Very early on in our project we decided to use a ground source heat pump to heat the house. These are clever devices that use a heat pump (reverse of a fridge) to raise the temperature of a coolant (in this case a water glycol mix) and have been used for many years in Scandinavian countries. As our house is part of a farm there is no shortage of space to dig a 1 metre deep trench about 150 metres long into which we put the ground collector (posh name for some 38mm plastic pipe). You can have a straight out and back loop, or a coiled loop (slinky) if space is at a premium, or even panels of piping (like a radiator in the ground) or even bore down vertically into the ground. Oddly, going deeper than 1 metre does not give you higher temperatures but does cost more to do so loops are the most cost effective route to go if you can.
While this output is slightly lower than ideal for a radiator system, it is ideal for an underfloor heating system.
Our heat pump suppliers had 8 employees when we met them in 2006 but so great has been the growth of demand they now have 80 staff just 2 years later!
If you would like advice on installing a heat pump and have any particular questions about the many claims of heat pump suppliers and the costs, send your question via a comment on an appropriate blog entry.