Trying to work out if an Air Source Heat Pump is worthwhile

[DampedOut]

Long time lurker, first time poster. Have always enjoyed the forum and reading about other people's adventures and misadventures with their older properties.

I was hoping to get people's insight and advice about a dilemma that's cropped up about how to heat a large property that we think dates to the late 1700s. My mother bought it a couple years ago on the cheap because it needed a lot doing and it's getting there (slowly).

Anyway, I had read that heat pumps are best suited to well insulated houses and are no good in draughty period properties, so an oil boiler seemed best a couple years ago.

Two things have made me wonder if I should reconsider that assessment. One is the Hitachi Yutaki specs: (https://www.hitachi-hvac.co.uk/ranges/heating/yutaki-m and https://electricheatwarehouse.co.uk/products/hitachi-air-source-heat-pump-pack-7-5kw-heating-only?variant=5411328622625).

The other thing is what this guy has to say. Here is the text of the interview and here is the podcast.
https://www.houseplanninghelp.com/wp-content/uploads/2013/02/Justin-Broadbent.pdf
https://www.houseplanninghelp.com/hph017-can-a-ground-source-heat-pump-make-an-old-house-energy-efficient-with-justin-broadbent-from-isoenergy/

Is thermal mass a genuine thing in old properties with solid stone walls? This house certainly has them and as more work gets done, it should breathe more and they should be easier to heat up and keep warm with vapour permeable insulation etc.

The house uses 6000L of oil per year for a 90s Rayburn (5.5L per day) and a new-in-2018 Bosch oil boiler. I calculate the heating needs as being about 40,000 kWh per year. She has some illnesses that are much worse if she's in a cold home, so she likes to keep it at 19º and that's the consumption at that temperature 24/7 for a year. Her bathroom has an electric shower so when we're not visiting she switches HW off, I think. With visitors, HW comes on 3x a day for 30 minute blocks and that's more than enough to heat up the whole tank. It usually switches off after 15 minutes during that 30 minute run-time even if she has 2 visitors who are taking baths and draining the tank.

If the government will pay back the cost of an air source heat pump over 7 years and there's a savings in running costs, it seems an obvious swap. Plus it would mean ditching a gigantic oil tank that has a growing crack and needs replacing (left by previous owner). Price for replacing that oil tank has been quoted as £1000. The house is large, about 15 radiators. 9 are upstairs but the climate isn't so bad, it doesn't go below 0º often (in Cumbria). Rayburn will be disconnected in the next 6 months or so as well. So I am left wondering if a Hitachi heat pump could do the job without the oil.

Why is swapping in an air source heat pump a bad idea? No space for a ground one; it's a middle of village house. Have people had much luck with them? Is thermal mass in period properties a unicorn? All comments welcome! Sorry for the long first post.

 

[DampedOut]

Forgot to say a few things in the overly long post above.

The house is already set up for three phase electricity, so that's something.

In the 80s it was very heavily modernised. The ground floor has cement slab in most spaces, a suspended timber floor elsewhere. Lots of gypsum. We're not really interested in underfloor heating—apart from anything else, I think it disqualifies you for the RHI. The ethos has mostly been to remove modernisation wherever possible, but just bit by bit.

The house has a horrible cement render on the front that dates from the 20s (there are photos). Any breathable insulation would be something like EcoCork for the outside facade if there's planning permission to remove the cement facade—which is, of course, causing loads of damp. Definitely loft insulation—thinking wool. As for internal wall insulation and floor insulation, probably not.

Anyway, all to say, the goal with the house is not to remove historical features and make it super insulated. If anything, it's to remove all the gypsum and cement plaster on the inside over time and try to get the stone walls retaining and giving off heat as well as breathing again.

But the approach to how to make the house more efficient is going to depend on whether thermal mass in solid stone older properties is a fairy tale or not...

