Experience with Air Source Heat Pump

Thats interesting because neither of the installers would fit to my north facing garden when I replaced my oil boiler 10 years ago.

Ultimately the cost of the unit wasn’t too bad the extra electric was relatively manageable the final straw was them insisting on sticking it in my front garden where it would benifit from.higher temperatures lost them the work

Did you not consider that maybe they had a point?

Mick_r, I think that you could programmed controls as you describe, will vary by brand. I am currently WFH so keep the house at a reasonable temperature all day and let it cool down slightly at night.

toomba, we have a heat pump rated at 8.5kW output for a 4 bedroom house. The hot water tank is 170 litres, for the previous gas system it was 100 litres. For the use you describe with lots of hot water use this will need to be considered in system design, maybe a larger tank or higher rated heat pump. We run the hot water heating at night only for a couple of hours, you could boost a couple of times during the day. As correctly stated by others, heat pumps are less efficient at higher water temperatures however I can heat water overnight and have a 35oC shower in the evening with no issues.

Trail_rat, where are you? Our heat pump is fitted to a shaded north facing wall in Scotland, never sees the sun and temperatures have been below freezing for days but still working. You do need to take care to ensure good air circulation, if the heat pump recirculates its cooled output air then efficiency will be poor.

i_scorr_cake, I think that you have hit the nail on the head, correct planning and specification is vital as mentioned by others. Many of the issues you have described may be down to poor specification. We have a simple system however it appears to be correctly specified and works.
Difficulties in planning and specification can be overcome with work, it will never be as easy as a gas system I agree.

Did you not consider that maybe they had a point?

Well I’m asking if they did as clearly the op has not got an issue with this issue.

As was yes I considered they had a point and chose a technology which at the time did not have that issue , nor any of the other issues that I was prepared to live with.

Having said, for a thermally efficient home where the house and heating source are designed as a combined system, then they are an excellent idea although water-source and ground-source are functionally superior to air-sourced due to the higher specific heat capacities and more stable temps of their heat-source. As a ‘bolt-on’ retrofit they aren’t a great idea in my view for most homes in the UK.

I’ve never really gotten this argument.

As I see it; At the end of the day you’re paying £x / unit heat.

Either that’s cost effective with a ASHP or it isn’t.

I don’t see why the level of insulation makes much odds, unless the output of ASHP can’t match the heat loss (but that seems like a sizing issue).

If it’s cheaper to run gas, then it’s cheaper to run gas for anything, surely?

@trail_rat not been mis sold any dream but I do apologies if you feel jumped on.I have designed and built my own passive house, built flats to the old code for sustainable homes and completed my passive house consultants training and am very aware of what works and what is marketing bs. It has to be a good thing that more of these sorts of threads come up and get people thinking about how to reduce bills and co2. But I am not convinced that batteries are the answer just yet but I am sure that will change soon.

@Aidy your dead right. Ashp get mis sized a lot. Super insulated homes use so little power it dosnt matter much if they are marginally more or less expensive with gas or ashp as the power needed is so low. My gas bill is £200 a year for heating and hot water. I wouldn’t care if an ashp was 10% more or less efficient. Gas is still widely considered the cheapest way to heat but obviously has other issues.

Gas is still widely considered the cheapest way to heat but obviously has other issues.

This.

Other issues:
climate change and fossil fuels/non renewable.
Not universally available (just ask our friend Trail_Rat). Incompatible with low or zero carbon.
To mention the obvious.

Passivhaus has many plus points but sustainability is not (currently) part of it/one.

Petrol and diesel cars are currently one of the cheapest forms of mass transport… why on earth would we want to change that?

Sure, but from the POV of a mass roll-out, what a constitutes an average home in the UK matters greatly. One appeal of a gas-combi is that you can more or less rule of thumb size it and then just drop it in. ASHPs in contrast demand better planning and specifying. Not an easy thing for your average Bob.

Can’t agree more, your average house builder in this country is going to struggle. There have been several horror stories from social housing with heat pump installations.

@metalheart there have been recent changes to Passivhaus that try and address co2 in energy consumption and peak loading on the grid, but they still don’t seem to be too worried about co2 in construction.

