Tim Bradley says heat pumps are used extensively where he lives and wonders why they are so expensive in the UK

Re your article on heat pumps in the UK (Are heat pumps the future or just a lot of hot air? 28 September), I live in the middle of Sweden, about the same latitude as the north of Scotland. Nearly all the houses in my area have air source heat pumps.

When the air temperature is about 7C, these pumps give energy efficiency of between 400% and 600%. A seasonal coefficient of performance of 3.5 to 5 is the norm here.