Air source heat pumps

Anyone installed these and how effective are they?

We have one which had been fitted by the previous owner. It works but it is not without issues.

One thing to consider is the low temperature performance, the heat pump in our system is a Stiebel WP13, these units work best in a relatively mild climate - there is a noticeable fall off in output below 5°C so just when you want heat out of it, it becomes less effective.

If you are replacing a conventional boiler in an existing central heating system you will need to consider whether to replace the radiators. Heat pump systems run at significantly lower flow temperatures than boilers, typically 50°C compared with 80°C - this means that modern, high surface area radiators are best suited. Our system has fairly old radiators and they are manifestly lukewarm - the system does get the house quite cosy but it takes about 24 hours to do so from a cold start. In fact 50°C is something of a compromise - the WP13 is specified for flows up to 60°C but it is very inefficient if you do that with a maximum CoP of only just over 3 (i.e you need to put 1kW of electric power in to get 3kW of heat out). It really wants to run at a flow temp of 35°C when it is capable of a CoP of over 4.5 but that flow is too cool to do anything much with (EDIT: It’s probably good for underfloor heating).

Another issue with cold weather is that you have a large box full of water pipes outside exposed to the frost - in a second home this might be an issue. The last time we went over I discovered that, despite being left on “frost protect” the system had run into a problem and was not working so it had been off for two weeks. Not just any two weeks but probably the coldest period in Jan, temperatures of -8°C for several nights. I nearly had kittens when I noticed that the pressure gauge on the water circuit was down from 2bar to 1bar. Thankfully there were no burst pipes as far as I could tell - the outside heat exchanger is well lagged - but if you are not prepared to drain the system you might need to leave it on during the coldest months, even if not in the property (I elected to do the latter, back in a week and a half to see how well that went).

They need a fairly beefy electricity supply - we had it increased to 12kW when we bought on general principles but the chap that had the system installed only had 6kW and, apparently, the system would often cause the main breaker to trip. On 12kW, so far, there have been no problems.

They aren’t all that DIY friendly - although this depends on how DIY savvy you are in the first place.

Ground sourced pumps avoid some of these issues but are more expensive to install, and need room to bury the heat source pipework. However there is more scope to install the heat pump inside, especially if you have a basement, where frost might not be so much of an issue.

Whereabouts in France are you?

Hi thanks for that. We are in Finistere. We currently have a gas boiler which runs off gas bottles to heat normal radiators so we have the infrastructure (radiators) but gas bottles and finding someone to service gas boiler in NW France unheard of.

Was thinking of air to water so as to heat the radiators. Someone is here all year round.

OK, so at least you are in a part of France with mild winters on average. We’re a bit further south in the Morbihan.

Gas central heating using bottled gas rather than a decent sized tank in the garden must be a total pain!

EDIT: It might not be much better getting engineers to sort a heat pump - it was like pulling teeth when I tried to get the original fitter to get someone out to look at a fault last year and I haven’t been able to get a quote from him for some minor work to modify the system (so I’ll be doing that myself), nor is he slightly interested in thinking about whether the start-up current from the compressor (which still dims the lights even though the breaker no longer trips) represents a fault or “just one of those things”.

I am interested to know what people’s views now are on air source heat pumps.

I am considering installing one in one of our houses in the middle of a village - and also a geosource heat pump in our separate house that has a large garden.

Absolute rip-off, even with any potential tax ‘incentives / rebates’. They literally eat electricity (many require 3 phase supplies just to start them up!) and are bloody useless in the winter if the outside temp drops below zero (i.e. resistance heating only - no ambient heat). Better off with twigs and a piece of flint! :wink:

Electric underfloor heating / wood burner combo is the way to go…

I have been investigating and would agree with Simon’s assessment… they definitely need a back-up system in low temperatures… ie Winter…

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ie when you need the heat !!! Ridiculous system…

Is there anyone on here who has one?

Yes me !?! (Ciat system)

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Do you have a new or an old system and have they progressed over time?

Is electric underfloor heating expensive to buy and run. I’d love a warm salon occasionally.

Mine (Ciat) is 12 years old and I’ve no idea if they’ve progressed over time - although I guess the heat exchange concept is the same - i.e. you’ve got to have heat to create heat cheaply. Can be an ‘issue’ in the winter - funnily enough :wink: Cost 20€k to install, got a lovely 5€k tax rebate/incentive and spent it on the leccy bills. Now got electric floor heating which costs a fraction to install / run v heat pump - no brainer. Heat pump currently rotting…

PS also got some great retro-fit ‘under-rug’ electric heat mats which are bloody brilliant.

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Dutch friends put underfloor in their kitchen/diner 2 years ago. They’v e been disappointed. It does add a very gentle something for bare feet, but they still need a good heater to keep the room comfortably warm.

I wonder if that was electric or piped-water UFH Stella. In my experience, the piped-water systems can be pretty crappy as they reply on external heat pumps to warm the water!!!

I honestly think heat pump were developed as a plot between the manufacturers and the leccy companies to milk consumers dry!

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I think it is electric… I’m trying to recall how it looked at the various building stages… There is no boiler and it would have been a good topic for discussion if they had mentioned a heat-pump or similar.

They’ve since put in a cast iron wood burner… which takes huge logs … and throws out lots of heat.

Incidentally, they put in the most amazing (to me) level of insulation in the property… so what heat is produced, stays where it is meant to be…

I think that Insulation is top priority… whatever the heating system…

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Heat pumps are suited for new build, well designed and insulated properties - water underfloor heating works at the lower temperatures and is therefore ideal for heat pump applications. I have experienced UFH in two properties in the UK, one was a modern well insulated house and was economical and lovely to live with , the second was a converted victorian villa and it was cold and not sufficient. I would have it in a new house, not in a conversion of old property.

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Fair comment Peter… useful to have input from someone with personal experience.

I do have one query… UK temperatures are nothing like those we experience in France… are you sure the system you had in UK would work as well here at the winter temps we get… way down in the minuses…

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What do I look for in France for under rug heating mat please?

Teresa - I got them sent over from the UK.

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