Your HVAC contractor should be giving you advice that's responsive to your needs and wishes, not just quotes on the equipment they want to sell you. If you're not getting that, you maybe should find another contractor to work with. You say you've done insulation work. Does that mean that your house is now tight and well insulated, or is it just no longer a drafty 100 year old house lacking insulation?" If you've done little or no duct sealing and air infiltration sealing, I'd spend money on those things and buy a cheaper (maybe even single stage) furnace, Even a two stage furnace is going to have longer blower runs, and if you have duct and air infiltraction issues, that isn't a good idea. $500 of duct sealing and caulking, etc., can do wonders. The older your duct work is, the more likely you've got lots of leaks and gaps.

I did a quick search on the AS site for opf10w and found no information. I would suspect a 2.5 ton a/c would be excessive, unless you have zero insulation and questionable construction. Recommend that you have a heat calc done (or do yourself [hvac-calc.com]) to determine your heating/cooling needs. I (sorry for all of the I's) also searched for the Chronotherm 111 stat, but there are many models (do you have a model number--may be on the back plate)? The information that I found was not sufficient to give you an informed answer. If your stat is a single stage unit, most 2 stage furnaces will work on a timer on the control board (not the best way). A 2 stage stat gives you better comfort and efficiency. I would get some more estimates. V

I was able to get info on the existing furnace from the data plate. It's a Carrier Model 58ss140-BC, Series 110, 167,000 BTU. The data plate said the blower is "157", whatever that means. The motor spec was 1/2 hp. Mfg date 1982. That's all I found on the furnace. I found next to nothing on the a/c. The data plates outside are gone. I could see where it was but there was just rivets. A single, long rectangular unit outside. Like I said, vintage 1974, from the builder. According to my mother, the quoting contractors guessed that the system was 4 or 5 tons. I don't know anything about who said what. Turns out the Lennox/Costco guy was the only one to quote an upgraded unit. He also quoted: Option #3B. $9,185. Platinum Package. A/C XC17-048 and 2 stage gas furnace SL280UH135 with variable speed and I-Comfort Communicating Controller. I'm having a hard time getting her to look at the Am Std quote because they didn't quote her an upgraded unit option and their basic units were only about $1,000 cheaper than the upgraded Lennox units. ($9,145 vs $7,945). About the house, I tried to describe it above. Built 1974. 3200 sq ft. and two stories. Attached garage. Full sun exposure--the property is not shaded. Brick exterior with not a whole heck of a lot of insulation. (I remember my parents being mad that the builder gipped them on the insulation.) High quality house though, expensive neighborhood. Stick framed over a full basement. Attic with pitched shingle roof. Colonial. Original single pane wood windows with storms windows, maybe a tad drafty. After being widowed with 4 kids in 1978, she never had the money to remodel anything and everything is pretty much 1974. Anything else you want to know about the house, please ask. This is all I could think of.

I may get dinged for saying this, but they are both reputable manufacturers and the efficiency ratings are comparable. I believe you would benefit yourself by selecting by the service provider you trust more than the manufacturer's equipment. The primary difference between any two installations is the service provider. If virtually anyone's equipment is properly installed it will operate well for around 15 years (ASHRAE estimate). If it is installed by a contractor that is either unqualified or just doesn't care, you will have problems from now on. Ask around and find someone you can trust to install it properly and back their work. You will be glad you did. I have written an article on this very subject. I think it's pretty good information for anyone about to replace heating and air equipment. Here it is. Air and Energy Solutions. Again, Trane and Carrier are both reputable and either piece of equipment, if installed properly will serve you well.