Why we can't have an air source heat pump

As part of our quest to make our house more efficient, we've installed solar panels, a battery, insulation, and all the other stuff you're supposed to do. The next step is working out if we can reduce our dependency on gas.

Octopus Energy (join and we both get £50!) offered to send an engineer around for free to assess our property for suitability for an Air Source Heat Pump (ASHP).

The engineer was friendly, knowledgeable, professional, thorough, and just full of bad news!

Here's a short summary of the issues they found:

  • Siting of the ASHP. It can't be in view of the road, so it needed to be in our back garden.

  • Space for the ASHP. We had just about enough space on our back wall - given the existing pipe-work, doors, etc.

  • Surface for the ASHP. Needs to be on concrete or similar. We have decking (which, to be fair, could be removed).

  • Distance from neighbours. The ASHP makes a bit of noise - about as much as a washing machine. Regulations say that it has to be at least 8m away from a neighbour's window. Not possible in a narrow terrace.

  • The ASHP runs on electricity. Quite a lot of electricity. We'd need our main fuse upgraded and new tails. Both are possible - but the space we have in our utility cupboard is already cramped. Fitting in another distribution box would be disruptive. As would laying new cables from the front of the house to the rear.

  • ASHP requires a hot water tank. At least 100 litres - but probably closer to 200l. That's at least 200Kg of weight. While I think our loft could take it, their structural engineering calculations differ - and who am I to argue?

  • So where would the tank go? We'd either have to lose a bunch of space in a room or remove a cupboard.

  • Because ASHP run at a lower temperature than a conventional gas boiler, it was likely that our radiators would need to be upgraded to larger sizes.

  • On the plus side, the ASHP would work flawlessly with our Tado smart thermostat. Which is nice.

So, there we have it. For our tall and narrow terraced house, an ASHP just isn't possible without a lot of disruption and a significant change to the installation regulations.

Next steps

We've been experimenting with Far Infrared Heating. Solid panels which directly heat the room. They're less energy efficient than a ASHP - but they provide heating pretty much instantly. They can be individually controlled, which should lower their cost. They're also plug-and-play so don't require any domestic remodelling.

We might move our gas hob to induction. That'll be quite expensive - and we don't use a lot of gas when we cook.

Hot water is the next big thing to tackle. An electric shower would work well. Using solar power to feed into the shower would work. But boiling a huge bathtub's worth of water is another matter. We either need a water tank and something like an iBoost to divert solar into an immersion heater. Or a heated tap. Or a not-yet-invented microwave boiler.

A little bit of a setback to our dreams of a more efficient house - but not the end of the world.

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40 thoughts on “Why we can't have an air source heat pump”

  1. Arachnoid says:

    A recent factfilled post on facebook in regard to Air Source Heat Pump gave a price of between £9000 to £15000 per household to upgrade ( so virtually as new installation), based on trials already completed on various sized homes. Yes a large and remote from neibours, space for the unit is required for the heat exchanger which is basically a large radiator and even larger fan to drive the outside air through it.So yes very limited use on many new homes that are very close together.

  2. Thank you for sharing your experience. That's useful to know. I felt similarly disappointed that on my narrow terrace house I don't have enough flat roof for solar panels, so it least you got that!

  3. I did wonder if it was possible to share with a neighbour (if you had a willing neighbour) but I guess it would be complicated for bills/legal reasons.

  4. Kai says:

    I had this thought 4 years ago just as I was renovating our new home. After tonnes of research, I had settled on getting carbon electric paint for our ceilings to act as energy-efficient, space-saving, highly controllable, instant electric radiators. The intention was to keep our home warm in the winter months using just passive daylight solar power which would heat up all our internal surfaces to keep them cosy for human usage as if they were storage heaters like floors, walls, and kitchen worktop surfaces. That all fell through we we could not even find an installer of the technology within a 50 mile radius.

  5. “Because ASHP run at a lower temperature than a conventional gas boiler, it was likely that our radiators would need to be upgraded to larger sizes.”
    You can test this by running your boiler at a lower temperature, which will have the benefit of making it more energy efficient

  6. I had been wondering about the per-room fitted aircon units, and whether they’re sufficient and efficient enough to heat the house in the winter well. Then you only need smaller outdoor units that could be mounted half way up the wall.

  7. says:

    In the Netherlands, "hybrid" heat pumps that switch to gas for hot running water (no hot water tank necessary), and for heating during the coldest few days of winter (no radiator upgrade necessary), will become mandatory for existing builds by 2026. Considering the similarities between British and Dutch post-war home construction (we're the only two countries who ever thought terraces were a good idea), climates and gas infrastructure, I'd be surprised if this wasn't a viable option for British homes.

