The Achill multi fuel Insert boiler is capable of heating up to 9/10 single radiators on the 17.1kw and 13/14 single radiators on the 21kw. It is primarily designed to heat water to radiators. The heat output can vary from 2 to 5.1kW heat output to room depending on how many radiators are installed in the building. We would strongly recommend that a radiator is fitted in the room where the stove is installed, to maximize heat output to the area