I'm considering what type of heat pump (air-to-water or ground-to-water) to install for a house in hilly terrain in Central Germany, to replace an old oil heater from the 1990s. The house has a 750 m² plot with a backyard of around 19 m × 15 m, so horizontal ground collectors might be an interesting option. But: the house is built on a slope of around 30% (the backyard slopes 5 m up over a length of 15 m, and the highest point of the plot is around 13 m above the lowest), which is not horizontal. Are horizontal ground collectors possible to be build on such a slope, or do they need level terrain? A German language forum thread on the topic is inconclusive. The topic of slopes is not discussed on this thermalearth.co.uk page.

A borehole is uneconomical for the property because the house is built on a hill, so the hole would have to be much deeper than in other areas.

  • $\begingroup$ This question might be better answered on SE Engineering. My initial thoughts are that having a sloping trench for the buried pipes shouldn't be a problem, but a variable depth trench with a horizontal bottom may be a solution. There would be three ways to have trenches for such a system. Trenches dug up hill, either uniform depth with a sloping bottom or variable depth with a horizontal bottom. The third arrangement is have the trenches dug across the hill, mimicking an elevation contour, but having a series of horizontal bottoms in a stepped arrangement going up hill. $\endgroup$
    – Fred
    Commented Jul 27, 2023 at 10:12


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