feedback on new furnace and ac design

[dwichman]

Hello all,

I've had several reputable contractors come in and each give me different advice on upgrading my 40-year-old GE furnace, adding ac and reworking some ducts to accommodate a zoned system for up/down stairs. Out of the 6 contractors I was hoping a few would say the same thing and make this easy on me, so now I turn to the Internet to hopefully get some 2nd opinions. Most of my uncertainty is in the duct work to handle the zoning and get enough air upstairs which is currently not even adequate for heat IMO.

Current configuration:

1900 sq ft 3 bed 2 bath 2 story home, furnace is in the garage with:

upstairs:
* 10" round into 5x14" supply trunk following stairs up to second floor feeding 5-6" ducts to floor/wall registers into master bed, master bath, second bath and 2 smaller bedrooms.

* 8" round into 3x12" supply feeding single floor/wall register in upstairs hallway

* 10x14" return trunk into upstairs attic feeding 1-8" ceiling register in MBR, 2-6" ceiling registers in 2 smaller bedrooms, and 1-10" register in hallway ceiling

downstairs:
* 14" round supply going into crawlspace to feed 3-8" floor in kitchen, dining and living, and 2-6" floor registers in family


The most logical plan I've heard is:

upstairs:
* keep 10" round to 5x14" trunk feeding 5 floor registers as supply and put a zone damper on it for upstairs zone

* change 8" round to 3x12" supply feeding register in upstairs hallway to return and upsize to 6x12" to accommodate the next bullet

* change 10x14" return trunk feeding ceiling registers into supply trunk with damper for upstairs zone. cap 10" ceiling register in upstairs hallway. add another 8" supply into MBR (total of 2). upsize 6" supplies to other two bedrooms to 8".

downstairs:
* stays the same and gets a damper for downstairs zone


Furnace would be trane xl80, or xv95 with honeywell 322 to control zones and stages, 6" bypass (seems small). Trane 4 ton 13 seer ac.

Other contractors have suggested:

* not re-using floor ducts to upstairs?

* don't change/reconfigure ducting at all, floor ducts are adequate

* add another supply duct into attic for more supply registers

Phew! I know that's a lot to take in. Just looking for some other opinions as I'm sick of talking to contractors.

Thanks for taking the time.

-D

[udarrell]

You are asking us to do a big job free, - that could even be a DIY.(?)

Though I usually help nearly everyone, - this seems a bit much for us to be doing from here, as we're not supposed to enable DIY'ers.

Someone ought to get paid to do a job of that size.
I don't want to go to the drawing table tonight.

Forgive me; perhaps I went a bit overboard!

Good Luck... :pop:

[BaldLoonie]

4 tons for 1900 sq ft seems pretty steep unless you are in a very hot climate.

So a 14" round feeds the downstairs? That's about 2 tons worth of airflow. How does he propose to stuff 4 tons worth of air into it? That poor A/C is going to short cycle like a turn signal when 1 zone is calling. Same with upstairs. And to move 4 tons of air, you'd need a 100K XV95 which sounds way oversized for 1900 sq ft in a warm climate...

Zoning an existing system usually is a mess. About the only hope might be Carrier's Infinity system with equipment sized right on or a hair small.

[Paul12644]

Wow, how did you get 40 years out of a GE furnace? Everything I touch that says GE has a short life. But then again, maybe 40 years ago they built good stuff.

[beenthere]

I don't see where you said they are installing return to make up for the return you lose when you make it into a supply.

I think you need to keep calling contractors. Cause it sounds like a system that will never work right from your description.

[dwichman]

DYI? For sure not. I'm already involved way more than I care to be. If I would have heard a consistent story among the contractors I would have just gone with it.

An existing 3x12" supply will be switched over to a 6x12" return that sits near the floor in the upstairs hallway to make up for removing the 10x14 return that goes into the attic.

It's not terribly hot here (San Jose), but it does get into the 90's for a while during the summer. Most contractors were recommending 3.5 to 4 ton. One recommended a 3 ton. But he also told me that the 5x14 that feeds the upstairs floor registers is enough for a single zone with no bypass!

Even if there's a sufficient bypass will the ac and furnace continually be switched off by the temperature sensor when only one zone is calling? Is this a bad thing?

Thanks for the info.

[beenthere]

Changing one supply to a return. isn't gonna make up for all the returns they are switching to supplies.

Short cycling of the A/C and furnace will cost you money in electric. And can shorten the life of the A/C. And some furnace parts.

[simplyrollin]

I would hate to attempt to install a zone on this one!

[usskaufman3]

The simpliest solution for me, would to have two complete systems. One for upstairs and one for downstairs. You wouldn't need 4 ton ac to do this and this would solve your zoneing issues.