Oh my, this oughta be good.
I just went through the furnace/ac replacement fiasco.
I replaced a 17 year old 100k btu 70% Payne (carrier contractor grade) with a 90k btu 80% two stage Carrier Infinity. It was substantially colder in January when the Payne was still in operation, yet my February and March gas bills with the new furnace were actually higher.
I'd check the rebates available from the manufacturer and from the utility companies, then check how much it'll knock off your gas bill over the next ten years. For me it was about an $80-100 a year benefit to go from the 80% to a 92-94% which would have cost me about $1200 more. I put that money towards a two stage variable fan system, which gives a lot more comfort.
Then make sure you dont have a dimensional problem. 90%+ furnaces have a secondary heat exchanger that can add a foot and a half of required space. They also cannot use your old vent for CO...they use a 3-4" pvc pipe that has to be vented through the roof or an exterior wall. If through a wall, make sure you know what the code requirements are for clearance. Around here the pipe has to protrude from the wall a distance further than any roof overhang and be a certain distance off the ground.
Then make sure you understand the increased complexity. The 90% units have two heat exchangers vs 1, a forced air venting system, and a lot of extra parts.
Installation wise, there seem to be some really top notch installers, a lot of guys who can get it hooked up and working but the quality of work leaves a lot to be desired, and a handful of guys that have no idea what they're doing.
Problem is, you cant tell the difference between them unless you know as much as the experts. Good luck getting help with the expert web sites...they dont think much of homeowners, and many of the sites prohibit discussing prices or how things exactly work with non tradespeople.
I went through a long vetting process of gathering word of mouth and recommendations from local discussion forums, weeding out companies with lots of BBB complaints, and then had 5 come out to the house. A few basically werent going to tell me what equipment they were recommending or how much it'd be due to some sort of fear that I'd use their quote to leverage someone else. Some wanted to send salesmen out to give me a 3 hour dog and pony show but without disclosing a quote unless I was willing to give them my business...before I knew what they'd be putting in.
Once I'd finally winnowed down the ones that actually would produce a quote...they were all around the same price.
The hard part was equalizing their quotes. Warranties all over the place, some stuff included and some not, some stuff that they would charge extra for if it took too long, etc.
Aside from your 90%+/80% question, heres what I learned and what I'd do again:
- Do not mix equipment from different companies...use the same brand for furnace, air conditioner, air cleaner, coil, thermostat etc. Just. Dont. Do. It.
- Most of the equipment is about the same in terms of quality. Carrier and Tranes top of the line setups have some comfort benefits but you'll pay for them.
- I'd get a unit with a variable speed fan before I'd spend the money on a 90%+ furnace and make sure I get a thermostat that will let me control it. We run ours 24x7 on low, it takes 80 watts of power, and we have no hot or cold spots in the house. The VS motors are very reliable and last a very long time, and use much less electricity.
- Make sure you get a FACTORY/MANUFACTURERS warranty for at least ten years for parts AND labor thats transferable to another dealer. I saw no end of shenanigans with warranties with offering parts only, or the labor was in there but only if you had it done by the installer, etc. No two were alike. Most will throw in the ten year manufacturers P&L warranty to get the business.
- Make sure your dealer is factory and NATE certified
Then put the cheapest thing in that you can get a quote on, and if the installer screws it up...the manufacturer will have to solve that since they certified them, and if it breaks for the next ten years, you're covered. If the installer cant perform to the warranty, move it to another company until you find one you like.
I picked a company with a great reputation thats been around a long time, bought high quality expensive equipment, and basically nobody at the place could find their ass even if they used both hands. After 2 months of screwing around with the equipment I made them remove everything and re-do it. Today I found out that they didnt submit the paperwork for my utility rebates and so far they're not returning my calls.
Were I to do it all over, I'd get a Goodman furnace with a VS fan, two stage since IIRC you live in a cold area with a long heating season. Find a factory authorized dealer thats NATE certified that gave me a low bid to install it, and get the 10 year P&L warranty. Goodman is a lot less expensive than the bigger brand names, has had some historical reliability issues but those are from many years back, and currently makes a very good furnace and excellent air conditioners. Their VS furnace uses the same motor and controller as my expensive carrier unit. They offer one of the best warranties in the business. Big problem is getting someone to quote you one...everyone carries Goodman and another big name brand like Lennox, Carrier or Trane and they'll all try to upsell you to the big name brand.
If you do fall in love with a Trane or Carrier, buy their sub-brand and save a thousand bucks. Trane is made by American Standard and the AS units are almost identical, yet cheaper. Carrier also makes Bryant and again the Bryant is identical but a lot cheaper.
If you're not excited about the Goodman option, look at a Bryant Evolution system. Most of the pro's like the Carrier Infinity/Bryant Evolution and the Rheem/Ruud Mod furnaces. The latter set are complicated to install, so make sure you get a dealer that knows them well and isnt going to use you for a guinea pig.