  8. Absolutely frigging bonkers. We’ll all roast but the aliens who find the remains will greatly approve of how we didn’t put stuff in the cartilage of the buildings.

  9. It comes down to whether it makes sense to heat the whole house with the gas fired boiler, or just heat the space you’re in with the IR panels. Can work very well for some, with significant savings, but certainly not for everyone.

  10. djh says:

    Thanks Terence, I always enjoy your blogs/talks about upgrading your house with greener solutions.

    I've always been put off the ASHP route due to the electricity cost, although admittedly combining it with solar + battery might help offset that somewhat.

  11. Brendan says:

    Have you looked at solar thermal systems to heat water? They are much more efficient than PVs powering an immersion heater.

    1. @edent says:

      We've taken a look. The problem is much the same as with PV to immersion (which we previously had). We only need significant amounts of hot water in winter. And there isn't much solar energy during the long cold winters.

  12. Sam says:

    I had a ASHP installed in a Manchester terrace last year, so it not impossible. I think you might have the 8m bit wrong, ours is certainly not 8m away from a neighbours window. From what I read at the time there are requirements for it to be "permitted development" (meaning that you don't have to get planning permission) and this includes it being at least 1m away from a boundary, https://www.planningportal.co.uk/permission/common-projects/heat-pumps/planning-permission-air-source-heat-pump . But we did have to get some of our radiators upgraded, and give up the space under the stairs for a water tank.

    1. Sam says:

      And not as loud as a washing machine. Not much louder than a gas boiler, though it runs for more of the time.

  13. If it’s any consolation, we live in a detached house and have all the same problems, except we already have a hot water tank. A battery is next on our list, the solar panels have been going ham these past couple of months, I reckon we’d have had almost 2 months “off grid”

  14. Brett Viren says:

    It sounds like (no pun intended) that the 8m requirement kills any idea of a heat pump.

    But, if that can be solved, then using a "minisplit" system would avoid all the problems related to heating up water. Plus it would give you cooling in the summer.

    If the actual "8m" distance is a function of noise output, perhaps a minisplit system would enable you to choose a lower powered heatpump to be in spec. Of course, these kinds of noise laws vary greatly but minisplits are used in very densely populated areas.

    It may bring its own problems, such as the need to devote some internal wall space to the head unit and to bore a small hole through to the exterior.

  15. Foxy says:

    Hey, a few responses from experience of living with a heat pump...

    "Surface for the ASHP. Needs to be on concrete or similar." Ours is wall mounted.

    "The ASHP makes a bit of noise - about as much as a washing machine." Our Mitsubishi Ecodan makes very little noise. Nothing like a washing machine.

    "it was likely that our radiators would need to be upgraded to larger sizes." Possibly but we've had ours installed on our existing old rads with microbore pipes. They heat up pretty well! and over time we'll see if we need to upgrade any of them. Also with a terraced house you benefit from good insulation on both sides so it may be fine.

  16. Martin Hammond says:

    Air conditioning units can also heat, my mate has one in Spain. I had one in the custody office in Manchester nice and warm in the winter. Another mate who is a time served electrician tells they use no more electricity than a domestic fridge two units can be run off one pump cost about 3k.

  17. John Badger says:

    In USA heat pump water heaters are quite popular. Without the VAT they can come in under £2k. There are a few advantages such as no need to run main unit all
    summer, even can help cooling the property, very little alterations to hot water system needed, sort of plug and play as control system self contained.
    Now this I see as a biggie, in cold weather when you need heat the most it doesn't burden the main unit, could be used with economy 7. Or else could be used when daytime temperature is highest. Love to hear comments.

  18. Tim M says:

    Have you thought about a Tepeo ZEB?
    I looked into getting an ASHP and couldn't because of space and microbore pipes. I now have a ZEB and it's pretty much a direct replacement for a gas boiler.
    The only down side is that it is the size of a washing machine....

    1. @edent says:

      It looks interesting - but requires a hot water cylinder. We don't have one as we use an on-demand boiler.

      1. Tim M says:

        True, although we were lucky and already had a hot water tank.
        That said, we don't use the ZEB for hot water as the immersion is more efficient (and can also be free from our solar PV).
        Is there an option to have an electric hot water on demand type system as well as a ZEB?

      2. Bob Pugh says:

        Downside is the efficiency is only 1/4 that of an air source or air to air heat pump . Even if you have loads of solar why use 4 the power? Electric boilers only makes sense if there is absolutely no other choice.

  19. Simon says:

    An alternative to a water storage tank is a heat battery, works in a similar way, storing heat for later release into hot water, but is more complicated to set up and a bit more expensive, they do weigh a lot less than a tank and take up less space however.

  20. Domhnall Dods says:

    Our ASHP makes about the same noise as a desk fan. Our neighbours were concerned it would be noisy so we brought them round to show them once it was installed.

