to heat rooms when they are used and not when they are empty, save more in most homes than a percentage point of boiler efficiency.
What this estimate cannot see
It uses a typical annual gas figure for your size of home, so a household that is out all day, or one that keeps the heating on constantly, will sit either side of it. It assumes the new boiler achieves ninety per cent in service, which depends on how the system is set up rather than on the boiler alone. And it says nothing about insulation, which for many homes is the larger opportunity.
If the answer points towards replacing, our size calculator will tell you what output to ask for, and repair or replace is the better tool if yours has just failed. Our guide to boiler running costs covers the same ground in more detail.
Frequently asked questions
How much can a new boiler save on gas bills?
It depends almost entirely on what you have now. Replacing a pre-2005 non-condensing boiler in an average three bedroom house typically cuts gas use by around twenty per cent, which is meaningful money every year. Replacing a condensing boiler fitted in the last ten years saves very little, because the efficiency gap is only a few percentage points. The older the boiler, the bigger the prize.
Is it worth replacing a working boiler to save money?
Usually not on the savings alone. Even a good saving takes years to cover the cost of an installation, so a boiler that is working and is under about ten years old is generally better serviced than replaced. The calculation changes when the boiler is also unreliable, when a large repair bill has landed, or when it is old enough that the efficiency gap is wide.
What is boiler efficiency and why does it matter?
Efficiency is the share of the gas you buy that ends up as heat in your home rather than going out of the flue. A non-condensing boiler might turn seventy per cent of it into useful heat; a modern condensing one recovers heat from its own exhaust gases and manages around ninety. The other thirty per cent in the first case is gas you paid for and never felt.
Where do I find my gas unit rate?
On your gas bill or in your online account, quoted in pence per kilowatt hour, usually alongside a separate daily standing charge. Use the unit rate rather than the standing charge, because a new boiler changes how much gas you burn and not what you pay each day for the connection.
Will a new boiler cut my bills as much as the badge suggests?
Often slightly less. The efficiency figures on a new boiler assume it is condensing, which needs the water coming back from the radiators to be below roughly 55C. Systems with older radiators sized for hotter flow temperatures frequently run above that and lose part of the benefit. Ask the installer about turning the flow temperature down, which costs nothing and recovers most of the gap.
Does a new boiler cut carbon emissions?
Yes, in proportion to the gas it stops wasting, because burning less gas emits less carbon. It is worth being clear about the scale though: replacing an old gas boiler with a new gas boiler is an efficiency improvement rather than a switch away from fossil fuels. A heat pump is the larger step, and a very different job.