Air Source Heat Pump

The younger sibling of the ground source heat pump (GSHP), the air source heat pump (ASHP) is an exciting development in heating technology. They operate on the same principles as the under-ground alternative, but draw thermal energy from the air rather than underground – air at ambient temperatures is passed over a finned heat exchanger and heat energy extracted into the evaporator of the heat pump. ASHP’s release up to four times more heat energy than they consume in powering their various components and so offer an energy efficient, sustainable heating solution. They are best coupled with well insulated, energy efficient buildings and under floor heating systems.

Currently (summer 2007), a 6kW ASHP costs around £3,500 with a larger 12kW pump weighing in at about £6,000. This excludes the cost of the distribution system such as an under floor heating installation.

As air is the medium from which thermal energy is extracted, the installation of an ASHP is relatively straightforward – there is no need to dig extensive trenches or drill the borehole necessary for a GSHP. The pump is sited at a suitable distance from building and connected via pipe work buried in trenches. ASHP’s are designed to operate with minimal noise pollution.

Author: mbc

This is the story of MY barn conversion

27 thoughts on “Air Source Heat Pump”

  1. Glad to be of help …

    I believe that these systems do work in the middle of winter, but that they use more electricity the colder it gets and that can make them less environmentally and economically friendly than alternatives.

    The jury is still out…

  2. I replaced my old oil fire boiler in 2006 with a Air Source Heat Pump (there is no gas in my village). I have a 20yr old property with 200 sq m of floor space (100 sq m per floor) with a 12Kw heat pump and I have not needed any oil to heat the house. I used up the last of my oil in October and removed the oil tank. My AHP costs for heating (DHW works in tanded with the immersion heater) is £600 p.a. It used to be 3000lts of heating oil, now at 60p per litre. I estimate payback to be between 7-10 year

  3. I live in a chapel conversion built in late 18th century. It has a 20ft high ceiling in main room and this room is 36 ft x 36ft. I installed underfloor heating in this main room and it works well (can get room to about 21 c in winter previous year with rads 18.5c tops). All other rooms have conventional rads and are all warm enough. The problem I have is with oil consumption. I use 1200 ltrs a month from approx Oct – May. Yes seriously 1200 ltrs a month and at £0.60 a ltr I’ll soon be going bankrupt. I have insulated under the ufh and in the loft but there is nothing I can do to the walls (grade 2 listed building with lath and plaster walls) I cannot decide if air source pumps is the way to go or something like a wood pellet stove. I need about 33kw (and due to heat loss running this almost constant) Anyone got any ideas how I can save money in the long term?

  4. We are thinking of replacing an old oil fired boiler with an air source heat pump. Does anybody know whether you have to replace it like for like in KW or does the air source heat pump not have to be as big any info appreciated

  5. At last a web site with useful info on this!
    We are also looking at air source as an option in the future. We have a stable/barn conversion built 2003 with v good insulation. Have twin coil h/w tank in place but not gone for solar water panels yet as payback period is v long. Conventional rads in all rooms and currently condensing oil fired boiler. Would want to replace this with suitable system to provide heating and hot water.
    Concerns are
    noise – have heard negative comments on this.
    Payback period/comparison on cost c/f oil.
    Any comments/suggestions of other web sie info sources appreciated.

  6. Thanks Alan – I try to help…

    I think you should reconsider solar water as the payback is now reasonable & getting more so as fuel costs increase.

    Personally, ASHP’s don’t do it for me – I was going to install one, but my ‘green’ friends are anti them as they consume large amounts of electricity, their complexity and servicing costs also put me off. As basically air conditioning units in reverse the just seems too much that can go wrong – especially in our crazy climate.

    Have you thought about a Pellet Stove? – green, mean and reasonable to run!

  7. I have recently installed both solar and a ground source heat pump before the “real” cold weather arrives. I shopped around and found a company on the internet called solar 7 based I think in stockport. I found them to be extremely helpful and happy with the end result.
    I have done some calcs and hopefully I will get a payback similar to Peter Rycrafr above of somewhere around 7 years.
    I agree the jury is still out for the winter months but I will keep you posted later this year ! Fingers crossed

  8. We too installed a 16kw heat pump in Nov 2008. We have a large barn approx 400 sqm with ufh to all floors. We were in the process of changing over to Economy 10 and received an electricity bill 2 days before Christmas – £750.00 for 4 weeks. Our SAP report quoted that we would spend approx £1,000 pa on running the heatpump. Where has the calculation gone wrong? We spent in 4 wks almost what our annual spend was predicted to be. Has anyone else experienced this? Our insulation is well above what is required for building regs etc and we only run the temp at 19 c. Apart from turning off for some of the day, which is not recommended how do we minimise the costs. At this rate we will certainly not be recouping our costs back.

  9. Diane, sorry to hear that your heat pump is proving so expensive … could you get someone other than the installer to give it the once over? It guess it must be running pretty much constantly to have consumed that much electricity. Could you run it for only part of the day?

  10. We have recently purchased a Victorian Range for our old Farmhouse up in the hills. Believe it or not we do not have a chimney but we do have an outside wall to put it on. Our house is stone and the usual very thick walls. Have you any advice on going about building a chimney, reasonable price. We are not a listed building but are in a greenbelt area.

