Results 1 to 6 of 6
  1. #1
    Join Date
    Oct 2008
    Location
    Michigan
    Posts
    29

    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

  2. #2
    Join Date
    Jun 2007
    Location
    south carolina
    Posts
    176
    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.

  3. #3
    Join Date
    Oct 2008
    Location
    Michigan
    Posts
    29
    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...

  4. #4
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    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!!!!

  5. #5
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,903
    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.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  6. #6
    Join Date
    Oct 2008
    Location
    Michigan
    Posts
    29
    Should a "static" test be done uising the current system or only after installing a new system since the blowers may be quite different...

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event