    "very nice but can you turn it on so we can hear how noisy it is?"

    "it's already on"


  21. Malcolm says:

    I'd look to get an ASHP which heats the air directly rather than a water system. All the problems of water tanks and radiators go away.

    A new host of problems appear such as how to run the coolant to every room and where to put the heads.

    You also continue to use gas for your hot water and you aren't eligible for the government grant. You also can't plumb it into underfloor heating.

    On the plus side you'll have air-conditioning, smaller outside unit that could be wall mounted (maybe) and no need to change any plumbing. You can even fire up the boiler on those extra cold days if needed.

    1. Bob Pugh says:

      The only downside is no free money from HMG as they consider it air conditioning rather than heating. It is efficient cheap and doesn't cause anything like the disruption of a full wet ashp if your system needs lots of upgrades.

  22. Marcus Rutherford says:

    Having received Terrence's blog I thought you might want to read the following as an alternative to heat pump technology.
    Below, is the internet link/shortcut to the official online written evidence submission publications for the Environmental Audit Committtee's call for evidence for Accelerating the transition from fossil fuels and securing energy supplies.


    Please note that my personal submission of evidence, is mostly focused on a solution to the very many complications and inconveniences regarding retrofit, especially expense, disruption and skills shortages. In addition to domestic and non-domestic space heating, our technology is also highly relevant in a number of ways to the decarbonisation of space heating in industrial and public buildings, especially schools, colleges, universities, and, especially, listed buildings, as well as having huge potential for very high energy efficiency process heating (this being only briefly hinted at in ATFF0041, as a one-liner, due to the restrictive 3000 word count) in numerous ways. Cheers.


  23. Sorry to hear it. I tried to get a quote for an ASHP for my slightly unconventionally extended Victorian terrace a few weeks ago but the engineer refused to quote on grounds it was too complex an installation. We have nowhere obvious for the external unit to go that doesn't involve very long pipe runs indoors.

    1. @edent says:

      We don't have enough space outside for the loops to go under our garden. And there are too many pipes in the way to allow for a borehole.

  24. says:

    I recently spent quite a bit of time considering alternatives to a gas boiler for our home. I was very open to the idea of installing an ASHP. Had one vendor proposing a hybrid solution
    (ASHP and gas boiler) that seemed reasonably financially viable, but I really wanted to remove my dependency on gas over time so didn't take that option. Then our aging boiler broke and due to its age and make, replacement was basically the only option offered. I decided to go around the loop again, looking at pure ASHP solutions. My (probably a little rough) calculations suggested that a retrofit would end up costing us about 10x the cost of a new gas boiler and would probably end up increasing our energy costs (due to the disparity between the cost of gas and electricity per kWh). I wasn't overly put off by needing to get a loan to pay for the expensive installation, but the likelihood of then needing to pay more for fuel on top of servicing that loan kinda killed the project and we ended up getting a replacement gas boiler.

    We have a reasonable PV array and have now fitted some better logging to enable me to build the case for battery storage with the other half. Initial calculations suggest its very viable in summer (we'd be drawing virtually nothing from the mains during the summer months), but probably wouldn't have much impact during winter (where the limited data I have suggests we generate a small fraction of the power we do during summer).

    At some point I'd love to move to an induction hob too. I have had some experience with using one and I think the only thing its struggle with (after a short period of adaption) may be stir-frying in a wok, though I've heard that's possible with a good induction hob.

  25. John Badger says:

    I'm looking at installing a Dimplex Edel. I have 10p.economy 7 and it takes 3.6 kwh to heat 200 litres, 7°c ambient, COP 3.36. COP 2° ambient 2.64 , -7° 2.25.

  26. @Edent Oof, bad news indeed! The 8m rule is news to me, d’oh.Just heard about a new Bosch(?) unit that fits in the loft like a Velux window, facing outward but flush. This might help with space & distance to neighbour.Didn’t know Octopus offers free surveys, another great tip!

  27. says:

    @Edent @paul When our combi boiler died recently, I also looked in all ASHP and replumbing to use Octopus Go as an iBoost type solution. No tank and the all the associated disruption you detail made it just not worth the cost. I'm taking solace in a much more efficient combi boiler. Aside: two difference plumbers dismissed ASHP and solar + immersion and said hydrogen was the future. I didn't get into that argument.

  28. Iain says:

    We got ours from Octopus, and had our survey in July 2022, installed August, cost £3500 (after gov grant).

    It's at the front of the property, facing a road.
    It's not 8m from next door's windows
    It's not on concrete, we dug a shallow hole and filled it with gravel, but it can be wall mounted.
    It makes hardly any sound, just a gentle rumble like a fridge.
    We had a few of our rads upgraded as part of the contract


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