How do we know what size furnace we need and/or if we are being oversold? We live in western Oregon so have a fairly mild climate. Our house is 1950sf, one level, built in 1983, with the original 80,000 btu Borg-Warner furnace. We have vaulted ceilings in the combined family room/kitchen area. We have updated with vinyl, low-e windows with argon; added floor insulation (R21); wrapped furnace ducts; replaced doors with energy efficient doors; and have original R-11 walls and R-30 ceiling. It has been recommended that we should have a 90%, 2-stage furnace with variable speed blower. Two contractors recommend a furnace with a BTU output capacity of 74,000; another recommends 56,000. We need help sorting this out.