Question: Duct sizes are smaller than recommended
So the last quote added on duct work that previous quotes didn't. The questions are:
1) What would happen without upgrading the ducts.
2) Do installers reduce air flow to improve static pressures or would this damage the HX?
3) How does this affect cooling?
The idea of replacing the furnace on a 20 year old home is starting to get really expensive if I use the last quote...
Design considerations: 100K 95% VS 4TON/1600CFM (e.g., York) Michigan
A York installation manual (since I can't find a Bryant) seems to indicate that my return and supply ducts are quite undersized.
Return is 32x8 feeding into a 25x8 plenum. The manual wants 360 in^2
Supply is 24 X 8 + 2-6" rounds. This gets close to the required 280 in^2
if the duct work is too small for a york then it's too small for a bryant. Your in michigan so i'm guessing you have metal duct. In my oppinion I don't change metal duct unless it has become a problem. If your certain your duct is under sized then you should probably get it taken care of. If it doesn't have a size issue and it isn't falling apart then your fine.
Thank you for the comment. My current 120K 70% furnace has worked well at heating and cooling the house for the past 10 years that I've owned it. No issues caused by the ducts and they're not falling apart or anything like that. My concern is that if I upgrade to a new furnace and the ducts are smaller than what the installation manual calls for, will this cause premature failure of the furnace or some other mis-operation. The question is raised because only one of four contractors cited the return duct as needing to be upgraded and when I checked a furnace manual it seemed to support his statement. Makes me wonder if the other contractors are doing their job or if this really isn't an issue...
What manul,what did you read??
Have a contractor check the static ,resistance to air flow of the cooling coil and duct system.If it's to high then you need some duct remediation.
Keep calling until you find someone that can check the static!!!!
Most houses have oversized furnaces.
Strange that yours comes out that the old furnace was sized right.
It happens once in awhile though.
Yep, that 100,000 needs larger duct then your old furnace did. Or else it will be loud in second stage.
Should a "static" test be done uising the current system or only after installing a new system since the blowers may be quite different...