Should I replace my gas boiler with an air source heat pump?

Should I replace my gas boiler with an air source heat pump?

Probably yes — but the more important question is whether you should do it now, or wait until you’ve dealt with your building fabric first.

You can go straight to a heat pump?

There’s a persistent myth that switching to an air source heat pump (ASHP) requires a wholesale overhaul of your heating system — new radiators throughout, major pipework, significant disruption. In practice, this isn’t necessarily true.

One of our clients put it to the test before committing to anything. They turned down their existing gas boiler’s flow temperature to between 35°C and 40°C — the range within which a modern ASHP operates most efficiently — and ran it through a heating season. The result: their house stayed warm. Only two radiators proved insufficient and needed replacing. Everything else worked fine.

We’d suggest any client in a similar position try this first. It’s a low-cost, low-risk way to understand what your existing system can actually deliver before spending anything significant. Speak to a heating engineer before doing so — they can advise on whether your boiler and controls will run at reduced flow temperatures, and what to watch for.

But fabric first is still the right answer

Switching to an ASHP without addressing the building fabric is a bit like fitting a more efficient engine to a car with holes in the bodywork, or with brakes insufficient to stop you. You’ll still lose heat through poorly insulated walls, draughty floors and leaky windows — just slightly more efficiently generated heat!

Improving insulation, eliminating draughts, and upgrading windows and doors where possible reduces the amount of heat your building needs in the first place. That changes everything downstream. A better-insulated house needs a smaller ASHP. A smaller ASHP responds more quickly to temperature changes, runs more cheaply, and doesn’t have to work hard to compensate for avoidable heat loss.

There’s a third component worth considering alongside insulation and an ASHP: MVHR — mechanical ventilation with heat recovery. As you tighten the building fabric, you need to ventilate deliberately rather than accidentally. MVHR extracts warm stale air and uses it to pre-heat incoming fresh air, recovering up to 90% of the heat that would otherwise be lost through ventilation. We’ve written about it in detail here.

Done together — fabric upgrade, correctly-sized ASHP, MVHR — this is a genuine whole-house performance transformation, not a boiler swap dressed up as something bigger.

The policy question: is a gas boiler ban coming?

Honest answer: the situation is genuinely unclear, and anyone giving you confident dates is probably overstating what’s known. What is certain is the gas industry is pushing hard to prevent a ban, and convincing people hydrogen is around the corner as a silver bullet - it is not. We’ll write about hydrogen in another piece.

The previous Conservative government proposed ending the sale of new gas boilers from 2035. The current Labour government has indicated it won’t pursue that hard ban, instead focusing on incentives — most notably the Boiler Upgrade Scheme, which ant the time of writing still offers £7,500 towards an ASHP installation.

The Future Homes Standard, still being finalised, will effectively exclude gas boilers from new builds through efficiency requirements rather than an explicit ban, without necessarily naming gas as prohibited. Further policy tightening for existing homes will follow, though when and in what form remains genuinely open.

What is not in doubt: the direction of travel. Every government since 2019, regardless of party, has moved toward low-carbon heating. The pace and mechanism are contested. The destination is not.

The saleability argument

This is the most under appreciated reason to act, particularly if you don’t plan to stay in your home long-term.

A house with an ASHP, improved insulation and a strong EPC rating is an easier sale. Mortgage lenders are increasingly factoring energy performance into lending decisions. Buyers — particularly younger buyers — understand and value low-carbon credentials in a way that simply wasn’t true a decade ago. Dealing with this now, while you have time and budget to do it properly, is significantly preferable to being delayed during a sale negotiation.

Where to start

Run the flow temperature test, with a heating engineer’s input. If your existing radiators cope, a straight ASHP swap is viable with minimal disruption. If you’re undertaking wider refurbishment — or planning to stay long-term — use it as the opportunity to take the fabric-first approach: insulation and airtightness first, then size the ASHP to the reduced heat demand, then add MVHR. 

The question was never really whether to move away from gas. It’s how carefully and over what timescale you make the transition.

If you are thinking of moving away from gas, a phased strategy can be developed for any property. If you are considering a whole house refurbishment, a deep-retro-it, this is the most effective and efficient time to carry out works. For either route we can help, please contact us for a discussion.