Air source heat pumps

[Talllbloke]

Hey chaps, somewhat off topic I know, but I’m wondering whether anyone has any experience with replacing a combi boiler with an air source heat pump? Specifically, I’m wondering about cost for a 16kw system for a large semi – online there are some ballparks in the £8-£12K range, whereas the first quote I’ve had is almost £20K.


Anything else to look out for and experience with particular manufacturers would also be useful.


Thanks!

 

[phil4]

No direct experience, but a neighbour of mine has one.

The only issue occurs when it's really cold and they have the heating on for very long periods. It then ices up externally, and stops working.

Our office heating works in a similar way I think, A/C units run in reverse. We get a similar problem in that the external units ice up in the winter, and it then has to defrost. As it does so it can't heat.

 

[MrBadger]

Get a survey from a reputable company as they are not direct replacements for existing on demand heating systems. Don't accept an oversized system without having the figures from a decent survey and analysis - an oversized system will kill the efficiency. Just be wary that the CoP (efficiency/performance) is the bit that makes up the difference between buying (for example) gas at 3p and electricity at 14p. Don't think that you can just run it like an existing on demand gas boiler system - you may have to run it for long periods of time in many retrofits - the state of insulation and construction of the house will have a huge difference. Know what you are buying in to and that it operates very differently - goes back to the its not a direct replacement etc. We are very well insulated and run an mvhr (ventilation with heat recovery) but still don't think we would get away with a heatpump without further major work. Make sure you are very well insulated and air losses/drafts are minimal- this forced our hand on the mvhr. And finally, ask the same question in renewable energy/green build forums.

imho.

 

[Limey]

I only had electric storage heaters before (renovation), but I replaced with an ASHP.

Has the 16kw been specified for you?

I have a 12kw with a 3 bed semi. 180l water tank and a mix of rads/ufh.

Modern units should have external immersion heaters that clear ice.

Larger rads might be needed as temps are lower, but depends what you've got.

Mine was about £10k-£12k for a Panasonic aquera and tank. MCAS pays about £4k back over 7 years.

 

[Avendit]

We've had loads of work done on our house starting in Jan, including the replacement of our 20+ year old gas boiler. We have a large 5 bed and have a 12kw ASHP for water and heating.

Most useful thing we did (based in scotland) was talk to Energy Saving Trust Scotland, who got a guy out to the house to do a Home Energy Improvements Report that offered 4 different 'packages' of approaching improving the house's efficiency. That then also had what loans and grants would be available to us and how to apply for them. Suggestions were new boiler, ASHP, solar and ASHP+solar. Each analysed against our actual usage for energy and CO2 emissions.

That made it clear that just whacking an ASHP on the house wouldn't work and we would need to add more insulation than we had to make it work. The previous owners had taken advantage of all the available free installation, but due to the design of our house this left lots of bits of the house not well insulated. We had to fix that, then add the ASHP. We have now done spray foam insulation over the top of the house and the under floor is due to be done soon. That along side a new extension that is carefully built (but not pasiv Hause by any means) seems to be working fine. Due to age we needed new rads anyway, if your system is built around a modern boiler you may need to upsize them? We were coming from an old single pipe heating system so our replacement rads are about the size we are used to, but that may be a factor for others.

As we were replacing the kitchen anyway we also moved to an induction hob (flipping brill btw), and cut off our gas and got rid of our meter, which I'm well pleased with

In short, insulate and really really draft proof, then ASHP. It works and is as much like magic as the tesla seemed like when new.

 

[NorfolkMustard]

No experience but have looked into it, I wholeheartedly support what’s been said above. Insulate first, don’t replace like-for-like (I.e. the kW output)

this guy on Twitter is an installer and speaker/trainer, seems extremely knowledgeable and balanced https://twitter.com/kenbone44?s=21

 

[Avendit]

And finally, ask the same question in renewable energy/green build forums.

imho.

any recommendations for these btw? I'd love somewhere to geek out about these things, but struggled to find anything not associated with a manufacturer or behind a paywall (looking at you passivhause forums)

 

[Radders]

I have one, installed as part of my new build, as mentioned above run on lower temps so UFH works well with these, if not larger rads. Insulation and air tightness of property important, I'm running a 11kw for my place approx 240 sqm and more than enough, when looking around other companies said may need 16kw but the guy who installed done all the calcs and said the 11kw was fine, he was spot on, and as said above shouldn't over size. Had mine 2 years and never had an issue with it or with it freezing, heats house fine, I have UFH throughout. Was a bit dubious at first with it coping in winter but is fine, obviously not as efficient in winter but warmer weather makes up for it, i.e very efficient for heating HW in summer months.

