I have a zero clearance firebox that is approximately 25 years old. Previous owners installed it and only burned wood. I'm looking to supplement my worthless heat pump when temps are below 32. First chimney sweep said a zc box that old wasn't made to shelter the heat from a wood burning insert and recommended the Hearthstone Homestead stove model. My house is 1600 sq feet and this stove claims it can handle up to 1800 sq feet. Second chimney sweep said either would be fine regardless of the age of the zc box and said an insert would throw more heat. First fireplace shop I went to was very pro Lopi...more btus, better at heating a house. They didn't seem too concerned over the age of the firebox. They also said I would have to buy something that would heat at least 2,000 sq feet to adequately heat 1600 sq ft. Second fireplace shop I went to was very pro soapstone...gentle heat, longer burn times. Since more heat is put out into the room and not against the firebox, the age of the firebox was not a question. I know the efficiency of either is best of burned 24/7, but realistically, I'm only going to burn at night. How much should the age/condition of the the zc firebox weigh into my decision? How long should they last? At 25 years old, is it past its life expectancy?