 

[Flyfisher]

A few thoughts and random observations:

back in 2007 when we started our period property 'adventure' we had very limited oil-fired heating via an old Rayburn cooker/boiler.
I'm completely out of touch with oil prices these days but I remember that our first tank full of oil cost around £350 and lasted five weeks - which set me thinking about alternatives.

For a while I became quite keen on a ground-source heat pump as we have plenty of space for the ground loop and the c.300% efficiency was an attractive proposition. Until I discovered I could get connected to mains gas for £295 and that on a per kWh basis it was about 3x less expensive than electricity. In other words, the running costs would be similar but the GSHP installation would be around £10k vs around £2k for the gas connection and a gas boiler. So I chose the mains gas route, supplemented by a wood stove with a back-boiler connected into the heating system. The more wood we burn the less gas we use and fortunately we have a lot of free wood.

I was suprised how little it cost to get connected to mains gas, but I assume that there's no mains gas in your village?

Coincidentally, our annual gas usage is also 40,000kWh (39,329 for the last rolling year), which has cost us £1,252. I'm out of touch with oil prices so have no idea how that compares today.
Our electricity costs 13.6p per unit overall, so 40,000 units would cost £5,440. Assuming an air-source heat pump would be about 300% efficient, that should mean an annual electricity usage of around 13,333 units = £1,813. For 350% efficiency it would be £1,554 and for 400% efficiency it would be £1,360. I vaguely recall that ASHP efficiencies fall as the air temperature also falls, whereas GSHP efficiency remains relatively constant for obvious reasons. But I've not really followed HP technology closely for a decade now so I don't really know about the latest state-of-the-art.

As for draughty period properties, I'm not really sure why that would affect ASHPs particularly more than other forms of heating. The more heat lost from a property, the more heat needs to be injected in order to maintain a given temperature. I'd expect that to apply to any form of heating. The last time I checked, the various government grants for renewable or 'greener' heating systems were only available for houses with a certain energy-efficiency rating and above (I can't remember which band). Ie, modern, well insulated houses could get grants for solar PV and solar heating etc whereas less energy-efficient houses (which often means period properties) could not. Frankly, I don't really understand the reasoning behind this because if a less energy efficient house uses more energy (which it typically will) then surely it would be better for that energy to be renewable? ie, if the heat source is renewable - such as solar thermal - then surely there is little or no environmental impact if the houses uses more energy than its new-build neighbour? But them's the rules and the policy makers are unlikely to be reading this :wink:

You ask: "Is thermal mass a genuine thing in old properties with solid stone walls? This house certainly has them and as more work gets done, it should breathe more and they should be easier to heat up and keep warm with vapour permeable insulation etc. " Yes, thermal mass is definitely a 'thing' but I'm not sure this makes things particularly easier (or more difficult) in terms of overall heating requirement. If the walls are very damp then it will certainly have an bad effect (you don't want to be wasting energy heating the moisture in the walls), but if the walls are dry then they will act as a form of 'storage radiator'. This will introduce a 'lag' to any changes in the house temperature, but I don't think it should affect overall energy consumption per se. You'll soon get used to switching on the heating much earlier in the morning than normal so that the house (and walls) are up to temperature by the time you want to get up and, conversely, the heating can be switched off much earlier than normal and the house temperature will be retained for much longer than normal. Whatever 'normal' is!

Basically, thermal mass will dictate how quickly a house heats up and cools down and insulation will dictate how quickly heat is lost and therefore how much energy must be used to maintain a constant temperature. I think those basic principles apply regardless of what form of heating is used. While heat pumps are undoubtedly more efficient than some other forms of heating, they also have the inherent disadvantage of using the most expensive form of energy, ie electricity. So much depends on what is actually available in your area and whether you define efficiency as being the lowest cost, the lowest kWh requirement or the lowest carbon emissions.

As for thermal mass, I've become quite a fan of UFH based on our experience of the floor in our kitchen extension and I'm about to start work on our last large room, which will involve a new limecrete floor (our 4th LBC application was approved last week! ) in which I'm planning to install UFH. I'm hoping to hook this up to a solar thermal system, though I still have to resolve issues with where to locate the solar thermal tube panels, but that's a work in practice and won't stop me installing the required pipework in the new floor slab.

