Hi fellas, I would like to make use of your collected experience like many others to answer some questions. I have a 1500 sqft main floor and a 600 sqft 2nd floor with an open fireplace in my greatroom. I have attached a pretty approximate drawing of the first floor. The main obstacle on this job is my foreman, she has very strict requirments on fit and appearance namely a flush finish and whatever fancies her at any given moment. Anyways this has severely limited my options as I would also like to qualify for the tax rebate on efficiency. At this point my main goal would be to heat the great room and possibly the dining room and kitchen. I currently have a mono flow boiler system with adjustment on each register. If I was able to heat this area I would be able to close off about 60-80 feet of register which would be over half of my registers. My firebox is 36w at the front 27 at the rear, 30H and 22D. Because of this I am looking at the Osburn 1900. My biggest concern is that the 1.2 cubic firebox and proposed 45,000 btu wont be adequate for the job. Osburn states that this insert will heat up to 1200 sqft but I do not want to end up in a situation where I am grossly undersized. Any and all advice is appreciated.