Pompe a chaleur - reduce your heating bills, at what cost?

Given that summer is here at last...I thought I'd take a look at the best ways of heating your house in France. Better late than never, and it might just help reduce the cost of fuel / oil next year - which I'd guess won't be any less than it is now. There are now several more environmentally friendly alternatives for heating a property, which may also be cheaper, though until now I've been unconvinced. In this post I talk about pompes a chaleur - heat pumps.

Pompe a chaleur

The pompe a chaleur (heat pump) is a system that extracts the energy in the air or soil and uses it to heat your home. The version of the pompe a chaleur - from now on referred to as a PAC - that uses the energy ever present in the soil is commonly called a geothermal system (discussed separately below). The PAC system can be linked to your existing central heating system to provide the hot water to heat your home, or can be used to heat air which is passed around your home.

That sounds ideal don't you think? Well, there are limitations. Although all air contains energy, the colder the air is the harder it becomes to extract the energy. And below a certain temperature it becomes more or less impossible.

The other downside is that the PAC requires electricity to operate it. The ratio between the electricity consumed and the heat produced is called the 'coefficient of performance' - clearly we would like this to be as high as possible, but in practice it is usually 3-4. That is, one unit of electricity produces 3-4 units of heat. Still, not too bad, albeit some way from the 'theoretical maximum' of 15.

Models on the market at the moment can typically produce up to about 20kw of heat. Not too bad, but not entirely sufficient for a larger or poorly insulated house, especially when we remember that efficiency falls with the temperature of the air outside.

There are no CO2 or other emissions or polluants, except those generated to create the electricity that drives the pump (often nuclear in France).

Because this system becomes limited at low temperatures (below about 5 c) it is necessary to have an alternative system in place as well. If the system is used to heat air in the property, rather than the water in a central heating system, a method for enabling the warm air to circulate around the building will also be needed.

This system of heating is popular in several European countries, notably Germany, France and Sweden. In some countries of northern Europe it is said that more than 90% of new-build houses have some form of pompe a chaleur system fitted.

Geothermal Heating

Using the same general principles as above, but geothermal heating pumps a liquid - usually a special liquid rather than simple water - through pipes buried a metre or so deep in the ground around the building. The pipes then 'gather the energy' from the soil, and the heat pump converts it into heating for your home. As above, your main cost (installation aside) will be the electricity to operate the system.

This system therefore has many of the advantages of the air-based system described above, while avoiding most of the disadvantages. The temperature in the ground is much more consistent - and higher in winter - than the temperature in the air. The primary disadvantage is that you need quite a large area of terrain next to your house that you don't mind being bulldozed - which may be complicated if you have a garden!

Installation costs also are of course much more for a buried geothermal system when compared with a simple air pump next to your property.

Both forms of pompe a chaleur heating described above - air heating and geothermal heating - will be more effective with an underfloor heating system than with radiators, because there is a limit to how warm they can heat the water in the central heating system. Radiators typically need water much hotter than a modern low temperature under floor heating system which, because of the large amount of pipes used, can use much cooler water. The floor in a modern underfloor heating system does not feel warm to the touch.

Of course, the costs of installing a new underfloor heating system in your property are much higher than retaining your existing system, since they involve completely excavating and renovating your floor, and it will be very disruptive if it is not a new-build property.

Although it's not very easy to understand 'at a glance', for detail of the costs involved in installing and running these systems see www.ademe.fr/particuliers/Fiches/pac/rub5.htm which looks at all types of PAC - geothermal, air to air and air to water heating, and compares the costs of the different systems. It will also prove useful as a refernce point if you are currently getting devis (quotes) for the work.

General issues

Some other considerations before you install your shiny new pompe a chaleur:

- The systems are often reversible. This enables you to heat a swimming pool, or air-condition your property in summer, by extracting warm air from the property.

- Installation. Some companies are 'better qualified' (or perhaps just more experienced) than others to install these systems of heating, and it will be difficult to separate the good from the bad. I don't have a great answer I'm afraid, unless you know someone who is very pleased with an installation. You could try those listed at www.afpac.org as a starting point (the Association Francaise pour les Pompes a Chaleur, believe it or not).

Cost versus performance.

This is the big question of course. The systems, especially geothermal, are not cheap to install. A geothermal system will cost a few thousand euros more than a conventional heating system.If you are planning to install this system in France be aware that there is a tax rebate of 50% of the cost of materials - ie the cost of the PAC but not the cost of the installation (there are certain limits on the amount of the rebate eg 8,000 euros for a married couple).

Rumours that the prices of PACs increased by the amount of the grant as soon as the grants were introduced might not be true...

