[Closed] Experience with Air Source Heat Pump

Thanks for sharing. Might be worth adding that the current proposal for the next big building regulations update is for new homes to not be connected to mains gas.

We’re having one installed in our new home - super insulated, timber framed construction. Advice of builder wasn’t to go for Ground Source Heat Pump as the added costs and complications take 20-odd years for extra payback. We had option of a solid fuel stove as well but decided not to. Will maybe look at PV solar at some point when they come up with a more discrete solution.

Is your ASHP supply separately metered? If not, we’re you wfh before?

Hi Metalheart, no separate metering, the heat pump is on the regular supply and draws a little over 3kw at max usage for short periods.
WFH is new for me as many others. I would expect the gas use to be higher than last year if we were still using it as the house is kept warmer.
Heat pumps are ideal for WFH as they provide lower amounts of heat for longer periods compared to gas.

LitteDave could you expand further on details, is your house old/new inbetween...i.e. what modern insulation standards, what heating emitters UFH and/or rads or something different. Interesting research as you mention to learn more, especially if cost goes up (especially in winter when ASHP less efficient) so will public be sold if costs more to save Carbon, easier to sell the future by saying we will save £££, but not so sure, being cynical and all...my interest is what we can do with old buildings but with long term view.

We installed an air source heat pump as ground source ones require either a large land area or a deep borehole.
We do not have the land and don't fancy a borehole as there are lots of old mines in my area so drilling is risky as well as expensive.

We're on Economy 7 atm, toying between heat pump and pellet burner, bungalow is 90s build with decent insulation.
ASHP will be cheaper to install, but pellets have the RHI payments.

Thanks, the point of asking about wfh is presumably your non-ASHP electrical consumption will also have risen?

I’m interested in actual/real world ASHP experience from a professional viewpoint (experience hadn’t been completely positive and I’m trying to get to the bottom of things as a result). Condensation and frost cycles being main bugbears (albeit in more commercial based environment).

Cvilla, my house is recent build, well insulated 4 bed detached.
We use conventional radiators throughout, larger for use with heat pump.

I agree that heat pumps to replace mains gas will be a hard sell, many will not spend money to increase their costs! We should start with new build, this us happening and other fuels. Ulimately only an increase in cost of gas relative to electricity will drive adoption, CO2 reduction will not do it.

ASHP will be cheaper to install, but pellets have the RHI payments.

Pellets will require significantly more ‘maintenance‘/cleaning.... been a lot of issues with this in LA housing, so much so biomass systems are being replaced.

Are you away from home a lot?

I see this in the future at my house (no mains gas option)

This is why I've gone for solar PV and a battery currently......while.my current oil boiler and tank do their thing. When the boilers up for renewal ashp will look a whole lot more attractive with PV and battery behind it than if standalone.

at the same time I've been beefing up the insulation on the house so we need less energy input

The piss annoying thing about ashp is that I'll have to put the unit in my front garden due to building aspect.

RHI payments are available for heat pumps I think, worth checking out.
Metalheart, in he recent cold snap we have seen the heat pump go into defrosting mode only on one day so our system seems to be working well so far.
My energy use now will be higher than last year at home for lots of reasons, no holidays, home at weekends, no meals out, wfh, more hot drinks so the energy reduction is even more impressive to me.

Do you have any data for the efficiency that it's achieving? Looks like a bit over 200% from the numbers, but obviously wouldn't account for seasonal variation. If the controller had any data, it'd be interesting.

We're here most of the time Metalheart, cleaning and maintenance wouldn't be an issue.

How are you heating your hot water?

We're under increasing pressure to design large healthcare/commercial with ASHP but it is a hard sell, 3kW heat for 1kW electric is only in mild/temperate conditions, you'll be no better than direct electric in winter. Radiators and heating coils all need to get a lot bigger as well!

Requires instantaneous electric heating of water although there are a lot of efficiencies in this that mitigate moving off gas.

We’re under increasing pressure to design large healthcare/commercial with ASHP but it is a hard sell, 3kW heat for 1kW electric is only in mild/temperate conditions, you’ll be no better than direct electric in winter.

Most of the manufacturer data I looked at reckoned on at least 200% efficiency down to around freezing.

I believe the cancellation of new build domestic gas installations has been rowed back on thanks to pressure from house builders. Tories innit? 🤷

@trail_rat how is solar pv and battery meant to help an ashp? At the times of year you generate pv you aren’t really going to need to heat the house.

I think the main problems users have with ashp is that they are often not matched to the spec required in older houses. If you used to need a 25 kw gas boiler to heat the house in winter you will need to replace it with an ashp with a 25kw output.

how is solar pv and battery meant to help an ashp? At the times of year you generate pv you aren’t really going to need to heat the house.

The sun stops shining in winter ?

