Do I need a new gas meter for a new boiler?

For most houses the answer is no. A standard domestic meter has enough capacity for a modern combi and the usual collection of gas appliances around it, and a straight boiler swap does not go near the limit.

It is still worth understanding, because the meter is the one part of a boiler installation that your installer cannot touch. If it turns out to be the constraint, the job does not get solved by a better fitter or a longer day. It gets solved by two other organisations working to their own timetables, and that is a diary problem rather than a plumbing one.

Why the meter comes up at all

Gas pipework is sized by calculation, not by habit, and the calculation starts at the meter outlet. An engineer works out the total gas rate of everything connected, follows the route to the appliance, and checks that the pressure drop across the whole installation stays inside the allowance. If the answer does not work, the first fix is a bigger pipe.

The meter is simply the next question up that chain. The pipe from the meter to the boiler is the installer's to change. Everything on the other side of the meter is not.

How to tell what size meter you already have

Look at the dial. Meter sizes are printed near it with a U prefix and a number, or as a Q max figure in cubic metres per hour, which is the same thing said differently. A meter showing Q max = 6 m3/h is a U6.

The published guidance on identifying meter size is short and worth taking at face value:

• U6 is the standard domestic meter and most homes only ever need one.
• U16 is for large properties with heavy demand, the example given being specialist equipment such as a heated swimming pool.
• U25 is for extremely large hourly usage and is very rarely needed on a house.

Source: National Gas, Guidance on identifying your existing meter size

The bit that surprises people: two different organisations own the two halves

The service pipe running into your house, and the position it arrives at, belong to the gas distribution network for your postcode. The meter sitting on the end of it belongs to your energy supplier, the company that sends you the bill.

So nobody on site the day your boiler goes in owns either of them. Your installer works from the meter outlet inwards. If the meter itself has to change, that is a conversation with your supplier. If the supply into the property has to change, that is an application to the network.

The network's own published route through this is explicit about the split. Its early step for a service alteration tells you to discuss your plans with your existing supplier, who will advise whether you need to change your meter.

Source: Cadent Gas, Gas alterations for household customers

What actually pushes a house over the limit

Rarely the boiler on its own. What does it is the total of everything running at once, so the honest version of the question is not what the new boiler needs, it is what the new boiler needs on top of what is already there.

The usual combinations that make an engineer stop and add it up properly:

• A high output combi replacing a smaller regular boiler, which raises the appliance's own gas rate rather than leaving it where it was.
• A gas range cooker, which quietly carries a surprising rate for its size.
• A living flame gas fire that has never been used but is still connected and still counts.
• A second boiler, or a boiler plus a separate water heater, in a house that has been extended or split.
• A long or old service pipe that leaves you short of pressure at the meter outlet before the installation pipework has taken any of it.

The last one is the real one

Meter capacity is a headline number. Pressure is what an engineer measures. It is possible to have a perfectly adequate meter and still fail, because the pressure arriving at the meter outlet under full load is not what it should be. That is a supply issue, not a meter issue, and it is fixed by the network rather than by your supplier.

This is also why the answer is not knowable from a phone call or a form. It is a measured value, taken with the appliances running, which is one more argument for a survey before you commit to anything.

Why it is a timing problem

If the survey says the supply has to be altered, you are joining someone else's queue. The network's published journey for a household service alteration runs: apply online or by phone, an initial preparation stage where you speak to your supplier about the meter, a quote which you have up to 90 days to accept and pay for, a site survey to agree the options, then the works themselves, which take on average six to eight weeks from payment. They call the week before to check the site is ready, and they reinstate turf and planting afterwards while internal decorating is left to you.

Nothing there is unreasonable. It just does not fit inside the week most people are imagining when they book a boiler. If your old boiler is limping and the replacement depends on a supply alteration, the sensible order is to find that out now rather than in January.

Source: Cadent Gas, Gas alterations for household customers

Which network is yours

Great Britain is divided between a handful of gas distribution networks and which one you deal with depends on your postcode, not on who supplies your gas. Cadent, whose published process is quoted above, operates several of those networks and has a postcode checker on its own site. Your supplier can also tell you, and your meter point reference number identifies the connection.

In older Northampton and Milton Keynes housing the practical version of this question comes up more often than the capacity one: a meter boxed on the front elevation, a kitchen extended across the back, and a long internal run between the two. That is pipework rather than meter capacity, and it is the installer's job, but it is exactly the sort of thing that separates two quotes for the same boiler.

What to ask before you accept a quote

Three questions, and any competent installer will have answers:

• Have you checked the working pressure at the meter and at the appliance with everything running, or is that happening on the day?
• Does your price assume the existing meter and supply are adequate, and what happens to the price and the date if they are not?
• If a meter exchange is needed, who is arranging it, me or you, and does the installation date move?

The short version

Most boiler replacements never touch the meter. The ones that do are usually houses where several gas appliances have accumulated over the years, or where the supply into the property was never generous to start with. Neither is common and neither is a disaster, but both are far cheaper to discover during a survey than on installation day.

If you want that checked properly rather than assumed, tell us about the property and we will arrange up to three quotes from vetted local installers who will survey before they price.