Anyway, bit of a ramble - I hope there are some points of interest.

 

[DampedOut]

Thanks for this great and really informative reply! Lots to think about here.

So, she’s paying about the same electric rate as you. This past 12 months, the 6000L of oil ended up costing pretty much an even £3,000. I’m expecting that to drop to £2,000 once the oil Rayburn is disconnected, but the exact drop can’t be known until it happens. It got a very thorough tune-up last summer so it’s running in good order, and I think it probably is 5.5L a day.

You guessed right, the house is not in a mains gas area. The village is about 600 people, so I don’t think that would change either.

My mother just got two quotes for ASHP from a local and a national company. I think the house is 290 sq.m. First quote was for a 16kWh HP and install with some extra and new “more efficient” radiators for 15-17k (I’m skeptical about this being worthwhile). The national company said it would need 2x 12kWh HPs (because of the drop of efficiency in deep winter) and install for 30k. Both companies said the government Renewable Heating Initiative?Incentive? would pay out 12k over 7 years. So it’s not much incentive, actually. Not surprising, I suppose.

It may be worth thinking about using a wood burner to supplement the heat in the winter. The first company doesn’t work with Hitachi HPs, and I need to look into the ones they use instead (Grant). The RHI scheme ends next spring, so unfortunately there is a bit of a rush on figuring it out. The house is also rated E so focusing on loft and ground insulation as well as cutting the damp wouldn’t go amiss. Luckily, the chancellor has promised 5k grants on insulation from September if you spend 7.5 (but it only has a 12 month window).

The other issue is the savings may not be that much yet. If annual oil goes down to £2,000, even if HPs drop the running costs to £1,300, that’s only a £7,000 saving over ten years. So we’re talking about spending up to £30,000 to save £7,000 over ten years and get £12,000 back. The 2 HPs don’t make sense, unless I’m missing something.

Better option is probably the local company, deal with insulation, and supplement the heat with a woodburner and an Aga that’s in the post. The Aga is one of the new electric radiant heat models that was on sale last month. It will cost about £500-600 a year to run. Anyway, maybe it’s worth going that way and upgrading to double HPs when the first one wears out in 10-15 years.

I hope all this info is helpful to other people thinking about the same thing, but thank you, Flyfisher, for your reply. Curious if you have any more thoughts re: those scary quotes! Lot to think about, especially UFH and costs you’re seeing too. Would be very nice to be in a gas area! Curious when they’re going to start trialing Hydrogens in the gas mix too. Biggest worry I suppose is the government deciding to beat up on oil heating users in order to reach their climate change targets.

 

[paulc]

It did cross my mind to install a GSHP or ASHP system here and I looked at the day to day costings - Bottom line is either system could easily end up being very expensive to run. They work best with low flow/return temperatures, so UFH and low temp radiators are needed. If the system is poorly specified and/or installed, it is all too easy to end up with an expensive electric powered heating system that costs an earth to run.

If one is going to spend upwards of £15K, it might be worth looking at a biomass boiler if there is space for a wood pellet/chip store.

 

[Bogart]

Just offering my observations having been in an old draughty property with airsource. Yes it does work but I would never have airsource, groundsource yes.
Reason is groundsource is equally efficient throughout the year. Airsource is at its least efficient when it is needed to be at its most efficient in winter.

 

[Flyfisher]

thank you, Flyfisher, for your reply. Curious if you have any more thoughts re: those scary quotes! Lot to think about, especially UFH and costs you’re seeing too. Would be very nice to be in a gas area! Curious when they’re going to start trialing Hydrogens in the gas mix too. Biggest worry I suppose is the government deciding to beat up on oil heating users in order to reach their climate change targets.

