Air source heat pumps

I should be clear my experience is limited to running the system in the French house, plus what I have gleaned online. The claims can be checked with a bit of analysis though.

Most of the video was marketing speak but I did spot a couple of claims.

The first was the rebate stuff which was UK specific and, to be honest, I have no idea how accurate that was.

Then there was (I think) 40% less CO2 emissions than gas - this page gives some comparison figures for CO2 emissions per kWh for various fuels.

Electricity (UK) - 0.527kg CO2 per kWh compared with 0.185 kg / kWh for natural gas and 0.245 kg per kWh for heating oil.

So, to be 40% better than natural gas you need to get down to 0.185 x 0.6 - 0.111kg per kWh. That needs a COP of 4.74 or better - uncannily almost exactly the figure they claimed in the video so that, on the face of it, stacks up.

But wait a moment gimoozaabi - the installation manual for their 8, 12 and 16kW units tells a slightly different story.

The performance data is on page 44, in the form of a table with vastly fewer data points than the Stiebel unit but what is there is sufficient

A8M A12M A16M
A7W35 6.3 / 4.42 12.3 / 4.72 12.3 / 4.72
A7W55 6.2 / 3.1 12.5 / 3.2 12.5 / 3.2
A7W65 6.3 / 2.7 12.4 / 2.6 12.4 / 2.6
A-2W35 6.7 / 2.9 12.0 / 3.3 15.5 / 3.2
A-2W55 7.1 / 2.1 12.0 / 2.5 15.6 / 2.4
A-7W35 7.0 / 2.9 12.0 / 3.0 13.2 / 3.0
A-7W55 7.1 / 2.1 12.0 / 2.2 15.3 / 2.2

A7W35 means intake air 7° with a water flow at 35° and the figures are heat output/COP.

The claim that heat output is maintained down to an air temp of -7°C seems to hold, more-or-less but the COP drops way down to just 2.2 worst case for the 16kW unit so you aren’t going to be saving the planet 40% CO2 compared with gas. They give a “seasonally adjusted” COP of 3.6 which is hard to check but is a bit more realistic than 4.7 - at that level you would still be ahead on CO2 but only by a shade over 20%.

I note they are fairly candid that the system works best with lower flow temperatures and is not well suited to conventional radiators.

So, in conclusion I think their CO2 claim is “optimistic” rather than actually mendacious.

However while I’m happy to feel all warm and cuddly saving the planet I would like to know whether I’m saving myself money - the UK average electricity price is, apparently, 16.3p per kWh and that of gas 4.2p - a factor of 3.88 - given that seasonally adjusted COP of 3.6 it suggests that a heat pump would actually be more  expensive than gas heating in the UK - I guess that’s why they are pushing the environmental aspect :slight_smile:

Obviously the economics will differ slightly in France and, overall, their 16kW unit looks to have slightly better performance than my WPL16S - but not radically better.


Thanks for the detailed reply.

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LOL left me feeling decidedly thick - thank goodness for electric underfloor heating!

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Nope… I almost see what you mean… but not quite… I prefer to throw the windows open and let the fresh air in…

and… bathrooms… the fresh air comes in and the steamy air goes out… and it’s free, no electricity… only takes 5/10 mins and it’s all demisted…

But… that is me… and, as we all know… we are all very different in the way we see and do things… :wink:

Not just in France Stella - UK too. It is part of the Building Regulations.

New-build homes are so effectively air-tight these days that the Regulators have had to enforce a minimum number and volume of air-changes per hour to prevent the build-up of stale air. Yes, you can open a window to achieve this but , pound to a penny, that wont happen in the dead of winter. So, regulate the builder to install mechanical ventilation. It costs the builder to fit them, it costs the house purchaser as the cost makes up a part of the house price and…they will get turned off for good by the householder because they use electricity and make a noise. Waste of time…

As for air source heat pumps, we sometimes fit them on our retirement developments if the site is too small to install ground source systems. We prefer ground source as there is no disturbance to neighbours, no unsightly mechanical monoliths and the GS system gives a better heat-flow in the winter.

