I plan to purchase a carrier furnace the square footage of my home is 1,325 sq. ft. What size furnace should i purchase and can i use the existing flume which exhausted gases for my old gravity heat system the home was built in 1946.
Also what is the formula for determining the BTU's for 1,325 sq. ft home with the 2 longest runs
being approx. 25 ft and the shortest runs 10 to 15 ft. for a single story building