Scary quotes - that's the biggest problem with all the 'alternative' energy systems I looked at a decade ago. Even if the systems worked, the payback period was very long and my feeling back then was that the capital costs were likely to reduce as the technology improved and the take-up increased, driving down manufacturing costs. It's the old thing about 'early adopters' paying a premium (which I've done many times in the past with 'consumer' technology - £650 for a 2 megapixel digital camera anyone? :lol: ). In the end, I was fortunate to have the mains gas option so I 'chickened out' of a hard decision. If not for that, I was reluctantly veering towards oil, which is at least proven although the fuel cost is obviously subject to high volatility so it's a a bit of a bet - although the £10-15k capital cost savings compared to some other option at least gives a bit of a head start on the savings front.

As for adding or migrating to hydrogen in the gas grid, I've read various things about this, mostly in terms of feasibility though I've not read much about its efficiency. As I understand things, the hydrogen would be produced via electrolysis, which is a proven technique so no doubts there. But is it really efficient to convert electricity into hydrogen then burn that hydrogen in the home for heating compared to just using the same electricity directly for heating? After all, converting electricity into heat is an almost 100% efficient process. Also, I've seen more reporting of the move away from gas heating than I have about using hydrogen, with some reports saying that gas heating in new build homes will be banned from 2025: https://www.bbc.co.uk/news/science-environment-47559920
My bet is that everything will migrate towards using electricity as our primary energy source, but over what period and at what price is anyone's guess.

I agree with you that oil prices are at the whim of government taxation and that the migration to electricity might be 'encouraged' by increasing fossil fuel taxes rather than by electricity prices coming down but it's really all a guessing game that we're pretty much forced to play. My feeling is that if we have to bet on something then it's best to keep our stake as low as possible. Thus, choosing mains gas might be the wrong bet in the medium term, but it's a cheap bet so we lose relatively little if we have to later change. Choosing, say, a biomass system might also be the wrong bet in the medium term but it's a high stake bet because of the high capital investment and long payback period. I guess an oil system would be somewhere in between. It's all very difficult and the bottom line is that heating is expensive!

Probably my most cost-effective heating investments have been multiple zone valves, so that we only heat the rooms we actually use in the winter, thermal underwear and thick jumpers!

 

[Flyfisher]

If one is going to spend upwards of £15K, it might be worth looking at a biomass boiler if there is space for a wood pellet/chip store.

I looked at biomass boilers but they seemed a bit 'industrial' to me. Fine for a farm setting or small industrial unit, but not so easy to incorporate into a domestic setting, even if the space is available for a 10 or 20 ton fuel store.

 

[Flyfisher]

Just offering my observations having been in an old draughty property with airsource. Yes it does work but I would never have airsource, groundsource yes.
Reason is groundsource is equally efficient throughout the year. Airsource is at its least efficient when it is needed to be at its most efficient in winter.

Yes, I've read that about ASHPs though have never actually experienced it first hand. When you say 'least efficient' do you mean in terms of not actually being effective at heating or that the energy efficiency drops significantly so that it becomes more expensive to run. The latter would be bad enough but the former would make it almost useless.

 

[Flyfisher]

Just one other thought. We all know that heating with mains electricity is expensive, but solar PV systems seem to be one 'alternative' technology that is fast becoming mainstream. Even without the most lucrative FIT deals are no longer available. A neighbour has recently had a 6kW system installed on his south-facing roof, complete with a home battery system. He told me it was around £5k, though I don't know the details of the deal or any FIT arrangements. I wonder if a solar PV system powering electric UFH would work out cheaper to run than other alternatives? Or even solar thermal panels linked to a 'wet' UFH system?

Having said that, we are on a period property forum and roof-mounted solar panels (PV or thermal) raise other complications for many of our properties.

 

[Me!]

Just offering my observations having been in an old draughty property with airsource. Yes it does work but I would never have airsource, groundsource yes.
Reason is groundsource is equally efficient throughout the year. Airsource is at its least efficient when it is needed to be at its most efficient in winter.

