Heat pumps: a history

sir – Having had a ground source heat pump at work in our Victorian-era house for some 15 years, I remain astonished at the level of ignorance about these excellent devices.

It was demonstrated by the Business and Energy Secretary, Kwasi Kwarteng, with his claim that heat pumps “are still in their infancy” (Interview, August 22). In fact, they have been in Swedish homes since the 1970s. The technologically innovative company Robert Bosch has specialised in manufacturing them for many years. Stephen Hazell-smith

Penshurst, Kent