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  1. #1
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    Can I use 2 flow-through humidifiers on the same return duct?

    I have a ~2400 sqft home with forced air heating (dual energy). Currently, I have a 12 gallon flow-thru humidifier on the return duct, but I am having trouble getting the humidity up in the house; it is consistently around 30-35%, and the house feels quite dry.

    Ideally, I would have liked to replace the 12 gallon with an 18 gallon unit, but unfortunately I don't have enough space on the return duct to fit an 18 gallon unit. I have a filter box at mid-point in the return and only provides me 16" of space above the filter and an equal amount of space below. My return duct is 16"x21". However, I would have space to fit 2x 12 gallon units; one on each side of the return duct.

    I've had an HVAC tech here for a quote, but was told that I couldn't use two units; they would somehow compete with each other. That my only choice would be to redo my return and move the filter lower down to make space for an 18 gallon unit.

    Is he right? Why would 2 units compete with each other and not provide additional humidity?

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  2. #2
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    When does the humidifier run?

    Connected to hot or cold water?

    Dual energy, meaning a heat pump with oil/gas?
    The Food Stamp Program, administered by the U.S. Department of Agriculture, is proud to be distributing the greatest amount of free meals and stamps EVER.
    Meanwhile, the National Park Service, administered by the U.S. Department of the Interior, asks us to "Please Do Not Feed the Animals". Their stated reason for this policy "... the animals become dependent on handouts and will not learn to take care of themselves."
    from an excerpt by Paul Jacob in Sun City, AZ

  3. #3
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    Quote Originally Posted by pacnw View Post
    When does the humidifier run?

    Connected to hot or cold water?

    Dual energy, meaning a heat pump with oil/gas?
    • Dual energy = heat pump + electric strips & oil furnace
    • Cold water supply
    • Humidiifer runs whenever the heat is on (oil or electric).

  4. #4
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    Have you considered a steam/electrode humidifier which can be mounted remotely?
    AOP Rules: Rules For Equipment Owners.

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  5. #5
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    Quote Originally Posted by benze View Post
    • Dual energy = heat pump + electric strips & oil furnace
      .
    That would be an oddity!!

    Are you sure there is strip heat?
    The Food Stamp Program, administered by the U.S. Department of Agriculture, is proud to be distributing the greatest amount of free meals and stamps EVER.
    Meanwhile, the National Park Service, administered by the U.S. Department of the Interior, asks us to "Please Do Not Feed the Animals". Their stated reason for this policy "... the animals become dependent on handouts and will not learn to take care of themselves."
    from an excerpt by Paul Jacob in Sun City, AZ

  6. #6
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    iF A 12 gal cant keep up Id look at ways of tightening that envelope.

  7. #7
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    Ive done it before.

    Only thing I would like to see is the bypass on both being as long as possible.

  8. #8
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    Quote Originally Posted by pecmsg View Post
    iF A 12 gal cant keep up Id look at ways of tightening that envelope.
    X2

    Though, the humidifier will have a greatly reduced capacity when the heat pump is running because of lower plenum temperature. That's where the steam humidifier is superior because it is not reliant on plenum temperature.
    AOP Rules: Rules For Equipment Owners.

    Free online load calculator: http://www.loadcalc.net/


    There = not here. Their = possessive pronoun. They're = they are
    It's = contraction of it is. Its = the possessive form of it
    Too = also. To = expressing motion. Two = 2
    Then = after that, next. Than = indicates a comparison.
    Questions should end with a question mark "?" Statements end with a period "."

  9. #9
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    At 30-35% do yo use any moisture on the windows? If it gets below 15 outside, if you don't have any it would not take much and you would. I guess the question is would a few % be worth the money?

  10. #10
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    you would never want a humidifier above the filter, especially an electronic as the water vapor would ruin it

  11. #11
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    Thread Starter
    Thanks for all the interest/questions. I'll try to answer each question to the best of my abilities. Any advice/insight is welcome.

