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  1. #1
    Join Date
    Jan 2008
    Posts
    7

    Supply Air Bypass ???

    I am having a new house built and am putting in a Trane 2 stage forced air furnace and 3 zones controlled with dampers in the ductwork. I inspected the HVAC work yesterday and found that the contractor installed a connecting duct between the supply air and return air plenum. He said this was required to prevent the motor from overheating. The bypass doesn't have a damper and is 8" in diameter. This seems rather big and is it even required??? I feel that on high speed there will be alot of air bypassed that won't make it out to the rest of the home where it's needed. Does anyone know the purpose behind this and can I get rid of it??

    Regards

  2. #2
    Join Date
    Feb 2008
    Location
    Dallas & Longview, TX
    Posts
    629
    I'll let the pro's address the lack of damper but the purpose of the connecting duct is the relieve the excess cfm when only one zone is called for. The recirculation of conditioned air straight back into the evap. coil is also a potential problem that needs addressing.

  3. #3
    Join Date
    Jan 2008
    Posts
    7
    In my case I live in a climate that doesn't really require AC so I'm not installing it. So at least the evap coil won't be an issue.

    Thanks for the reply.

  4. #4
    Join Date
    Aug 2003
    Location
    Lincoln, Nebraska
    Posts
    1,051
    On a zone system you need to have a bypass so that when the smallest zone is calling only the extra air has someplace to go. This should have a barametric damper installed in it. The size is dependent on your zone sizes. Besides not having a damper it sounds like they did the right thing. Sizing ducts and the bypass is critical for the system to operate properly.
    Its a good Life!

  5. #5
    Join Date
    May 2007
    Location
    Naples, Fl
    Posts
    889
    What brand zoning. Get with the contractor an query the design I won't say it's wrong but see what the zone manufacturer says.

  6. #6
    Join Date
    May 2008
    Location
    newnan,ga
    Posts
    57
    kilgore said it perfectly. I would ask your contractor why he didnt put dampers in the bypass.

  7. #7
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,922
    Should have at least a barometric damper for when all the zones are calling.
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  8. #8
    Join Date
    Dec 2002
    Location
    Houston,Tx.
    Posts
    15,962
    IMO, I think two systems would be better than zoning any day, cool the bedrooms at night and the play rooms during the day no loss whatsoever, or bypassed conditioned air re-entering the system that is getting in the way of un-conditioned air trying to enter the system. Regardless of what anyone thinks air does take up space, and the bypassed air will somewhat restrict the new un-conditioned air entering the system, this does not take Rocket Science to figure out, zoning is a trend that has it's good and bad but trust me it's long from being perfected if your still using a bypass.
    __________________________________________________ _______________________
    “Experience is a hard teacher because she gives the test first, the lesson afterwards". - Vernon Law

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  9. #9
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Bypass should have a barometric damper at the minimum.

    Bypassed air does not get it the way of unconditioned air trying to enter the system.

    If the fan supplies 1200 cfms and 400 hundred is bypassed back to the return duct,the return will only draw 800 cfm from the conditioned space,as 400 cfms is coming from the bypass.So there's no air to get in the way of.Supply and return cfms thru the equipment are always equal,a bypass doesn't change that ,or create "new" air.

    May not be rocket science ,but there's some science involved.

    russgs,

    Use the search function on this site to read more about zoning,plus google to find some manufacturers sites that explain more about a bypass and zoning in general.Zoning has been around a long time,and works very well,if and only if,it's designed and installed correctly.Those that know how ,have no issues with zoning systems.

    Carrier even has one the that doesn't require a bypass,nor can one be used with it.Other brands will likely have the same soon.

  10. #10
    Join Date
    May 2007
    Location
    Naples, Fl
    Posts
    889
    Quote Originally Posted by Mr Bill View Post
    IMO, I think two systems would be better than zoning any day, cool the bedrooms at night and the play rooms during the day no loss whatsoever, or bypassed conditioned air re-entering the system that is getting in the way of un-conditioned air trying to enter the system. Regardless of what anyone thinks air does take up space, and the bypassed air will somewhat restrict the new un-conditioned air entering the system, this does not take Rocket Science to figure out, zoning is a trend that has it's good and bad but trust me it's long from being perfected if your still using a bypass.
    Is this an endorsement of the Carrier Infinity zoning? Now that is cool. And I thought it was Rocket Surgery.

  11. #11
    Join Date
    Dec 2002
    Location
    Houston,Tx.
    Posts
    15,962
    Anyone that thinks bypass air does not interfere with the normal return is feeding you a line of BS from El Paso to Miami, A two year old knows that if you filing a box with normal return air at so many cfm's or even fpm if you are "pumping" in air from another source to that same return it does interfere some and does cut down your "normal" air your system would be returning, God why do the Blue Oval brainwashed folks live in such denial?
    __________________________________________________ _______________________
    “Experience is a hard teacher because she gives the test first, the lesson afterwards". - Vernon Law

    "Never let success go to your head, and never let failure go to your heart". - Unknown

  12. #12
    Join Date
    Dec 2002
    Location
    Houston,Tx.
    Posts
    15,962
    Quote Originally Posted by adrianf View Post
    Is this an endorsement of the Carrier Infinity zoning? Now that is cool. And I thought it was Rocket Surgery.
    The day I endorse the Infinity I will have to forget all my morals and pack tubes of KY on my truck to hand out to my customers, I will never be that hungry, that system is "WAY" over rated and your service company should give you an extra board you will eventually need it Google that will you.
    __________________________________________________ _______________________
    “Experience is a hard teacher because she gives the test first, the lesson afterwards". - Vernon Law

    "Never let success go to your head, and never let failure go to your heart". - Unknown

  13. #13
    Join Date
    May 2007
    Location
    Naples, Fl
    Posts
    889
    Quote Originally Posted by Mr Bill View Post
    The day I endorse the Infinity I will have to forget all my morals and pack tubes of KY on my truck to hand out to my customers, I will never be that hungry, that system is "WAY" over rated and your service company should give you an extra board you will eventually need it Google that will you.
    That was alot tamer then I expected. A tech is on such a call right now.

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