We've been told by lots of people that ground source heat pumps can be highly inefficient, in order for it to be effective the system has to be designed very well.
This is true for heat pumps that have not been properly configured, but otherwise heat pumps are very energy efficient. For every unit of power you put into the system, the system delivers 4.5 units of heat. But as said, it's very important that the system is fine tuned to your house, and that the heat pump is tailored to your house with regards to capacity (obviously not too little, but also not too big). All this is true with regards to your ventilation system also.
The key to our house is insulation, walls, floor, ceiling all super insulated, all windows triple glazed.
Agreed. Insulation is like covering your house with a blanket.
There are a few of threads about it at
www.aecb.net (you should join, a very useful organisation).
Very useful! Thanks for the tip!