I'm a surveyor and see these going in all the time mostly Mitsubishi (which is what i have).

Government currently have a £5k grant that I would imagine you could look at, or the RHI scheme which I have, I get back about £7k over 7 years.

Cost me about £10k for supply and install of ASHP, pipe work between ASHP and cylinders 2x 300l unvented cylinders 1 for HW and other as a buffer tank for my heating as I think works better with one. (Mine was excl VAT as self build)

 

[Glan gluaisne]

Our house is heated by an ASHP, a small one, rated at 7 kW output, but which is still way too big for our needs (maximum continuous heating we need in winter is around 1.6 kW). It's very efficient at producing low grade heat, up to about 40°C, but efficiency drops off dramatically about this output temperature. At 55°C, it's maximum working temperature, it is less than half the efficiency of when it's running at 40°C. Consequently, we don't use it for hot water at all, only heating (and cooling). We have an underfloor system set into an insulated concrete slab, that works very much like a large storage heater. This can both heat the house in winter and cool the house in summer, as pretty much all ASHPs are reversible (they have to be to defrost) and so cooling in hot weather is a bit of a bonus.

Personally I'd only consider using an ASHP for hot water if we had space for a much larger hot water storage cylinder, such that we could manage with hot water at ~55°C. Even then the heat pump efficiency would be poor when heating the hot water, but still a bit cheaper than direct heating of hot water using electricity. I doubt hot water heating costs would be cheaper than a gas boiler, though.

If heating with an ASHP then the heat emitters in the house need to be able to work at a low temperature. We run our floor with an inlet temperature of about 28°C, and a floor temperature of about 22°C, perhaps up to 22.5° in very cold weather. That makes for good efficiency from the ASHP, but wouldn't work with radiators. If using radiators, then the size if them all need to be increased, to maintain a similar heat output at the much lower flow temperature from the heat pump.

 

[MrBadger]

any recommendations for these btw? I'd love somewhere to geek out about these things, but struggled to find anything not associated with a manufacturer or behind a paywall (looking at you passivhause forums)

No recommendation but In the past I have used navitron (a supplier run website but fine if you don't go discussing where to buy non navitron kit) when specifying my PV. In addition, there is build hub but no experience of it other than it was once recommended by a knowledgeable member.

 

[Talllbloke]

Has the 16kw been specified for you?

Yes, that's what's been proposed. But, it's an old house with solid brick walls so not terribly well insulated or insulatable.

Thanks for all the answers so far!

Anybody have any knowledge of Nibe systems? Swedish company...

 

[MrBadger]

But, it's an old house with solid brick walls so not terribly well insulated or insulatable.

There's a chap on navitron forum I mentioned to may have had similar circumstances. Sorry, can't remember who.

 

[M3noob]

Yes, that's what's been proposed. But, it's an old house with solid brick walls so not terribly well insulated or insulatable.

Thanks for all the answers so far!

Anybody have any knowledge of Nibe systems? Swedish company...

There are external insulation systems available. You render over the top so unless you're in love with bricks, it could be an answer.

I had ASHP 40 years ago in the States. I wondered when you guys were going to catch up

 

[Radders]

Yes, that's what's been proposed. But, it's an old house with solid brick walls so not terribly well insulated or insulatable.

Thanks for all the answers so far!

Anybody have any knowledge of Nibe systems? Swedish company...

not too much knowledge but seem to be very good systems.

 

[Avendit]

A cousin up in Aberdeen had the gap between his lath+plaster and the stone of his house filled. He says it works, but I'm pretty sure it will make a serious condensation risk that may cause problems later. EST paid for it tho, so presumably the installer is taking the risk...

