Hi OP, we have the Carraig Mor 30KW with back boiler in a new build. Our house is airtight as we have a heat recovery system and I have to say, the heat out from this is just unreal. We have oil back-up but havent used it in 9 months. Heats 18 radiators and is extremely fuel effecient. We have a Boru room heater stove, a Carraig Beag, in the dining room (we have big open fireplaces in both rooms) and its perfect. cant believe the difference the airwash system makes to the glass, but the fuel efficiency is what does it for us. We bought both of ours in Carrick-on-Shannon , and found them very good to deal with.