@ajc yup, I’m halfway through an introductory Bitesize course (this week its services, woohoo!).

I don’t disagree with a focus on energy reduction, as whatever fuel source is selected, less is required.

Until the whole circular economy is sorted out it’s difficult to properly address the issue (for instance, ASHP aren’t particular carbon free due to the use of current refrigerants (which are prone to leakage at servicing etc)). I did a #growyourknowledge webinar on it early summer, but can remember it all off pat.

@metalheart do you have any links to further reading or webinars? Aecb have a lot of good webinars recorded for new build and retrofit but I’m not sure if you need to be a member to view them

@ajc it was through CIBSE (and I think being a member also applies). It’s more commercially focused (but the Passivhaus one was about the Agag(?) housing complex one).

I’ll try and remember and check when I’m ‘at work’ tomorrow.

Super insulated homes use so little power it dosnt matter much if they are marginally more or less expensive with gas or ashp as the power needed is so low.

I think that’s what’s weird about people saying you need to have a house super insulated to see a benefit from ASHP. The more you spend on heating, the *bigger* the benefit is that you should see.

I think the idea is that per a given kWh, ASHP is more expensive than a gas-combi, maybe 2 or 3 times more costly in terms of capital cost? So the idea is that you insulate and draft proof your home better, then save some money on the capital cost with a smaller unit?

I think the idea is that per a given kWh, ASHP is more expensive than a gas-combi, maybe 2 or 3 times more costly in terms of capital cost? So the idea is that you insulate and draft proof your home better, then save some money on the capital cost with a smaller unit?

Oh, that makes some sense – thanks. Noone ever says it like that though.

Not chance they’re going to do that, the housing association put ashp into my house with the aid of government grants and neglected to fit any insulation (see my post on previous page). The housing association then got an award for fitting them ffsake.

The government policy at the moment is to green energy supply rather than work hard at reducing it as the reducing energy part is a lot harder. Much easier to tell people to fit ashp and build windmills than deep retrofit the country’s entire housing stock. To have any hope of net zero by 2050 it looks likely we will need to do both and more. A proper deep retrofit is far more complicated than just adding some insulation as there can be air quality and damp issues that aren’t fully understood by many builders. There needs to be training and quality control to reduce the cases as outlined by Somafunk above.

This is funny timing. I have an ASHP (14kw Ecodan) that’s been in this house for ten years. And tomorrow it’s getting removed and replaced with, whisper it, oil combi boiler (as was in before the ASHP). It has been repaired a couple of times now (compressor repairs, re-gassed etc) and is now just not worth spending any more cash on. It feels like a HUGE backward step but the truth of the matter is that in a house that isn’t either designed for it, or subject to major work in terms of the introduction of appropriate insulation, it’s just not economical (nor comfortable even with an Aga and a big wood burning stove).
My old house which we completely renovated from just 4 walls was heated by a 7kw ASHP (another Ecodan) and it was absolutely fantastic. But we spent thousands and thousands on insulation to give us the best chance.

In summary though, and in my experience, (and the right energy tarrif – we were on E7 as thats when the Aga took its power too), they’re a great technology if somewhat limited by the current limitations of building regs relating to insulation and appropriate design of new build homes.

In-laws renovated an old house, and went with ASHP, even with going to town with insulation it cost a fortune to keep the house warm. The FiL wishes he had stuck with oil.

They’re hoping to do a new build next so will be interesting to see which route they go down next.

This is a great thread. Real life experience with ASHPs is hard to come across. Thanks @littledave.

Your willingness to pay more to reduce energy consumption is (as you acknowledge) unusual, and isn’t how they are generally marketed (!). It looks to me – although it isn’t clear cut – that your pump is probably underperforming the promises on which it would have been sold to you if you had got it in the normal way. This really needs to be addressed for them to become more popular. It would be good if the project you are part of generated good data, independent of the people making/selling/fitting them, on real-world, year-round efficiency in UK conditions.

Also, little thing, oil has been generally cheaper than mains gas for a few years now. Heat pumps won’t really compete on-grid if they can’t even compete off-grid.