My parents are in an old stone house and I couldn't see how to do it easily without changing the outside, which would ruin their old stone house. But tackling the roof, under floor and as many drafts as possible will get you a long way, but it's a big job. Thing is, ASHP or gas, these things are all a damn good idea anyway. It's the drafts that make you feel cold, not the actual temp of the room.

Drafts are hard tho, you can't really pay people to sort them. You have to track them down yourself, then decide if it's a diy or pro problem for each area of concern. This is why we went spray foam, tackled insulation and drafts at the same time.

 

[OneTinyFish]

We had a visit from an Air Source Heat Pump installation company recently. They said it was only worth pursuing if we could dramatically improve our insulation.

The trouble is, the core of the house is from the middle ages and modern insulating materials and building practices wasn't on their agenda.

We have LPG gas central heating and multifuel burners. And dogs and cats and jumpers.

Would Air Source Heat Pump be useful >anyway< as a slight improvement rather than to be relied upon as the sole source of heating?

 

[Glan gluaisne]

IMHO, it's well worth considering using an air-to-air heat pump, rather than an air to water one, if only looking at heating/cooling, and not hot water as well. The performance of modern air-to-air units seems very good indeed. I DIY installed a cheap Toshiba unit just over a year ago, just for cooling, but it can also deliver heat just as effectively. Not hard to install, either. Took me about half a day, with the hardest part being lifting the outdoor unit (which looks just like a tiny ASHP) up on to brackets high on an outside wall. Total cost came to about £800 for a 2.5 kW unit, but that includes the cost of the vacuum pump and gauge set that I bought to do the installation properly (much cheaper for me to buy all the kit to use just once, than pay someone the silly money they wanted to install the thing).

 

[Avendit]

We had a visit from an Air Source Heat Pump installation company recently. They said it was only worth pursuing if we could dramatically improve our insulation.

The trouble is, the core of the house is from the middle ages and modern insulating materials and building practices wasn't on their agenda.

We have LPG gas central heating and multifuel burners. And dogs and cats and jumpers.

Would Air Source Heat Pump be useful >anyway< as a slight improvement rather than to be relied upon as the sole source of heating?

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Depends on your motivation. If you are doing it because you love the property and want to be as green as possible and are not too worried if that costs you a bit extra, then its worth looking at further. If you are a spreadsheet kind of person that need to see a ROI over x years, its probably going to have to be a pretty complex spreadsheet to get this one over the line. Our logic was capital investment was fine (doing an extension and replacing whole heating system anyway), as long as it wasn't going to be drastically more to run we were going to do it.

Stone buildings 'work' very differently from modern houses - the thick stone of the building is supposed to act like your heat store. I wonder if you could work with this and use them as others use concrete slab under floor heating or something, but you are probably looking into a really niche use case here. Really interesting, but not a bolt on replacement...

Thing to look at is your heating needs in kilojoules (rough guess is on an EPC, or a specialist will be able to give a more accurate number), and see if there is a way to meet this need with an ASHP, or some obvious steps you can take to reduce the requirements so that you can meet in the middle. Or if LPG is getting expensive or you want to reduce the CO2 impact of that, could the HP provide a baseline heat for you that is supplemented by something else? These may have an impact on whether you are eligible for RHI payments and so on tho. Everything is possible, its harder to decide if its economically sensible.

 

[gangzoom]

We had a visit from an Air Source Heat Pump installation company recently. They said it was only worth pursuing if we could dramatically improve our insulation.

Surely if you improved insulation any existing heating system will work better too??

Electricity prices are rising compared to gas, given the same well insulated house whats the actual advantage of ASHP?

Our gas boiler will generate steaming hot water for a shower from a totally cold tank within 10 minutes, sounds like ASHP will need to run for hours to do the same?

My old Leaf had a heat pump.....to be frank it was next to useless, and when it got properly cold it drained the battery just as quickly as our X with resistance heater.

The difference been the X actually warms up inside, wearing a coat+hat was mandatory in the Leaf regardless of what temp I set the heating to.

 

[Talllbloke]

Electricity prices are rising compared to gas, given the same well insulated house whats the actual advantage of ASHP?

Well, to be blunt: burning gas will eventually kill us all whereas electricity from renewables won’t...!