The exact calculations depend on your situation: whether it is a new-build property, whether you are resident for tax in France, and lots of other factors that make it impossible to give a definite answer. For us three years ago the answer was definitely no, but fuel prices keep going up, and technology improves, which changes the balance.

Try and calculate - how many years you expect the system to last; installation costs compared with a conventional system; annual running and maintenance costs; savings you anticipate making etc and see if they work out. Then add in the feel good factor - knowing you are not destroying the planet, or paying for oil so often.

You are trying to work out - how much you need to pay out now (or how much extra, in the case of a new installation), and what will be the benefit in the years to come. Hopefully one part of the calculation will be much bigger than the other, and the answer obvious. And please let us know what you decided, and why.

As postscript: we personally now use a woodburner in conjunction with an oil-based central heating system - I suspect that using a woodburning stove in conjunction with geothermal heating would be the ideal solution, especially now that there seem to be lots of weeks when it would be nice to have 'a little bit of heating on' i.e. when the air temperature is about 15-18 centigrade, which would seem to be the ideal time for using a pompe a chaleur.

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  1. Jean June 19, 2008 at 8:18 am

    I’m interested in your post because we are in the process of gathering etudes on the PAC and the Geothermie – but the forage system. Unfortunately for us (well, in this case anyway) we are surrounded by a moat and the boiler is at the back of the house which means the access for the forage is not possible. This would otherwise have been idea. The PAC is a problem because the house is big and old (14th century manoir) and without insulation. However, as we are more than accustomed to living in 16 degrees that’s all we require from the system. If we can maintain that with a PAC, rather than fuel, then that’s what we will do. We have a PAC on the pool, installed in 2000, and it’s very good but, as you say, limited to 5 degrees outside temperature. However, I believe things have moved on and lower temperatures can still produce a reasonable heat exchange. We have calculated that in an average year we have two weeks when the temperature falls below -4 degrees and have therefore based our calculations on that. I should add though that we have the EGP electric system which is now no longer available, and this makes the system cheaper for us.
    At the moment the problem is finding which size PAC we need and I suspect that will be the deciding factor.
    Incidentally, we were told that any calculation should be based on the system paying for itself within 10 years – not more than.

    I have looked into another option (given that our house is ALWAYS cold to other people). I am looking at buying second hand fur coats off ebay to wear on those days when the house is just too cold even for us – and of course to lend to our guests who are used to 20 degree living. I’ve always maintained that fur for warmth is not the same as fur for vanity and I think in the depths of winter we qualify for the former!

  2. Boris June 20, 2008 at 5:13 am

    Jean, you don’t need to buy fur coats you need to start shooting rabbits and making coats for yourself. Even cheaper than ebay, and very elegant I’m sure.
    The ‘life of the system’ as 10 years is interesting since its crucial to evaluating the system – I guess that underground pipes are non-corroding and last more or less for ever (leaks at joints aside) but 10 years for something with moving parts – ie the PAC itself – sounds quite a long time.
    Is EGP the precursor to Tempo, where you have about 20 very expensive days in winter, about 40 mid-price days, and the rest of the year very cheap? We use tempo but I didn’t mention it above because it confuses the calculations even more.
    Likewise I didn’t mention the forage version because I believe it is less common – does it cost more than a ‘normal’ geothermal installation?

  3. kathy July 6, 2008 at 9:42 pm

    Have a cast iron black stove-says Chaleur 6-1-1982 any idea of the value. Want to sell
    Has two doors that close, to connect outside but in house, any help you can give me will be apprceciated. has serial nu,ber too
    Thank you

  4. Boris July 7, 2008 at 5:30 am

    If anyone has knowledge of the value of a second hand stove please post here. I can forward your details to kathy if required.

  5. Jean Halford-Thompson July 7, 2008 at 12:56 pm

    EGP is indeed pre-Tempo with the 22 ultra expensive days and the rest ultra cheap. No in between as with Tempo. EDF stopped it 10 years ago as it was so popular they were losing money!

    We could shoot rabbits and make the coats/eat the meat – or at least we could have done up to last year. We were over run with the little blighters who ate EVERYTHING out of the veggie plot. Now they seem to have settled down again in number and although I see one most days they are no longer such a problem. Back to ebay I fear!

    Forage is certainly more expensive but more efficient (so they say! I wouldn’t know). To be honest, we don’t have any aspirations of ever getting our room temperature above 17 degrees during the winter (and that’s on a warm day!). We just want to know that we don’t have to mortgage the house to achieve that 17 degrees. We are not complaining about the cold – after all we chose to live in this beautiful old house – just searching for ways to stop our teeth chattering so that we could complain if we wanted to!

