I have a house that's 26 years old and I believe that the A/C and furance are both original and installed by the builder. The A/C has crapped out. Given the age of the furnance and, what I assume have been improvements in technology and engineering over the last quarter century, I might as well replace the furnace now, as well since I'll probably see good returns in both energy savings, comfort, and improved marketability of my home in the unlikely event that I sell in the next couple of years. I've had two contractors out to offer bids so far. The first contractor pushed an 80/20 two-stage trane unit for the furnace saying something to the effect that it'd be difficult to install a 92% efficiency furnace because it'd be difficult to run the extra venting. The other contractor disagreed with that assessment saying that it would be no problem at all and he pushed a York Affinity system (which he claimed was a 65-stage, 95% efficiency furnace). Naturally, alarm bells are going off in my head when I get this type of conflicting assessment from professional contractors. I've been googling the hell out of York, Trane, "furnace reviews", et al. What I've found, so far (and this was validated by consumerreports.org) is that the selection of a good contractor is more important than the brand (although Goodman was not looked at favorably time and time again). I've read that a low-end furnace installed properly is better than a high-end furnace sized or installed improperly. So I'm looking for some advice. First, what do you think about the two contractors and the their conflicting views on the issue of a high-efficiency furnace and the venting? Second, what's the general consensus on York Affinity series (1% increments between 35% and 100% which, I assume, is why he called it a "65-stage")? Third, I've seen mention of Manual J HVAC Load Calculations all over the place. Neither of the contractors showed me any calculations that they did to come to their conclusion on the sizing of the furnace and A/C. Should I ask for this? Is it an indication that I'm dealing with a poor quality contactor if they don't do this? Sorry for the novel, here, but I'm eagar to learn as much as I can so that I have the best experience possible.