How big a house will a 75000 btu furnace heat?

Heat load calculations need to be conducted for home to determine the proper size furnace. There is no simple answer to this question. There are a number of factors that can effect what size your furnace should be. Example: square footage, duct work size, insulation factors, Windows etc. I recommend having a heating professional look at your home and conduct a heat load calculation. Over sized and under sized furnaces can cause you number out problems in the long run.