I know this is an old post, but how come no one really made any comments about the previous fuel usage in this space? If they used $1500 of LPG for heat, probably using an unvented heater, then they were losing a lot of heat. It doesn't seem possible to burn that much LPG with a single wall heater in one season. If they doubled their electric bill with a one-ton window unit AC, then they are gaining a tremendous amount of heat in the summer. This electric usage also seems impossible, unless they have a VERY small "normal" electric bill for their home. Why will this install pay them back anything really, unless they tighten the space up?