  6. Johnny Norfolk June 28, 2009 at 7:27 am

    Every time I have looked at things like this. The cost saving return period is just far to long. So I have let my head rule my heart and nevr gone down this road. I have yet to find any of these syatems when their claimed pay back periods are correct.

    I must say I am finding your posts very interesting. Its so good to read so many interesting pieces. Mrs N is not at all happy that I have found your site as I am spending ( in her opinion) far to much time on the PC dreaming about France.

  7. Boris June 28, 2009 at 8:11 am

    Interestingly our friends did a lot of research a year ago and decided the same – but they have just come across a new pompe a chaleur system that claims to be much more efficient and much more cost effective. It is also very large (1 cubic metre?) and heavy.
    I remain very sceptical, mostly regarding efficiency and electricity bills when the temperature drops below a few degrees – but they say it is more convincing than the ones that were around a year ago. I’m looking forward to hearing how it works for them.

  8. Chris Skerry October 18, 2009 at 6:48 pm

    I am investigating a PAC with two 100 meter bore holes. The potential installer is http://www.geothermic.fr in the Vendée (D=85). Does anyone know if they are any good? They make the PAC and also own the company that drills the holes.

    In my studies on heat pumps, I have come across a website that says that EDF will still give a Tempo tariff. They wont be keen, but can be persuaded. I pay about 4 centimes per kw/h (on a blue day – the cheapest) in France, and 12.5 pence all the time in the UK. It seems that running out of coal was good for France.

  9. laurence September 13, 2010 at 6:39 am

    We have studied the pros and cons of heat pumps ( pacs ) and geothermal . The problem with pacs is that they become less efficient, i.e. give out less heat or less cold air, as the external temperature gets colder or hotter respectively. To the point where at an external temperature minus 15° the pac gives no heat whatsoever. So the more you need heat the less it gives you. Therefore you have to have a back-up heating system which rather defeats the object. As to ground source/geothermal , the main drawback is that it can only ever give about 12° of heating when most people want 20°. Its best use is as underfloor heating in a small new-build , well insulated. The system we looked at needed 12kw of dedicated 3 phase electricity , when the heatpump kicked in. That is total electricity supply to the average house. As to grants, it seems that the grants are only paid to cover the labour cost, and then only to registered French installers. The labour cost is in direction proportion to the amount of the grant. There are a couple of other gadgets that should be viewed with scepticism, for example the pac pre-boiler, that is connected to the central heating circuit. It will never never repay its cost.

  10. Chris Skerry September 21, 2010 at 10:40 pm

    It is now September 2010 and my system is just installed. I am pleased with it, but can’t tell you how good it is because the heating season has not yet started.

    If you are interested look at http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=6164

  11. Boris September 22, 2010 at 5:04 am

    Hi Chris, that’s good to hear and thanks for the link giving your story, lots of useful information to think about. In a few months it’ll be interesting to hear how efficiently it works when it gets cold. I like the idea of using Swedish technology.
    The pdf document showing the results of an extended heat pump trial referred to is also interesting – download from here. Shows that they can work, but correct installation and use are important to get satisfactory results, among other things.
    But I noticed it said that (in the UK) the payback period compared with a new fuel based installation is 29 years. A long time, probably longer that the life of the heat pump I imagine. So if the system costs more in France (probable) it is likely not to be efficient in terms of cost savings, although almost always efficient at reducing carbon emissions, the reports primary concern.
    Also ‘if a heat pump is installed even slightly wrong, the outcome for the customer may be very wrong’ – correct installation is critically important.
    Cheers again.

  12. Chris Skerry September 22, 2010 at 8:00 pm

    Boris, Thanks for your kind words. It seems that installing a heat pump can be a very risky financial activity. I am fairly confident that mine has been installed correctly, but I am not at all confident that the huge variety of parameters are set up correctly.

    When the heating season starts, I will try as hard as I can to ensure the parameters are set correctly. With underfloor heating which has a huge thermal mass and is very slow to react, I should be able to have long ‘on-cycles’ which I believe are the most efficient for a heat pump.

    There is no way I will live long enough to get my money back. I have done it because it is a project I find very interesting. Perhaps the next owner will reap the benefits.

    We shall see. . . . . .

  13. Chris Skerry March 20, 2011 at 9:57 am

    The pump is now installed and working. There were a large number of initial problems to be sorted out. I think it is now almost correct – just a few tweaks to go. The system works well and as the heat pump efficiency is theoretically 4.25, when I put in 1 Kw, I get 4.25 Kw out.