  11. Linda, we’ve been through a similar process ourselves, with thick walls and no chimney. We’ve opted for a twin wall flue system running internally. That lets us avoid any planning issues (our plans allow for an internal chimney), keeps as much heat as possible inside the building and avoids external aesthetic issues as the flue would need to run up a prominent gable end wall. Hopefully it won’t be too much of an eyesore internally.

    There’ll be more on this on the site soon…

  12. I Have Purchased an old 18th century farmhouse and wish to fit an air source heat pump with underfloor heating will it work well under a solid oak floor ?

  13. Tim ,

    Hope you’re heeding the warnings of heat pump costs given above?

    You can lay a solid oak floor on top of the layer of screed in which your under floor heating will be laid (under floor heating needs the thermal mass of the screed to store heat and operate efficiently). You’ll need kiln dried oak as oak with any moisture in it will warp and crack potentially quite drastically as the UFH dries it out.

  14. I run a small restaurant and our electricity cost is £1200 per month most of which is hot water.
    Can someone tell me if an air source heat pump would be suitable alternative for my hot water needs? bearing in mind demand is quite high?
    Can it work in conjunction with a mega flow hot water cylinder?
    Ideally I would like someone to come out and conduct a survey and do some calculations, anyone available? We are based in Clapham South London.

  15. Not personally sure that an ASHP is your solution, but I’d certainly encourage you to consider solar hot water panels.

  16. Solar thermal will not be as effective for the restaurant water heating because there is no guarantee that you will have the sun shining when you need to replenish the hot water, then you are getting into expensive backup heating.

    Why not get it right from the start, a small ashp to a good sized cylinder will give good run time (no cycling) and give excellent economy.

    …and all the hot water you need.

  17. Matt, solar thermal will work for say (pessimistically) 60%+ of the time and will require additional inputs – so not perfect but cheap to run after initial costs.

    What I don’t like about ASHPs is the unknowable costs & variable efficiency – how efficient will it be? What ratio of electrical inputs to hot water output will you get? The only way to manage those electrical input costs is PV, but then the costs of PV are still prohibitive … there’s no one perfect solution.

    As the restaurant is in London mains gas will be the most cost effective method of heating water – but then your green credentials go out the window. But mains gas against ASHP, I must admit I think I’d still go for gas at the moment.

  18. I wish i had found this site last year! I have an ASHP and Solar panels in my property and i am now living in poverty and have a huge outstanding balance on my electricity account due to both of these sytems! I strongly advise anyone who is considering having these systems installed NOT TO DO IT. For my 3 month elec bill over the winter, i was over £1000!!! The system is NOT adaquate for the cold winter months whatsoever. It cant cope and burns more electricity. My systems pumped so many units through my main elec meter than it caused my meters to basically die 3 years in a row, March every year when the milder weather came back in.
    I can only advise that anyone thinking of using these systems not to, but if you are prepared to pay out EXCESSIVE amounts of money running it, then thats your choice. I have had over 3 years of fighting to have my systems taken out and im just about there, but i have still had to suffer another freezing cold winter with the ASHP 🙁 I could honestly write a book on the problems i have had!!

  19. I’m in a barn conversion with a GSHP supplied by Ice Energy 3/4 years ago for hot water and underfloor heating. After Years of wrangling they also fitted an ASHP free of charge having admitted they undersized the GSHP originally. Marginally warmer now, however I still have the fundamental problem that when someone has a shower, the system switches to heating the hot water back up ignoring the underfloor temp, just as it switches back to that and starts getting it warmer someone else turns a hot tap on and off we go again. It never, despite all adjustments gets over 40c but it needs to be 45c+ to really make hte underfloor work properly. Is 40c all I can expect?

  20. Michelle,

    I can only say that you have had your system poorly designed and fitted. Installed properly, air source heat pumps will keep you warm and save you money. My mother installed one and it saved her £1,000 per year. No problems with warmth etc. Im a developer and Ive installed them into 4 apartments. Bills come to £500 per year for each apartment. That includes cooking and lighting too! Again no warmth problems. I was so impressed, I set up a heat pump biz. Just going through the accreditations now, UKAS done now waiting for MCS for product and installer.

    I would imagine your system has some sort of back up heater like an immersion which is switch on permanently. Maybe this is for your hot water? Theres a serios problem there but Im sure easy to resolve. My web is Thought I would be honest to tell you about what I do!

  21. Michelle, just another note, our heatpumps use approx 3kw per hour. If this was used on full for 24hrs a day, this would use 72KW. You can biy elec for 7.5p per kw so the max you could pay with this system is £5.40. This would be £450 per quarter. Thus you must also have some sort of immersion or a very, very large house!

  22. i have ftted a air source heat pump an its all working but the heating water does no reach a temp for the floor to heat up is this normal and how can i fix it thanks

  23. Doesn’t sound like it is working to me Scott…(It might come on, buzz and consume some electricity, but it’s real job is after all to heat water) what temperature is the pump managing to get the water up to?

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