How does a heat pump work?

We get a lot of questions on this, so here's the answer. A heat pump does more or less what it says on the tin: it pumps energy from one place (usually outside) to another (usually inside). It turns out that you don't need to work very hard to move large amounts of energy around in this way, so heat pumps are quite efficient. 

The other thing people ask is how you can heat a home to 18 or 20 degress when the heat source, in the air or ground outside, say, is only 4 or 5 degrees. Perhaps the easiest way to think about that is just that the heat pump is also an energy concentrator of sorts - it is harvesting energy from a lot of air (or ground) and using it to warm up smaller amounts of air (or water) in your house.

What's perhaps most interesting about this is the source - How Things Work - The Universal Encyclopedia of Machines - first published in 1967. A reminder that we have been around the energy-saving block at least once before, so far (it has to be said) with no success. Have another look at this year's Godkin lecture by John Deutch of MIT for a first hand account of how frustrating that is for people who were involved in this sector in the 1970s.

Open publication - Free publishing - More refridgerator

PS I am not sure who has the copyright to these pages. I have looked for the original publisher online (Granada) but they are long gone, it is now 40 years since this book was published. There is a US website called How Stuff Works that has a useful (and somewhat more modern) page on heat pumps.

PPS heat pumps are not the best solution for many houses. The typical savings are often not better than a Band A condensing boiler running on mains gas, and the performance (in terms of comfort levels) can be poor, especially in large uninsulated homes with radiator-based central heating.