Our situation is an 1830’s stone-built house with reasonably good insulation (in the circumstances). The total estimated area of the building is around 550²m. Our existing oil boiler is a Kidd High Efficiency Condensing Boiler model #2 with an output of 160,000 BTUs/hr (47kW), which handles both hot water & heating. Total oil consumed is around 6,000 litres p.a. averaged over the past 3 years (but this includes an oil fired Aga).

Our thinking is to retain the existing oil boiler, as a backup and to kick-in during especially cold periods, but to otherwise rely on the ground source system for all normal heating & hot water requirements. We have based the calculations on John Cantor’s helpful hints at www.heatpumps.co.uk/viability.htm.

Luckily we have a field available close to the house where we can install the ground loop, so a horizontal (as opposed to vertical borehole) system seems most viable. We generate our own (grid-tied) electricity with a windmill producing 16,000 – 18,000 kWh p.a., so in a fortunate position for electricity supply.

The ground source installation set-up we are considering is:

• A cleared area of around 620² m. to a depth of 1.2m. (i.e. one big hole rather than a line of trenches, as we think this may be easier to work with and to backfill);

• 10 x 100m ground probes (slinky system) & 10 way manifold;

• A Stiebel Eltron WPF20 20kW system, installed as 2 x 10kW modular heat pumps including internal & external temp sensors;

• 1 x 400 litre buffer tank SBB400E and a 300 litre hot water tank.

I would appreciate views from anyone with experience of ground source, as to whether our proposed system seems sensible? In particular, are slinky’s ok, or more prone to failure than alternatives; and does anyone have good or bad experience of Stiebel?

Thanks for any advice.

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Peter