Solar still works there is just less of it as less sunlight hours. It still removes a portion of the cost -i have solar on my camper already and have witnessed it working and giving good amps in winter for prolonged periods.

How ever I do have the advantage of a south/south east 50degree sloping roof with zero shadowing so it'll do all it can for me....certainly more than if I didn't have anything on the roof. The battery helps me get and store power when it's cheap to heat my house at periods when it's expensive to use the grid.......

Ashp (daiken altherma) fitted to late my 1980's 1 bed bungalow by housing association (DGHP....you useless ****s) about 8 years ago, ****ing hate the thing as fitting it to a bungalow with no wall insulation, no under floor insulation and minimal (same insulation from when built) in attic along with 35yr old thin air gap double glazing means it doesn't bloody stand a chance to offer any heat - in the summer my lecky bills are <£10 week, last week they were £42 as the bloody air pump has to run all the time just to keep the chill out of the house. Within two weeks of it being fitted I opened up the fireplace as the housing association removed it when fitting ashp and fitted a wood burning stove.

@trail_rat the sun does not shine enough in winter to provide any useful amount of power for an air source heat pump. If you have been told otherwise the advice is wrong. I have a 5.5kw solar pv that on most days in winter barely produces more than a couple of kWh and that is just used in the base load for the house. Couldnt you just heat the house at night on cheap power with an ashp and not need the battery?

Not sure what your getting at. Does it or doesn't it generate power?

Net reduction in power is what I'm looking for before I go and start adding further load.

No one said it would power all the ashp.

How ever the battery on the other hand to shift the ashp load largely to offpeak hours.

Couldnt you just heat the house at night on cheap power with an ashp and not need the battery?

Have you ever had storage heaters. Unless it comes with a Chrystal ball you'll end up cold on cold.days and charbroiled on warm days.

The sun stops shining in winter ?

Solar still works there is just less of it as less sunlight hours

Well yes, it does!
In December PV generation falls to about 10% of that generated in June.

I did a little research myself on this last year.

As a retrofit proposition, on your typical thermally-inefficient and gas-heated British home, they are problematic.

On the practical front, you need room for the outdoor unit which is also noisy, room for some kind of hot-water storage, room for some kind of instantaneous heating element (for shower, etc), and then you need larger radiators because it's not efficient to boost the water temp as high as gas combi-boilers go (~70 deg C) Having said that, there are numerous configurations and ideas knocking around including the use of dual-stage heat pumps which supposedly can supply hot water for a shower, etc., but they are still bound by the laws of thermodynamics which is the main problem here; heat pumps become less efficient the colder it gets, and for an air-source heat pump specifically you will have to burn electricity to prevent the evaporator from frosting up when the weather gets to low temps in addition. Expect massive bills and it possibly not even working properly when it's very cold.

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.

My south facing 5.5kw array regularly produces over 30kwh on a summers day and rarely produces more than 3kwh in winter and often below 1kwh. That is not a useful amount of power for an ashp. The only reason I jumped on the pv heating the house crap is because that and the usual battery providing all your energy needs crap was spouted to me by my installer and often gets repeated. Insulation and air tightness with proper ventilation makes the most sense to lower heating bills but people tend to want to buy kit instead.

Yeah if you were going to throw some money at me, I'd externally insulate my period terrace and put new triple glazing in.

We’re under increasing pressure to design large healthcare/commercial with ASHP but it is a hard sell

Someone (pretty well known in the industry) asked me: ‘what happens to the cold air?”.
I’d say you need to ask yourself the same thing. Drop over the coils is approx 6 deg C, if you don’t disperse this properly it will short-circuit and be drawn back in... not so problematic on a 3-4 kW job, not so good with 100kW....

As ever, correct plant and equipment selection is paramount. Select the wrong thing or install it incorrectly/badly it’ll never work properly. There are examples of systems working properly in Scandinavia (which is colder, but mostly drier...). I’m not sure we have sufficient knowledge and experience currently in the Uk.

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...
Money would be much better spent on energy reduction measures.

Also, Nobody is proposing running an ASHP off PV, so please drop that straw man.

PV and batteries are Smart Grid items (to make best use of renewables that generate excess electricity that currently costs a fortune to dissipate). There are some tariffs that will actually pay YOU to take electricity at certain times. Batteries help lop peak/trough usage, and EV’s can also be part of that mix.

But I’m way OT...