Yes, I've read that about ASHPs though have never actually experienced it first hand. When you say 'least efficient' do you mean in terms of not actually being effective at heating or that the energy efficiency drops significantly so that it becomes more expensive to run. The latter would be bad enough but the former would make it almost useless.

I have previously worked in an office that had air source heat pumps that could work in either direction to provide heating or cooling. Presumably it is possible to specify a system with sufficient capacity to cope with all eventualities, however in this particular case it very definitely fell into your "almost useless" category. Not nearly enough power to warm the building on a cold day, or to cool it on a hot one.

 

[DampedOut]

This stuff is all good to know, thanks for the replies!

I emailed the CO to see about solar panels on the house but I wouldn't be surprised if that's not going to be possible because it's a conservation area. The RHI also only gives you money back for solar thermal panels that heat hot water and nothing else. The more I look into it, the less feasible or useful the RHI seems to be. It's also good to know about ASHPs having mixed reviews. It just seems like the technology isn't there yet to really warrant worth the upfront costs.

I'm also inclined to look for changes that are either good value or small losses if they don't work out. So it seems worthwhile to address the damp, to increase loft insulation (finding a breathable thicker one is is going to be its own challenge) and look for other things to do that will have a big pay-off for what they are.

Curious what saved the most heating costs for others as they renovated their properties?

 

[Bogart]

Just offering my observations having been in an old draughty property with airsource. Yes it does work but I would never have airsource, groundsource yes.
Reason is groundsource is equally efficient throughout the year. Airsource is at its least efficient when it is needed to be at its most efficient in winter.

Yes, I've read that about ASHPs though have never actually experienced it first hand. When you say 'least efficient' do you mean in terms of not actually being effective at heating or that the energy efficiency drops significantly so that it becomes more expensive to run. The latter would be bad enough but the former would make it almost useless.

Like any heating system has to be big enough and it will do the job. As airsource needs to extract heat from the surrounding air obviously is a much harder job in winter. Much harder to extract X amount of heat in winter as opposed to summer, unit will run longer and harder. The massive advantage of groundsource is that go 6 ft down into the soil and the temperature remains the same.

 

[jamestyler]

Just to offer my experience...


We have a stone built house. 250sqm.

Installed ASHP in Oct 2019 after lots of research. We’re going to install GSHP but the cost to install slinkies or boreholes was crazy. Yes they are more efficient in the depth of winter but if it costs and extra £15-20k to install will you ever really benefit from that slight improvement?

Also I didn’t like the fact that if the ground loops etc were
Miscalculated it’s can only show up years later when you lose efficiency due to sucking too much heat out of the ground. At least with an ASHp there’s unlimited air! Plus it’s harder to resolve, worst case with ASHP the installer can upgrade the heat pump if they calculated wrong.

We opted for a 14kW Mitsubishi Ecodan. It’s the model that will maintain its output down to -20c so no need to overspec. Make sure you get a full heat loss calc so you know your energy usage. Don’t guess. We made a few holes in walls to check insulation.

Our house is a stone outer, brick inner and 50mm Polystyrene backed plasterboard internally. We decided as we were having new floors laid to add a retrofit UFH system with 25mm XPS. It’s very minimal insulation but takes the chill off the floor when turned off.


Overall very happy. We have one 1/4 of the house that’s insulated differently and has greater heat loss. That has oversized radiators and does lag a bit. It can take 12 hours to increase by 1c if we run at 40c which is more efficient than 50c.

Don’t underestimate this. We therefore leave it running at 19c during the day and 17c overnight. If it’s particularly cold outside we have to leave it at 19c all day. That’s cheaper than pushing the water temp up.


The main rule with ASHp is to run the water temp as low as poss. So start by leaving temp at constant 24/7. If it heats the required temp after 24hours you can turn the water temp down slightly. Keep doing this until you reach a point where the room struggles to heat then whack it up 1-2degrees. Then you know you’re running it at the lowest setting. Ours is generally between 38c and 45c depending on outdoor temp.

