Rolf,
first I would think about proper thermal insulation. No point in heating the back yard too. Second I would use water as a transport medium. Natural gas burners are very good, if you have a gas pipe near you. A gas burning powerplant can provide all the hot water and heating you need for your home. The unit is very small - aprox. 45x60x90 cm, you will need to use radiators in all the rooms. But ... is there a natural gas network there ?