We nearly got one in a previous home. RHI would have made it worthwhile if we had intended to stay. But without that, the gap to oil was very difficult to properly anticipate precisely but also clearly enormous.

The government is looking into making landlords upgrade properties to meet EPC C or higher by 2028 see here

This is insisting on a fabric first approach so you can’t just put in a heat pump or solar panels and get a better score.
There is talk that this will then also be the case for private house sales. If this goes through it will no longer be a case of which heating type is cheapest, there will be a massive incentive to reduce co2 for space heating and hot water. It is going to cause massive problems with not enough skilled builders let alone how people are going to be able to afford it. Who know if it will actually happen as there is plenty of history in backing out of reducing climate change.

bookmarking thread — ground source might be my preferred option but not evaluated the ground plot yet. Def. some sort of source heating – top of list (more or less) is no gas.

Be good to know if there are reliable advisers / outfits that have the experience and not just marketing spiel.

Currently renting out a house and I’m not looking forward to meeting increased EPC requirements – it just about scrapes through at the moment but on borrowed time (1950s build).

@Kcal the extra expense for ground source over air source is unlikely to be recovered in marginal extra efficiency of it, especially if it is in a low energy house. With ground source there is also some large kit that needs to be inside the house whereas the kit is outside for air source. The issue at the moment seems to be that people that really know what they are talking about are few and far between and often expensive. It is an area that is ripe for cowboy installers. Likely to be a re-run of ’80’s double glazing sales.

thanks @ajc. I’m hoping that by going through decent architects who have some experience in all this there will be independent overview and someone asking the right awkward questions. Yes, low energy house from scratch. good to have input.

It is an area that is ripe for cowboy installers

Sounds like construction in general 😀

@kcal always ask the awkward questions yourself, you can never rely on other people to and its your money. I don’t know why architects always want to specify gshp but I keep talking to architects that do and don’t know much about ashp. Worth having a poke around on the buildhub forum as this is a well covered topic.

An ASHP with R410a is potentially less environmentally friendly than a gas boiler for global warming potential (GWP). R32 systems are now readily available, so anybody looking to get a system installed should check that that this is what they are getting.

If you need a 25kW boiler to serve your house you either have a McMansion or poor thermal performing fabric/leave the doors and windows open. Or you have multiple baths/half hour showers…

not sure this post is serious. I live in a fairly standard largish detached 4 bed 1930’s house. Typical build and construction of most 1930s places. Only insultation upgrades are double glazing and a loft triple layered. Our boiler is a valiant ecotec plus 831 which is rated at 32kw (if the manual is to believed).

When it drops below 0 it struggles to keep the house comfy without being on all day.

anyways on topic. Did a lot of research into these pumps as I’d like to be greener. It was a financial no brainer to stick with gas as long as possible.

I haven’t had a proper quote for external insulation but indicative costs are £10k+ so no chance that is happening either. I think are annual gas / elec costs are approx £125pcm so would take a loooong time to recoup. I got all excited by the green iniative thing the gov announced but it seems largely pointless for us. Maybe underfloor insulation with great disruption is the only thing we could go for

Evening all, checking back in after a day in the (home) office.
Lots of good stuff above, responding to some points in no particular order…

Kcal, we were told that a ground source heat pump would typically require a ground area approximately twice the house area which we do not have (not sure about 1 vs 2 storey houses). You can drill a bore hole but that is more expensive. I believe that ground source is technically better but more expensive and not an option for many.

We replaced a 27kW gas boiler with an 8.5kW heat pump to heat a 4 bedroom detached house with good but normal insulation.
So far in 2021 my heat pump controller is telling me:
Consumed energy: 550kWh (23kWh per day)
Delivered energy: 1550kWh (65kWh per day)
90% of this energy is for space heating and 10% for hot water
These figures suggest a coefficient of performance of approximately 2.7, this is lower that the 3.3 listed on the heat pump data plate, however heat pumps are less efficient at cold temperatures and January 2021 has been consistently cold in my part of Scotland.