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I used to chuckle at the bedding hanging out of the windows summer and winter alike… now I have “joined the club”… :grinning::grinning:

And there’s me thinking that hanging the bedding out of the window was boasting to the neighbours about the previous nights bedroom "activities":wink::joy::joy:

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Well they say for the healthiest bedding the bed should never be made. I usually strip ours back for an hour, windows wide open .

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I never used to throw bedding out the window until I had a conversation with an elderly neighbour aka the village gossip. She was talking about other neighbours and saying with a tone of disgust that she’d never seem their windows open or their bedding outside. Needless to say I now do so regularly.

They barely make a wispa installed properly and about £30 per year from memory. I used to explain to residents, the reason for their mold problem was they had turned them off.

Neighbours have remarked that there is often a lot of laughter coming from our house… at our age… things can get a bit comical… :upside_down_face::wink::rofl::rofl::rofl:

Thanks Paul - very interesting - however here in Brittany temperatures anywhere near -7 are virtually unheard of (I think only one night in the 7 winters we’ve been here) - the winter night average minimum is 5 degrees, and daytime average even in the middle of winter is about 10 degrees - so airsource makes much more sense for us (I’m only using it currently to heat the pool - which is great as it’s only used when the air temperature is comparatively high - but am considering an air-to-air unit for the house, which we currently heat entirely with wood, specifically for those not-really-that-cold days in Spring and Autumn when we don’t want to bother with lighting the fire).

Yes, our place is n Brittany as well - but there was a cold snap in early Feb a couple of years ago where the daytime temp didn’t get above freezing for about a week and the coldest nights were below -10 - we arrived in the middle of it to find the system shut down displaying a fault which basically said “water too cold to run pump”,

I had a nervous few hours after resetting and restarting the system, more than half expecting a split water pipe in the outside unit.


Thought of you just now, as I opened the kitchen window, rather than switch on the cooker extractor hood… :wink:

There’s not a great deal of steam and fresh air via the window… is free… (saving money to spend on wine… hic)

Yes the winter before last was the exception I mentioned - not as cold here as for you, but the pipes in one of our gites froze - but this was the first time in over 20 years to our knowledge, so I’m not really expecting such extreme weather again in my lifetime!

The mild Breton winters were one factor in realising that the previous owner’s installation was more reasonable than I initially thought.

Consideration of the alternatives was another.

But what really changed my mind was installation of a room thermostat.

The system had been installed without one - my initial thought was a bit “WTF” but reading the various installation manuals I realised that the system did not (technically) need one - during installation the rate of cooling could be programmed in to yield a “curve” which allowed the system to maintain a set internal temperature based solely on the outside temperature.

Except it never really worked well - in fact I found a copy of a letter from the previous owner to the installer complaining about the system’s erratic behaviour - which didn’t seem much better when I inherited it.

It took a while, my initial request for a devis from the original installer fell on deaf ears so I decided to do the job myself - except that finding a supplier for the now-obsolete controller proved tricky (eventually found a German supplier with them in stock) and it was a little more time before the project wound its way to the top of the to-do list.

But the difference was noticeable - from a system which seemed to heat (or more often not) when it felt like it to one where if the house is too cold I can turn a dial and it reliably gets warmer :slight_smile:

So, I have mellowed regarding air source pumps but still wish it had been ground source.



Ground source is more expensive, but if we have to move I am not sure that we afford to do it a second time.
I will show your remarks to Jim, but we are in Southern Burgundy, which can be colder.

Buy a boring machine, seems to be good money in that.

The current thread on boilers made me return to this one as I wanted to reference some of the graphs.

Re-reading my comment regarding the economics having looked at the price of from Primagaz of 10-14 cents a kWh and it is clear my hunch about it being different in France was more-or-less correct, looks like a heat pump compares very favourably to Primagaz - how much is mains gas per kWh in France?