easy answer...100 KBTU at 95+% eff furnace...5 K or 4 K rated blower depending on size of AC...what is cooling load?...I would suggest a 2 stage AC condenser...yes, I know more bux...you do want a matching 2 stage thermostat for furnace!...add a return(s) to lower level.

IMO

If heating is more of a concern to you why are you upsizing the 4 ton AC to a 5 ton AC?

Given that the 4 ton AC has been there so long what is the reasoning behind increasing the size?

Heating wise you could go back with an 80% 2 stage variable and be fine given that you claim you have 4 mild seasons. If your current furnace is a condensing furnace then the jump to 90% or higher efficiency furnace is more of a matter of preference.

Given that your seasons are mild, I doubt a higher efficient furnace above that of an 80% 2 stage variable speed will ever pay for itself. Unless there is some legal matter that is forcing you to go to a more energy efficient gas furnace such as the EPA regional efficiency standards mandate... there is little reason to do it in my opinion. If you were in Chicago, Minnesota, Montana etc. then the discussion is completely different.

The sizing of the furnace would be dependent upon the load of the structure and if short cycling has been occurring the 2 stage part of the new furnace will rectify that as it will run in low fire under those scenarios.

Why the increase to a 5 ton condenser? What were the results of the cooling load calculation?

The fact that you have to run a dehumidifier to keep the humidity below 50% suggests that the current 4 ton AC is short cycling and not doing a good job of lowering the humidity. If you were install a 5 ton condenser, which I think would be a mistake, then you will need to increase the duct work to supply the 2000 CFM of air flow. To do this properly you should have two 25 X 20 filters at a minimum.

The lower level needs a return in my opinion. Investigate if that is feasible and get a quote on the cost.

All 3 quotes state that I should have a 5-ton air conditioner. 1 guy said I needed a 4.5 ton air conditioner but they don't make that so a 5 ton it is. It doesn't get that hot here in the mountains so a single stage air conditioner is fine with me. My Tempstar 4 ton air conditioner has worked well all these years.

All 3 quotes, actually 2 quotes from Trane dealers, 1 quote from an independent guy who quoted both Carrier and Comfort Maker, all quoted 100 BTU 2-stage furnace 96% efficient. They are mid-grade units, i.e., not the high end fanciest communicating furnace and air conditioner but still $11k or more.

The lower level is finished so it will be difficult to add any duct work. The dehumidiflier only runs when the humidity is above 50% (eg: when it rains). I go to the lower level once a week to do my exercise and watch movie.

I don't know the cooling load calculation. 1 of the guys who quoted me the Trane system said they can potentially add a return in the lower level. Another Trane quote includes the "return" but that quote is almost $13k for a 5-ton single stage air conditioner and a 100 BTU 2-stage furnace with ECM.

I guess the fact that your 23.5 year old 4 ton Tempstar AC kept you cool in the past means nothing to these contractors. These professionals are telling you you need a 5 ton condenser and no increase in duct sizes. I suggest you look for other HVAC contractors. These guys are looking out for their interests and not yours.

I never want to see a 5-Ton A/C in a home, you can't size the filter rack area large enough & the duct-work is always way too small; especially not enough Return-air duct size &/or grille size. Judging by the need for dehumidifier I'd say a 3.5-Ton would be plenty large enough. I am betting a 60,000-Btu/hr furnace would heat your home just fine!

Have others help you and do your own FREE heat & Air load-calc.

www.loadcalc.net/

Thanks everyone for your input. I think the 3 contractors/dealers are tired of me asking questions. I've decided to go with the Trane system, 5-ton single stage air conditioner 15 SEER, 120k BTU 2-stage variable speed 96% efficient furnace. The HVAC contractors are pretty much the same in this area, the one I signed up with is a big outfit and has good reviews.

My house was custom built 23.5 years ago, the Tempstar system was sized for the 2,900 sq' main level (I knew nothing about building a house, there wasn't any HGTV back then). The system has served me well, the current furnace uses a 24" x 24" filter, I think they told me the new one will use a 20" x 25" x 1" filter (will believe it when I see it). The current duct work should do fine, I hope. I had an emergency repair in January when we had an unusual cold spell of 10 degree days for 10 days straight and the exhaust blower died. Cost $891 for the emergency repair (luckily they were able to locate a replacement exhaust blower the next day). The Tempstar dealer was worthless, they told me my furnace is too old, that they don't make those parts anymore and other parts will start to fail too. It was the Trane dealer who did the emergency repair at night and returned the next day with the replacement part (they repair all brands of HVAC). They will be the one to replace my HVAC system. Figured that it's time to have a new HVAC system for peace of mind.

100k BTU furnace supposedly will keep the house at 72 F when temperature is 16 F outside, that the numbers they use for Asheville, NC for sizing the furnace. However, there are days in winter that temperature can dip below 10 F or less, and with climate change you just never know. The 120k BTU 2-stage variable speed with ECM furnace will keep the house above 72 F even if it is 0 F outside (that's what my Tempstar furnace has been doing all these years). Anyway, I put 50% down already, just waiting for the install.

This Trane dealer will also cut 2 holes in the main return duct in the lower level to put in 2 returns. The main return and supply lines are both at the ceiling of the lower level, bisecting the length of the finished basement - both lines easily accessible. They will charge me time and material for the 2 "returns", shouldn't take that long to cut 2 holes in the main return duct to insert the return registers.

too bad, a mistake in the furnace size selection...you are being misguided by your dealer...more is not better...

IMO

If you go with any furnace 90% or above, these are condensing furnaces. They are also 'communicating' more often than not, but they can also be wired for legacy controls.

With that said, if you don't buy the communicating AC unit it's not going to really perform as well as a full communicating system in that both the furnace and AC are communicating capable pieces. Even a communicating furnace and the AC can be wired to run with legacy controls... but it's not in your best interest to do things this way.

A communicating system for your area is probably over kill, unless you travel a lot and need a way to control it from any where in the world, from a internet capable device such as cell phone or computer.

yes Mike, and sizing of equipment is not the only concern... but also the duct system it is attached to.

have to agree...if 5 ton condenser without ductwork changes, probably noise and other issues...

IMO