Evening all,
Lots of good questions and points above so some responses are due:
I have no direct efficiency data however I can confirm that efficiency is maintained at low temperatures. We are using 20-30kWh electricity while last year we used >50kWh daily gas only.
This is in below freezing temperatures
We heat all hot water including shower using the heat pump, water temperature is lower but the shower does not mix as much cold, still hot enough for a shower, washing up etc.
Our outdoor unit is not noisy, the next door neighbours complain about absolutely everything and have no issue with the heat pump noise!
The heat pump has provided heat and hoot water perfectly well with consistently below freezing temperatures, defrost only activated on one day

i_scoff_cake, you may wish to repeat your research as several of the points you raise are simply not true in many cases. My house is well insulated, however:
My heat pump supplies water for a shower, no supposedly, it does 🙂
No massive bills or not working when cold, see above
A heat pump may not suit you however to dismiss in the terms you did does not provide a balanced service to other forum members, hence why I started the thread to bring forward some real experience of using a heat pump in UK winter for those who may be interested.

The only reason I jumped on the pv heating the house crap is because that and the usual battery providing all your energy needs crap was spouted to me by my installer and often gets repeated. Insulation and air tightness with proper ventilation makes the most sense to lower heating bills

Which we have done and have more in the pipeline. But don't let that stop you. As metal heart says - no one's proposing to run ashp off a solar PV or a battery but it's all part of the system to reduce energy COST at END USE which is my driver....

Going into it with my eyes open having seen the numbers off a colleague's set up who lives near by. sorry if your installer sold you the dream.

Little Dave. Out of curiousity Which aspect of your house is your heatpump situated ?

i_scoff_cake, you may wish to repeat your research as several of the points you raise are simply not true in many cases. My house is well insulated, however:
My heat pump supplies water for a shower, no supposedly

I'm assuming you have a two-stage system or two heat pumps then? Again, more capital cost.

Do you have a brief summary of how your house is constructed and insulated? I do stand by my claim that air-sourced heat pumps are not a good 'bolt-on' solution for your average crappy British home. As you imply, you need a well insulated home and even then it's not particularly economic because of the large capital cost, even if from a carbon POV it's a decent solution.

As ever, correct plant and equipment selection is paramount. Select the wrong thing or install it incorrectly/badly it’ll never work properly. There are examples of systems working properly in Scandinavia (which is colder, but mostly drier…). I’m not sure we have sufficient knowledge and experience currently in the Uk.

I believe that Germany has led the way re heat pumps for several years now, but specifically ground and water-source. Local/district heating systems with heat sourced from rivers or ground-water are very good solutions.

Interested in this as we hopefully move into a new build in summer with decent insulation and an ashp. Bit disappointed the small developer hasn't also gone solar pv in place of tiles on a nice south facing bit of roof.

How "smart" are your ashp controls? Does it do things like run more in the winter daytime when ambient air is warmer? I'm considering that as a strategy as there looks to be decent internal thermal mass in the construction (don't think it would work well in say a timber frame where there is minimal mass inside of the insulation).

A guy at work lives in a country cottage backing onto a canal. I keep trying to persuade him to go gshp and lob the coil in the nice ready made water filled trench 🙂

Interested to read of your real experience of living with an ASHP littledave. How big is the heat pump and size of dhw tank?
We are in the middle of a self build and going for air source heat pump with ufh on both floors. House very well insulated.
One concern I have is our hot water requirements as we have 3 kids and all like showers.

Trail_Rat, my heat pump is fitted on a north facing wall, no issues so far.
i_scoff_cake, no we have a single, single stage heat pump, properly sized for the house. All hot water for the day is heated on low rate overnight power for about 2kW. My house is about 10 years old cavity brick, double glazing etc, well insulated but normal not passivehaus or similar.
There is no such thing as an average home, each installation will be different.

For avoidance of doubt for the wider community, heat pumps can operate effectively in below freezing temperature and heat hot water also. No special tricks, just a suitably specified system for the house.

I am not a heat pump salesman, just sitting here in cold weather, warm and with plenty of hot water while reading opinions to the contrary. 🙂

Local/district heating systems with heat sourced from rivers or ground-water are very good solutions.

Absolutely, buts as I said before

I’m not sure we have sufficient knowledge and experience currently in the Uk.

Local area heat networks is the way forward. Needs to be done properly though... 🤪

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

Has the technology moved on that much in 10 years.in another 10 when my boiler needs replaced again maybe the local engineers will have caught up

Oh, and thanks littledave, nice thread. 👍

Local/district heating systems with heat sourced from rivers or ground-water are very good solutions.

At the time 2011, the largest GSHP installation in Europe was the one for the One New Change shopping centre in the City of London, this used the underground aquifer to the provide the heat which was transferred using collectors Incorporated into the piles upon which it was built.

no we have a single, single stage heat pump, properly sized for the house. All hot water for the day is heated on low rate overnight power for about 2kW.

As you say, you're not a salesman. A single pump, fixed compressor ASHP won't be efficient at two output temps. Maybe you have something fancier like refrigerant reinjection, variable speed, or something?

There is no such thing as an average home, each installation will be different.

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.

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.