How do you pick a heating company when the quotes are all over the place?

The guy who did the load calculation is the only one of the three doing real work. A proper Manual J calc takes measurements of the house, checks window counts, insulation, orientation, all of it. Takes an hour or more. That alone doesn't gaurantee he's honest, but the other two quotes are basically guesses with a price attached. Wide price spreads for 'the same size unit' ussually mean they're quoting different install scopes, one includes things like a new thermostat, condensate setup, permits, disposal, and another is just dropping the box in. Ask each of them for the exact model numbers and a line item breakdown of what's included. That's where the thousands disappear into, not the furnace itself. The returns comment is worth taking seriously too. Undersized or too few returns is super common in older houses and no amount of new furnace fixes it. You can verify it yourself a little. Notice if some rooms are always cold or the furnace short cycles, or if the house gets noisy and pressure-y when the blower kicks on. If those match what he told you, he was reading your actual house, not running a script.

On the trash-talker, yeah, walk away. The email-quote guy too. A quote without eyes on the ductwork and gas setup is a number pulled from a menu. A fourth opinion from a smaller independent shop is usually worth it. The big names run heavy commission-based sales and thier quotes reflect that. Check if your area has any one or two person operations, they often quote lower because there's no sales layer at all.

Service plans are mostly margin, but not entirely useless. What they actually buy you is priority scheduling during the first cold snap when every company is slammed. If you're putting in a new furnace under warranty, an annual check keeps the warranty conditions happy with most manufacturers. I'd skip it at signing, run the first winter, and decide after. They will happily sell you the plan next fall for the same price, that offer never expires.

Been through this dance a few times over the years, and the thing I learned the hard way: ask for references from installs done in the last year or two, then actually call a couple of them. Any outfit that's been around will have a list ready. The slick sales types hate that request becasue their happy customers are mostly from five years back before the sales staff turned over. Also, don't buy the furnace itself from a salesman. When I replaced mine a while back, I had the ductwork checked by a seprate guy who does nothing but ducts, then let the installer quote just the equipment swap. Cheaper and I knew which half of the job I was actually paying for.

When I was in the same spot a couple winters back, the thing that actually settled it for me was a cheap anemometer off the internet, like thirty bucks. I walked around holding it up to each register before the contractors even showed up, wrote down the readings, and compared them to what each guy told me. The company that turned out great already knew the back rooms were starving for air and had a plan for it. The cheap quote guy acted like everything was fine until I showed him my own numbers. Funny how fast the sales talk stops when you've got measurements on paper.

One thing I'd add on the timing side: if you can limp through this winter, get the quotes again in like May or June. We held off on ours a couple years back and the off-season number came in way lower than anything we'd heard in the fall. Companies are hungry when nobody's calling. Also watch for the 'that price is only good till Friday' bit. Any legit installer will honor a quote for weeks, not days. If they're rushing you, that's your answer right there.

Update: went with the guy who did the full measuring and explaining. I took the references advice and called two of his past customers, both happy, so that sealed it. Install is done and the house actually heats evenly now. I'll still get fresh quotes in the spring for the AC side and see if that off-season pricing thing holds up.