Everything I Know About Air Source Heat Pumps
If you’ve been looking into ways to heat your home more efficiently, you’ve probably heard a lot about air source heat pumps (ASHPs). Some people swear by them, others say they don’t work well in older homes, and there’s a lot of conflicting advice out there.
After working on high-end residential projects in London, I’ve seen air source heat pumps in action—when they work brilliantly and when they can be a bit of a headache. So, here’s everything I know about them, the good and the bad.
What Exactly Is an Air Source Heat Pump?
An air source heat pump works a bit like a reverse fridge. Instead of cooling things down, it extracts heat from the outside air (even when it’s cold) and transfers it into your home for heating and hot water. It doesn’t burn fuel like a gas boiler, so it’s considered a greener option.
It runs on electricity, but because it moves heat rather than generating it, it’s much more efficient than traditional heating. In the right conditions, ASHPs can produce three to four times more heat than the electricity they use. Importantly though, they still use electricity and electricity is more expensive to buy than gas (for the time being!).
The Good Stuff: Why Air Source Heat Pumps Are Worth Considering
1. Lower Running Costs
If you’re switching from gas, an air source heat pump can lower your energy bills. They’re incredibly efficient, and when paired with a good insulation setup, they can be cheaper to run than a gas boiler in the long term. Heating your house with an air source heat pump works out around 10 - 20% cheaper than heating it with gas so straight away, you’re saving money but not a huge percentage.
2. Government Grants Help with the Cost
Heat pumps aren’t cheap to install and run to around £12 - £25k to install but in the UK, there’s the Boiler Upgrade Scheme (BUS), which offers up to £7,500 towards the cost. This can make switching to an ASHP a lot more affordable which brings it inline with cost of installing a conventional gas boiler and cylinder. There is also no VAT charged on heat pumps etc.
3. Better for the Environment
Unlike gas boilers, air source heat pumps don’t burn fossil fuels, so they have much lower carbon emissions. If you power them with renewable electricity (like solar panels or a green energy supplier), they can be nearly carbon-neutral.
4. Works Well with Underfloor Heating
ASHPs don’t heat water to the high temperatures of a gas boiler, which means they work best with underfloor heating or large radiators. If you’re planning a high-end renovation, this can be a great opportunity to upgrade your heating system at the same time. The pipe spacing of the UFH should be 100mm rather than the normal 200mm and I would double the size of the radiators to achieve similar heating in the space.
5. Low Maintenance & Long Lifespan
Once installed, an air source heat pump doesn’t need much maintenance—just an annual check-up. They last around 15-20 years, which is longer than a typical gas boiler.
The Downsides: What You Need to Know Before Installing One
1. Upfront Cost Can Be High
Even with the government grant, a typical ASHP installation costs between £8,000 and £15,000. If you also need to upgrade your radiators or insulation, the cost will creep higher.
2. They Work Best in Well-Insulated Homes
Because ASHPs run at lower temperatures than gas boilers, they work best in homes with good insulation and airtight construction. If you live in a Victorian Terrace like me and your house is draughty, you should address the building efficiencey by improving your windows, doors and insulation first—otherwise, the heat pump will have to work harder, reducing efficiency.
3. Not Always Cheaper to Run (If Your Electricity Tariff Is High)
While ASHPs use less energy overall, they do rely on electricity. If your electricity price is high and gas is still relatively cheap, you might not see huge savings on bills—at least in the short term. Cheap electricity is often from fossil fuels so you may end up using fossil fuels to power the air source heat pumps deleting your green credentials.
4. Outdoor Unit Needs Space (and Can Be Noisy)
Unlike a boiler that sits indoors, an air source heat pump needs an outdoor unit, usually mounted low on a wall or placed on the ground. While modern units are much quieter, you’ll still hear a low humming sound when it’s running—something to consider if you’re placing it near a bedroom window. I’ve known them rated similarly to the sound of a gas boiler or a kitchen fridge which sounds great but you wouldn’t want your neighbours fridge next to your bedroom window.
5. Not Always Ideal for Older Homes
If you live in a Victorian or Edwardian home, you will almost certainly need to upgrade radiators and insulation for an ASHP to be effective. While this isn’t a dealbreaker, it’s an extra cost to factor in.
So, Is an Air Source Heat Pump Worth It?
The answer depends on your home. If you’re doing a renovation or new build and can design the heating system around the pump, it’s a great choice—efficient, low maintenance, and future-proof.
If you live in an older, less insulated home, it can still work, but you might need additional upgrades to get the most from it.
At Bloom Builders, we’ve worked with air source heat pumps on high-end residential projects and can advise on whether it’s the right fit for your home.
📞 Get in touch if you’d like to discuss your options—we’re happy to help.
