Natural Gas Furnace Help

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piejam

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Sep 18, 2011
230
Hello Gentlemen,

Hope I'm in the correct forum. Looking to replace 2- stage 1 split system ng furnaces..Spoke to a few vendors. Been advised of incorrect air duct sizing problems. House is 22yrs old. Pardon my french but my builder sucked. Two guys I won't even consider since they failed to perform heat load calculations. The third one will. Even took measurements of my windows facing south. Wants his engineer to visit and make suggestions. No charge for any estimates.

I am on a slab and zone 1 duct work is buried. This unit is 80k btu's. Zone 2 furnace is in the rear of the home on the first floor and supports the 2nd floor. My upstairs master bedroom and bath is Icey Hollow!. Zone 2 unit is 60k btu's. The house is 2900sq ft..1500 downstairs and 1400 upstairs..Builder shoe horned in the heating system for zone2 in a mechanical room that's more like a closet. the condensers are 3ton units.

Existing furnaces are single pipe systems. Contractor wants to move zone2 furnace to the attic. I have reservations since this is unconditioned space. Plus if I want a modulating furnace(more energy efficient?) how does one deal with the condensation issues? The vendor I like would built a platform for the unit to rest upon. Not suspended with straps from the rafters..How do you insulate the condensation line? Would not want to rely on heat tape, and besides is it smart to have a condensation pump up their as well?

The current loc for zone2 supply is not 16" more like 8x12 that sits on top of the a/c coil up into the ceiling. Guess that's why contractors want to move it and repipe into the attic. my questions are would an unconditioned attic put more stress on the unit? Should I stick with a 2stage non modulating system? Master bedroom and bath are vaulted so there is no attic to access the ductwork in these rooms..Should I consider a 3rd zone for these spaces and go ductless so I don't freeze my tail off? Dh passed away so I'm on my own. Any opinions would be most welcome..Thanks..
 
Hello PieJam,

I'm a HVAC contractor here in Middle Tenn. Sounds like a challenging setup you have there.

Sounds like the ductwork for upstairs is running between the floors and or in the attic.

I've tried installing Condensing furnaces in attics and will never do that again and it doesn't get that cold here.

You didn't say, but my 2 stage furnaces have ECMotors (Electronically Commutated Motor) that can make all the difference

in room temps being more even, plus, they overcome the small duct/high static problem.

Last resort is to put the 80% furnace/cooling coil in the attic and tie back into the ductwork or re-run all new ducts with ceiling vents.

Mr. Kool HVAC
 
MrKool

Thank you so much for chiming in. My inner sense tells me not to purchase a condensing furnace. Too bad since they seem to be the most energy efficient. Am looking for a variable speed motor as well. DH was impressed with Rheem. Currently have a Rheem setup. Existing units served well with limited problems. It's the duct work for zone2 is the issue(Upstairs)..

The supply to the upstairs goes into the attic and is distributed to the 4 bed 2 bath with some sort of flexible duct material. To me I feel its crap since I can't have them sanitized. Just may have to get the sheet metal guys to replace..Still in the planning stages..Like the idea of Rheem since units are tested at the factory not sure if motors are insulated. Believe me I will ask. Trying to view contractor chat rooms on HVAC issues.

Appreciate your sound advice. Mod furnace may not be for me since I am on a slab..Zone1 is in the center of the first floor under the staircase for upstairs. Noisy. I've gotten use to it but a bad feature for resale. Modulating furnace I believe will run more often at lower rate for longer periods. Don't get me wrong I know its about comfort and eliminating the cold periods between the furnace kicking in. Just a shame I can't take advantage of a better product due to poor HVAC design in my home!

Vendor#3 is coming back with his mechanical engineer so I'll see what they offer. At least this contractor just doesn't want to swap out equipment, he trying to figure how to make my house more comfortable despite a bad situation.

Never been to Tenn but is on my watch list since I just retired. My nephew and his family live in Memphis. Thanks again and have a great day!
 
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