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  1. #1
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    Question What about bypass humidifiers?

    Not to kick over the old anthill, but...

    Same system, didn't have a bypass installed thanks to the good advice found here.

    But now we want to install a humidifier, and we got a recommendation for the Aprilaire 600, which is a bypass humidifier that uses a 6" round duct to create a bypass. It has a manual (non-barometric) damper, which you open in the winter and close in the summer.

    Since a bypass (especially one that's always open) will reduce the net airflow, is this a terrible idea, or is the bypass small enough that it shouldn't be a problem?


    (Incidentally, the tech who came out said we really should install a bypass anyway to keep our zoning system from overheating. Sigh. If only I could find someone in my area who knew what you folks know.)

  2. #2
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    Made this its own thread. You are not permitted to post in other peoples threads in the AOP forums. Please read our site rules, thank you.
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  3. #3
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    Quote Originally Posted by beenthere View Post
    Made this its own thread. You are not permitted to post in other peoples threads in the AOP forums. Please read our site rules, thank you.
    This was my thread. I just lost my password and don't remember the mail I used to sign up originally.

    And my current question is based on the advice I got last time, so I'm looking for an answer given that background.

    But since you preemptively made this its own thread, I'll clarify the question for newcomers:

    As mentioned in the initial post, our furnace is zoned and as a result short-cycles. We replaced a cracked heat exchange, and the repairman's opinion was that it was due to overheating & short-cycling. He recommended a bypass to alleviate the overheating. After a vigorous HVAC-Talk talk debate here, I decided not to get a bypass, since it reduces the net airflow and thereby makes the overheating problem worse.

    In light of that, is a bypass-based humidifier a terrible idea, or is it a small enough bypass that the reduced airflow won't make things appreciably worse? Or will the humidification actually help?

  4. #4
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    IF you're already marginal on airflow due ot a zoned system/oversized furnace... or single stage only, then spend hte extra and get a fan powered humidifier for just a little more. I think they can normally be powered off the furnace cotnrol board.

  5. #5
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    Quote Originally Posted by motoguy128 View Post
    IF you're already marginal on airflow due to a zoned system/oversized furnace... or single stage only, then spend the extra and get a fan powered humidifier for just a little more.
    Where do the fan-powered humidifiers get their air supply? With a bypass, I know I'm getting living space air.

    It looks like the fan-powered humidifier might pull in basement air? Would that even work if my problem is high static pressure? (Or would the main fan end up blowing air out the humidifier?)

  6. #6
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    Quote Originally Posted by pjc4 View Post
    This was my thread. I just lost my password and don't remember the mail I used to sign up originally.

    And my current question is based on the advice I got last time, so I'm looking for an answer given that background.

    But since you preemptively made this its own thread, I'll clarify the question for newcomers:

    As mentioned in the initial post, our furnace is zoned and as a result short-cycles. We replaced a cracked heat exchange, and the repairman's opinion was that it was due to overheating & short-cycling. He recommended a bypass to alleviate the overheating. After a vigorous HVAC-Talk talk debate here, I decided not to get a bypass, since it reduces the net airflow and thereby makes the overheating problem worse.

    In light of that, is a bypass-based humidifier a terrible idea, or is it a small enough bypass that the reduced airflow won't make things appreciably worse? Or will the humidification actually help?
    Adding a bypass humidifier to your system as is will exasperate your current problem by adding hot undiluted air back through the heat exchanger.

    Find a company to correct the zoning or disable it.

  7. #7
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    Quote Originally Posted by pjc4 View Post
    Where do the fan-powered humidifiers get their air supply? With a bypass, I know I'm getting living space air.

    It looks like the fan-powered humidifier might pull in basement air? Would that even work if my problem is high static pressure? (Or would the main fan end up blowing air out the humidifier?)
    No, the fan powered unit are just like the bypass, but draw their air form the airstream and use a fan to circulate it across the humidifier pad then back into the air stream.

    http://yourhome.honeywell.com/home/P...Humidifier.htm

    http://www.aprilaire.com/index.php?z...ory=5&item=700

  8. #8
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    Bypass units are much simplier than fan powered and therefore cheaper to keep up. We only sell bypass units and have had good luck. If you've got a zoned system, you may need to leave damper nearly closed to keep from having moisture "blown" thru the humidifier.

  9. #9
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    Quote Originally Posted by pjc4 View Post
    This was my thread. I just lost my password and don't remember the mail I used to sign up originally.

    And my current question is based on the advice I got last time, so I'm looking for an answer given that background.

    But since you preemptively made this its own thread, I'll clarify the question for newcomers:

    A
    Ah. Please contact the Admin. And decide if you want to continue using this current user name, or the other one. Your not allowed to have 2 user names. Its in the rules

    From the site rules:
    10. One Registration Only

    As the board gets larger, it becomes more important that each member has only one registration name. Any member who signs up under a new name will be banned from the site. If you feel you have to re-register with a new name due to a technical problem, be sure to get it okayed by the Site Administrator first. To find the Site Admin follow this link hvac.talk@gmail.com

    I'll hold off on the banning. So that you can contact the Admin.
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  10. #10
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    Quote Originally Posted by motoguy128 View Post
    No, the fan powered unit are just like the bypass, but draw their air form the airstream and use a fan to circulate it across the humidifier pad then back into the air stream.
    Thanks -- it took me a while of looking at the diagrams for the Aprilaire 700 to figure out that it pulls air from the supply on either side of the water panel, and then blows the air through the panel back into the duct.

    Unfortunately, now the problem is that the only place I can fit the humidifier is at the top of the supply plenum, from which 2 of the 3 zones branch horizontally. (The 3rd zone branches out below this point, right next to the AC coils.) Aprilaire says the 700 needs to be installed in vertical airflow. Is this (the end of vertical airflow) close enough? Is the placement of the 3rd zone a problem?

  11. #11
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    Quote Originally Posted by second opinion View Post
    Find a company to correct the zoning or disable it.
    Everybody who has come out has recommended a bypass, which is completely wrong, as you and others have pointed out.

    I don't have the vacation time (or the money) to keep calling out endless technicians who don't know what they're talking about. How can I find someone who actually knows what they're doing? What questions do I ask on the phone? How do I talk to right person? How do I make sure they send someone qualified to assess and address the problem?

    (The guy who installed it apparently knew enough not to install a bypass, but he was a total flake about showing up, repeatedly forgetting appointments.)

  12. #12
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    Needing a humidifier is often a sign that your home has too much air infiltration. The best first step is to find out how much & where your home is leaking air and then air seal. A properly air sealed home may very well create enough moisture internally so that a humidifier is not needed.
    An answer without a question is meaningless.
    Information without understanding is useless.
    You can lead a horse to water............
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  13. #13
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    Quote Originally Posted by pjc3 View Post
    Everybody who has come out has recommended a bypass, which is completely wrong, as you and others have pointed out.

    I don't have the vacation time (or the money) to keep calling out endless technicians who don't know what they're talking about. How can I find someone who actually knows what they're doing? What questions do I ask on the phone? How do I talk to right person? How do I make sure they send someone qualified to assess and address the problem?

    (The guy who installed it apparently knew enough not to install a bypass, but he was a total flake about showing up, repeatedly forgetting appointments.)
    Post your geographical location and check the dealer locator in the index on this site.

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