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Thread: Humidifier Bypass

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  1. #1
    DIY Junior Member mcnauge's Avatar
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    Default Humidifier Bypass

    Hello,

    Im in the process of installing a new humidifier, however, due to the way the furnace was installed the Furnace output duct has the A-coil mounted about 14" above the furnace top and this leaves very little room above the A-coil and the ceiling.

    1) Can I mount the bypass duct below the A-coil (All the manuals say 6" above the coil, but i assume that because usually the coil it right above the furnace.

    2) Can the bypass duct be 5-6" highier or lower than the humdifier? (I have a space issue on the supply and return lines and can't mount them level to eachother).

    Thanks,
    Erik

  2. #2
    DIY Senior Member SteveW's Avatar
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    Default

    Quote Originally Posted by mcnauge View Post
    Hello,

    Im in the process of installing a new humidifier, however, due to the way the furnace was installed the Furnace output duct has the A-coil mounted about 14" above the furnace top and this leaves very little room above the A-coil and the ceiling.

    1) Can I mount the bypass duct below the A-coil (All the manuals say 6" above the coil, but i assume that because usually the coil it right above the furnace.

    2) Can the bypass duct be 5-6" highier or lower than the humdifier? (I have a space issue on the supply and return lines and can't mount them level to eachother).

    Thanks,
    Erik

    1) Do you have a heat pump? If so, bypass has to come off above the A-coil.

    2) Yes. No need for the duct to be level.

  3. #3
    DIY Junior Member mcnauge's Avatar
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    It is a natural gas furance (about 5 years old). So does that matter is the bypass is above or below the A-coil?

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    DIY Senior Member SteveW's Avatar
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    So you don't have a heat pump?
    (I have a natural gas furnace and a heat pump.)

  5. #5
    DIY Junior Member mcnauge's Avatar
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    Its an all natural gas furance, the only add-on is the Air conditioning A-coil (its just for ac no heat pump)
    Last edited by mcnauge; 01-10-2010 at 06:25 AM.

  6. #6
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    it can come off below the coil.

  7. #7
    Retired Defense Industry Engineer jadnashua's Avatar
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    This is a furnace with a/c, not a heat pump situation, so especially if installed with a damper to shut off that bypass during the cooling season, it would not make all that much difference where it was tappped in. Yes, you will get more vapor per pass if the tap is into hotter air. If you locate the sensor well, you can control this.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  8. #8
    DIY Senior Member Runs with bison's Avatar
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    The issue being discussed at this stage was the placement on a heat pump system. That's what SteveW correctly pointed out and Hube disputed.

    I don't really need the sensor in mid winter. With temps running below 10 F daily average for a week the humidity dips down to the mid 20% range with the humidistat set to call for water the whole time. I can tell by touching both sides of the bypass piping that the evaporation is cooling the bypass gas stream greatly. It would barely work at all if it had zero preheating.

    I won't claim the house is tight, but it is considerably tighter than when I moved in.

  9. #9
    DIY Senior Member Hube's Avatar
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    At least the Moderator(Jadunashua) got it right...."we are not talking about a heat pump system at all.
    But even if it was a heat pump forced air system it can be installed any where on either the return air or the supply air plenums or main trunks.
    Also,the fact still remains that if the Humidifier is allowed to put air into the main air stream no matter where the by-pass is located, the home will still have humidified air injected into it via the supply ducts,etc
    Now do you get it?
    Last edited by Hube; 01-14-2010 at 05:52 PM.

  10. #10
    DIY Senior Member Runs with bison's Avatar
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    You still don't get it. The flowsheeting and heat/material balance issues have escaped you.

    One could do the same thing by putting a bypass takeoff loop in between the furnace exchanger and blower. And it wouldn't work as designed (contrary to your opinion.) Where the humidifier bypass is connected does matter. Just anywhere won't cut it.

  11. #11
    DIY Senior Member Hube's Avatar
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    been there, done that.
    Obviously you have not.

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