It is clear from all contributions and my own experience / research that if you have gas heating then that is is lowest cost option. In almost any situation improving insulation will be better financial and CO2 payback that changing a heating system. I agree that the UK housing stock has scope for significant and relatively low cost improvements to both reduce fuel use and improve quality of life, unfortunately the boring type of actions such as improving insulation on the scale required do not seem to tick the boxes for finding political will in the UK.

thanks @littledave, I have seen the efficiency and payback rough figures for ground source, but yes, we won’t have that much area to play with – looks like air source is the straight forward option. we’re also in Scotland, so solar PV will be a bit problematic and less viable than others – will have more or less south facing (SW I think) aspect though and no obstructions. good to see stuff like this. cheers!

unfortunately the boring type of actions such as improving insulation on the scale required do not seem to tick the boxes for finding political will in the UK.

There are plenty of grants (aka political will) about, there isn’t a shortage of cash. The issue is the cowboy building industry which effectively self regulates. Cavity wall insulation is the latest disaster we are all paying for. Retrofit external wall insulation will be the next.

What should I look for in external wall insulation contractors? My house is a 1960s build timber frame with (mainly) brick cladding. Minimal insulation in the studwork, so I think my only option is external insulation.

(Quick calculation shows that internal insulation would have the dew point in the timber frame.)

What an interesting thread. We’ve had our gas boiler for 13 years. It still works very well and we have a warm house in c15 minutes. It is also a combi boiler so no need for a water tank (Which in a smallish house gives us a decent sized bathroom). We have a 1910s mid terraced 3 bedroomed house with good loft insulation. Running costs are very low (£65 pcm for Gas and Electric)
We’ve looked at alternatives to the gas boiler when it packs in but the numbers soon mount up if we go down the ASHP route. Simple install – £5k ? Some new bigger radiators and fitting – £1500, new water tank and fitting ££??. I could see it costing £10k rather than £2k for a new gas boiler…and a doubling of our energy bills.
A chap I know was looking at an electric combi boiler and the running costs were staggering (4 x that of a gas combi https://www.greenmatch.co.uk/boilers/combi-boilers/electric-combi-boilers )
It is a bit of a minefield unless you really know what you’re looking at but at least the Nations electricity supply will cope with it all….

@littledave – thanks! The real world data is useful.

2.7 is better than I’d expected, given as it’s been a cold month. I imagine that’d average out at well over 3 throughout the year.

Timely thread for me.
I’m in the midst of looking into ASHP to replace an electric boiler. The electric boiler is eye wateringly expensive to run. The bulk of our heat comes from two efficient woodburners, if we were totally reliant on the electric system then I reckon £10 per day in freezing weather would be about the cost we’d be looking at. That’s in a very well insulated ten year old four bed detached house.

I’m loathe to spend the fortune required on the ASHP. Siting is not ideal, and as above, my gut instinct is that the industry is attracting cowboys cashing in. If not cowboys, then enthusiastic, well meaning guys just a bit out of their depth with the tech.

@Murray you need to find a company that will do a good standard of work, and that is what is really hard to know. The external insulation should be fixed with both adhesive and mechanical fixings with no thermal bridge and it is very important to have no air gaps behind the insulation. You need to be asking to see a specification for the works and then keep an eye on the installers. They are likely to want to throw the insulation up and not care about quality of installation as you won’t be able to tell once its up.I would also want to know how the reduction of passage of moisture through the insulated walls is going to be dealt with. You don’t want to end up with condensation build up in your timber frame. This can be modelled but I doubt most companies would do it. You are likely to need a change to your ventilation stratergy at the very least.
If you have a ventilated cavity between the timber frame and brick skin which you probably do then the external insulation will do nothing to help keep the house warm. You would need to put it internally.

10 years ago I was domestic energy assessor for renewables. I should think the tech has moved on a bit but the principles of energy conservation have not changed.

Correctly designed heat pumps systems can be pretty good when installed as part of a holistic approach to D&B.

Retro fit is an entirely different ballpark., As is their use in our climate. Because they are low temperature systems compared to traditional heating systems you need to mitigate against your heat losses as much as possible and use large emitters. Depending on the construction of your building, this has implications for moisture accumulation in places that would never been foreseen when the building was designed.

You need a good installer or even a building surveyor with relevant knowledge and experience, and still, 10 years later, a deep pocket.