Had one fitted in my husband's house in France. I think the major thing is insulate, insulate, insulate. If you fit one in an old property with no insulation on the walls, internal or external, as well as loft insulation, then you will have large electricity bills. It is the way we are going, and they are efficient; one unit of electricity in, gives you two out. You can also fit them onto an existing gas central heating system - which is great. In France you get good grants to buy and install - don't know what the situation here is, but suspect it won't be as generous. If your home isn't highly insulated, I would spend the money on that, but if it is I would do it.