I would tend to agree with the 96% suggestion. At one point a fee years ago there was talk about banning the sale of 80%ers in the northern states. The only way I wouldn't do a high efficiency is it the vent was not possible to run or you get an 80% for dirt cheap. Ie: got my Trane 80,000 BTU 2 stage 4ton drive for 200$ just has a dent in the door from a hand cart.