    Quote Originally Posted by hvacvegas View Post
    Ive done it before.
    Only thing I would like to see is the bypass on both being as long as possible.
    Can you clarify? Do you mean you would want the bypass running anytime the fan is running? Right now, the system is designed so that the fan continues to run/circulate air for a few minutes after the primary heat source stops until the supply plenum temp drops to be more-or-less equal to the home temp (ie: no more heat in the heat-exchanger to extract by circulating the air). Would those extra few minutes really make that much of a difference?

    Quote Originally Posted by isuredo View Post
    you would never want a humidifier above the filter, especially an electronic as the water vapor would ruin it
    The electronic filter was tossed long before I bought the house, and is just using a washable filter. No one has ever pointed out the filter could be absorbing some of the humidity out of the air though. Given that the height of the filter matches more or less the top of the A-frame coil in the supply, from my understanding, I wouldn't be able to put a flow-through below the filter box. So that would mean that I would have to have the return modified, and have the filter box moved to the top?

    Quote Originally Posted by BNME8EZ View Post
    At 30-35% do yo use any moisture on the windows? If it gets below 15 outside, if you don't have any it would not take much and you would. I guess the question is would a few % be worth the money?
    When it gets cool (just below freezing -5C or so) there is a little mositure on the corners of the windows. But nothing very significant. I initially thought that would indicate that there is enough humidity in the house, but I have 2 different humidistats, and both read ~30/35%. And my skin is quite dry as well as I see wood floors/tables joints that separate which I attribute to the dryness in the air.


    Quote Originally Posted by kdean1 View Post
    X2
    Though, the humidifier will have a greatly reduced capacity when the heat pump is running because of lower plenum temperature. That's where the steam humidifier is superior because it is not reliant on plenum temperature.
    I have shied away from steam humidifiers for a couple of reasons. I was told they are more prone to causing mold/mildew buildup in the duct-work and have a much greater cost of ownership/maintenance, especially with the hard water I have in my area. Apparently the cost of replacing the evaporator coils in the steam humidifier are not insignificant, and with my hard water, it causes a lot of build-up limiting the efficiency of the unit. One thing I never checked is the current draw/electrical usage of a steam humidifier and if it is significantly more expensive to operate.


    Quote Originally Posted by pecmsg View Post
    iF A 12 gal cant keep up Id look at ways of tightening that envelope.
    By envelope, I presume you mean the house? At this point, I've done most of what I can in the last year(s) to tighten it without spray-foaming the whole house. At this point, all doors and windows are new (<10 yrs). All pot-lights in the attic ceiling have been sealed up with vapour barrier. But existing walls/attic/etc still have older blown insulate and Roxul in the walls. I would have to rip open all the walls and spray foam everything. Would love to; but it is cost prohibitive at the moment.


    Quote Originally Posted by pacnw View Post
    That would be an oddity!! Are you sure there is strip heat?
    Yes; it is a local system that supplements the heat pump by using electric strips in the plenums when the HeatPump is unable to meet the heat demands, in order to defer fossil fuel usage until -12C (when electricity costs jump 4-fold).


    Ideally, I'm looking to add humidity in the home without needing to make a huge financial investment. Hence the hope of upgrading to an 18gallon unit, hoping that it would be able to push more humidity in the air due to the larger filter surface area, but with that failing to fit, was wondering if I could use 2x 12gallon instead. I'm still confused as to why the tech told me that 2 units cannot run in parallel on the same duct though.

    Thanks!

    Eric

  12. #12
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    The 12 unit is it hooked to hot water?

  13. #13
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    Quote Originally Posted by pecmsg View Post
    The 12 unit is it hooked to hot water?
    No; cold water supply. I had asked that at time of install, but had been advised using hot water for different reasons. I never really validated the answers as they made sense to me at the time.

    • waste of hot water
    • hot water (from tank) contains impurities that would be injected into the air
    • hot water temp not high enough to make an impact on an evaporator pad


    Modifying the supply to the HW line would not be particularly difficult; is it worth making the change? Are the above issues not so critical?

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