Well, I'll put it this way: 1. drilling deeper than 99m is not allowed here! Only 1*99m might be possibly too little. Better to go straight for 2*99m. 2. there is still a back house here. If that is once insulated and renovated, maybe the 145sqm can still be connected to the heating?! I don't know how easy it is to run insulated heating pipes about 30m distance. The heating system itself can handle that easily and fortunately the drillings are deep enough.