we were considering geothermal but heard very bad reports from a plumber who installed it in his own place - very expensive on electricity and not that effective.
We decided to go with underfloor heating down stairs, wood pellet boiler to heat & 3 solar panels as well. Only at the stage of outting in windows now so cant tell you how its going but its meant to be great.
You get a grant as well for the wood pellet boiler & solar panels so it works out very cost effective
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