I want to add a fireplace to our family room that is capable of burning wood and propane. My desire is to have a propane fired unit that could be converted to a wood burning unit if for some reason we were unable to get propane (natural disaster, etc.). Would it need to be zero clearance, and on an outside wall. Room is only 15' x 15' with 8' ceilings, so probably we would only need a medium (36"?) sized unit. Also, the fireplace would be used as a supplemental heat source so efficiency is a consideration. What makes and models are available?