Answering your question: Upper right-hand of the glass doors are two heat exchangers, one is gas forced air and the other is heat sourced from our outdoor wood burning furnace that super heats water, (hot water passing over a plenum and fan blows heated air). My studio is 800sq.ft and is the second story over a two story garage built to look like a grain elevator. We live in a restored Victorian in rural Wisconsin. This week we are double digits below zero.