Heat Recovery Unit. This is a very novel system in the UK, and the idea is to recover heat from drain water before it escapes the building. Averil has been asked to take quite a lot of measurements to see how good it is! More details can be found at: www.renewability.com

Averil adds in May 2008:
"The heat recovery unit will probably go. It was designed for use within the house, not outside, so it is not applicable for many typical English houses. Also my solar panels produce more hot water than needed for much of the year so its contribution is redundant."