We have a 1860 solid stone cottage, approx 50m2 ground floor and same on 1st. looking to convert to attic for extra space. The Oil boiler was installed 2 years ago, with some new rads, double glazing throughout. no gas supply and we are installing a wood burner for some extra sitting rooms cosyness.

we plan to remove the oil boiler and replace with renewables. I like the idea of ground source heat pumps (GSHP) and Solar thermal panels, even the newer PVT panels for combined electrical generation.

Our builder commented that a friend of his had problems with GSHP in the winter when the temp dropped and i am concerned that such a system would not cope in the harsh weather with little sunlight.

are there systems or installations which overcome this issue and how ?


  • Samuel Joy

    Hi Stuart,

    These two articles should be of good use


    I don’t think it’s just potential low temperatures that should be of concern in your situation, as ground source heat pumps are generally better suited to underfloor heating (or low flow temperature radiators), but not normal radiators.

    Hope this all helps,

  • Keith Rule

    HI Stuart.
    I have been involved with heat pumps for many years, and we sell them. Our choice should tell you all. First, Ground source heat pumps like any should be sized correctly for output demand, with the correct nuber of ground collectors. However, you could acheive the same result using air source units. The MOST important things you need to consider in your design are.
    1. Max flow temp, i.e 65c, as heat pumps reduce by approx. 10c BELOW zero c
    2. Minimum flow temp, you will need at least 55c, and aluminium radiators designed to work at 50c to ensure you are warm enough. Otherwise you need to oversize your existing radiators by a large margin. Sorry you have recently purchased some, but if they are not suitable, then they are not suitable.
    3. CoP, get the best/highest below zero c temp.
    4. Ensure the heat pump runs through a thermal store, or buffer tank, any thing else will not work correctly.
    Something to consider. A ground source heat pump for a 14 kw output will cost approx, £2,500 per kw to install, i.e. £35,000. The same with an air source system will cost approx £10,000 installed, and give the same result if chosen and sized correctly.

    For more help you can e mail or see our site at http://www.kra-technical.com for more information and free guides to heat pump systems and how to size, design them.

    Hope this helps.

  • Tim Pullen

    With respect I think you are asking the wrong question. The first question for a stone cottage needs to be what technology will work best. It is possible, probable even, that neither GSHP nor PVT will work well. That is nothing to do with the efficacy of the technology, but to do with the demands of the house.

    My advice would be to calculate how much heat the house will need when the conversion is complete and then decide which is the most cost effective way of meeting that demand.

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