Insulation is important but so is draughtproofing. A can of squirt foam comes in useful!

Our bills last year were approx £200-300 in electric per month over the winter. Avg £150 all year round. But that’s for everything, including cooking and hot water.

We have a lot (7!) external doors downstairs, some of which don’t fit great so my plan is to replace some with fixed windows this year and I think that will help the heat loss quite a bit.

 

[Bogart]

Not sure what you mean by sucking too much heat out of the ground, can you elaborate. These systems are ideal for UFH but in my mind useless for radiators, they have to be so oversized. Blown air units probably sit between the two but who wants the noise of fans all day.

 

[DampedOut]

I'd heard about this with GSHPs, that they can make the ground colder. I'd read that if they're installed too closely together or with tight loops, they can draw so much heat from the ground that you actually end up with a cold patch above and around them. But today I read something further about how because the heat in the ground builds up over time, you can actually drain it too fast and the ground you're drawing from will become colder and colder over time so that the heat pump has to work harder and harder to generate heat, constantly making the situation worse and worse until I assume it can't work any more. It's buried in this sort of FAQ: https://www.icax.co.uk/Heat_Pumps.html

Turns out the Domestic RHI should continue until March 2022, so still a bit of time to make decisions. I also read that borehole GSHPs require a 5m distance between them and buildings, which makes things a lot trickier in a village location for those. I need to look into it more. I haven't totally given up on an ASHP, but I think it will be a good idea to try to make efficiency changes in the house first (insulation, fixing the damp, maybe bigger radiators) and see what difference that makes on oil consumption.

Thanks JamesTyler, this gives me hope! Can I ask, what's the weather like where you are? And who did the heat calc for you?

 

[Bogart]

Have now read that article yes I now understand what it is on about. If the ground loop is designed correctly this should not occur. We considered GSH a couple of years back but the more and more I thought about it decided no.
Firstly the cost was going to be £40k plus. Due to the amount of fluid in the system, all the rads, the flow and return to the loop and the loop itself an expansion tank of some 300L required. And finally after radiator calcs done for a lower flow temp than the oil boiler 23 new radiators need and some were 'large'. Cost would have been north of £50k. I can get a lot of oil for that!

 

[DampedOut]

Wow, that is a lot of cash! And I agree, you can get a lot of oil for that for sure.

I guess my worry is just that the government is going to force us all off oil sooner rather than later. And I don't think they'll be nice about it. I was looking into what they're going to replace the RHI with and it turns out that it will be a lump £4,000 payment per household when you install a renewable heating technology. I don't think that's going to help anybody with anything much really given how high the costs are. But apparently the RHI got criticised for not being good value for money after people with the upfront cash for 15k+ changes went ahead and often got more money back than they laid out before some changes were made to the scheme around 2015. And after 2022 everyone who didn't have the money or motivation is going to get back a lot less, even though only 90,000 people did the RHI when it was really paying out. I guess I don't think what's coming is very fair for people who are cash strapped, couldn't get a loan, couldn't be bothered or don't have a lot of liquidity, but that's the way it is with government schemes. :/

Ok, my opinion on gov't policies aside, the drop in grant/assistance definitely has me thinking if changes to the house lower the heating bill this year then it will be time to figure out how to do an ASHP next year before the cut-off.

 

[jamestyler]

Absolutely do the insulation first. Not only will it means cheaper running costs and better comfort but you might need a smaller ASHP so win/win.

We get the cost of our install and heat pump back via RHI so really just pay the cost of running. Which was cheaper than oil (maybe not this year!)

We’ve just added Solar so that will help offset the cost in the Autumn/Spring a bit.

 

[Bogart]

Speaking of the government it strikes me as odd but this new cash dole out is only available to those who get loft insulation or air/ground source at same time. So you cannot install DG unless you get someone
to put some insulation in your loft. As it is all means tested I think, cynical maybe, it is just a paper exercise.