Aprilaire Humidifier Not Sealed?

Discussion in 'HVAC Heating & Cooling' started by maccy, Nov 12, 2016.

  1. maccy

    maccy New Member

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    Hi there,

    We have an Aprilaire humidifier attached to the side of the furnace. I noticed that the utility closet where the furnace is located gets really hot compared to other rooms. I then noticed that warm air is blowing out of the side of the humidifier.

    This may sound like a dumb question but is it likely that the humidifier is not sealed?

    Thanks
     

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    Last edited: Nov 12, 2016
  2. cacher_chick

    cacher_chick Test, Don't Guess!

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    It might be helpful for us to see photos of your humidifier installation, so that we can better understand what is there to work with.
     
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  4. maccy

    maccy New Member

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    Ok uploaded a pic
     
  5. Reach4

    Reach4 Well-Known Member

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    Does your photo show the side that the air is blowing out of? That looks like an Aprilaire 700. The 700 does not seem to have a hole on either side. So where is the air coming out of?
     
  6. cacher_chick

    cacher_chick Test, Don't Guess!

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    The bypass duct should be connected to the port on the side of the unit, directing the humidified air back into the return side. It might be on the right side of the humidifier, but I cannot see that in your photo.
     
  7. maccy

    maccy New Member

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    Yes, it warm air blows out the left and top sided where the grey meets white
     

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  8. maccy

    maccy New Member

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    This is the right hand side of the humidifier
     

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  9. maccy

    maccy New Member

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    Between the grey plastic and white cover, the air comes out there
     
  10. Reach4

    Reach4 Well-Known Member

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    Is the top of the white cover locked in place? You should not be able to gently pry the white from the gray. I think there are top parts that engage before you snap the bottom part of the cover in place.

    Before you put the white cover on, the top of the black media holder pushes back into place with some force.
     
  11. maccy

    maccy New Member

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    There is a rectangular grey plastic part that connects directly to the furnace on that there is a white cover (with the Aprilairre logo on) that can be detached. The air comes out between the white cover and grey plastic meet on the left and top sides
     

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  12. maccy

    maccy New Member

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    It's clicked in place but it's easily detached so not tightly attached.
     
  13. cacher_chick

    cacher_chick Test, Don't Guess!

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    So what I said about the bypass is incorrect for your unit. your unit has in integrated fan that is supposed to blow inward through the pad when there is a call for humidity.

    It would not be unusual to get some air leakage at the seams. If there is any back-pressure in the heated air ducting caused by closed or blocked registers or dampers, the problem would be exacerbated.
     
  14. maccy

    maccy New Member

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    Thanks for responding, helped a great deal
     
  15. Dana

    Dana In the trades

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    It looks like NOTHING is really sealed on your ducts, and the connection to the humidifier probably leaks a ton too. All seams & joints of sheet metal ducts need duct mastic or (if clean & bright enough enough for an air-tight seal) purpose made aluminum tape over them. This is an easy (if sometimes messy) DIY job with duct mastic, using a small trowel or putty knive and some gloves and some clothes you might get rid of later. Sealing the ducts puts the air where it was designed to go, an usually improves overall efficiency, and makes the ducts quieter too. Don't forget to seal the register boots too, and caulk the seams where it hits the subflooring or wall/ceiling gypsum to prevent back pressure at the registers from pushing that air into framing cavities (or the great outdoors.)

    That said, humidifiers are almost universally a BAD idea, except in cases where it's necessary for particular medical needs. If the humidity levels in the house average 40% or higher during the cold winter months it raises the moisture level in the exterior sheathing & framing of the house, which then becomes an elevated mold-spore situation when the colder/wetter materials in the house warm up in spring, or even rot conditions on the structural sheathing. If your house is chronically under 30% RH in winter it's usually a sign of over-ventilation, air-handler driven air-infiltration, or a generally air-leaky house, and the solution is to fix it at the source, not by dumping humidity into the house.

    If your heating system takes in ventilation air whenever the air handler is running, reduce the amount or even eliminate the outdoor air feature- seal it up. If your house leaks a lot of air it's common to think of the weatherstripping at the windows & doors, but that's usually just the frost on the tip of the iceberg in a chronically winter-dry house. Just the seams of foundation sill and band joist is usually a bigger air leak than all the window & door crackage combined. Basement-to-attic plumbing, flue, or electrical chases often exceed the air leakage of the foundation sill & band joist. Upper floor ceiling and the basement are by far the most important areas to concentrate on, since those leaks define the height of the parasitic "stack effect" infiltration drives that run 24/365.

    Of course, unbalanced and leaky duct systems can create room-to-room pressure differences that drive infiltration whenever the air handler is running too, so getting that right helps too. Between the two most house can be cost-effectively (on reduced heating & cooling energy use) tightened to the point where dry wintertime air is no longer a problem.
     
  16. Dana

    Dana In the trades

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    Almost on cue this bit o' bloggery appeared on this morning's GBA site on how humidifiers are prone to reducing overall indoor air quality. (You can take a free trial membership to view it, since it's behind the pay wall. Full-disclosure: I have written blogs for that site in the past, but not this one. )

    An earlier blog on the topic by that same author lives here (no trial membership sign-up required.)

    Bottom line, the "right" thing to do with this type of humidifier is to politely decommission the thing, and spend some money on air sealing the house & ducts until you no longer have a dry air issue. In any Illinois climate that happens WELL before the house is so tight that active ventilation becomes necessary.
     
  17. Doctorman

    Doctorman New Member

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    So even in New york kind of weather a normal house will not need the humidifier in the cold of the winter?
    My HVAC guy did half A$$ job on sealing so I bought mastic and got to sealing all I could,
    The Aprilaire 700 is a bad design after having it installed on my supply side, there is now ay to stop the air leak from that device, we need it for 2 to 3 months to increase the humidity in the house the rest of the year it is just air leak in the supply side... the only way to seal that thing is to use whole lot of of duct tape at the end of season and take them off for winter...
     
  18. Dana

    Dana In the trades

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    That's right. If the house and ducts are reasonably well sealed and the duct design is reasonably well balanced, there would be no need for a humidifier unless an unusually high ventilation rate needed to be maintained. Sure, if this is a house full of smokers who burn incense, use plug-in "air fresheners" to keep the stink at bay you may need continuous mechanical ventilation at rates high enough that it would need humidifiers to keep it from dropping below 30% RH @ 70F indoors, even NYC.

    If the ducts are unbalanced creating large room-to-room pressure differences "the Great Outdoors" becomes part of the return path to relieve those pressure differences. Even in fairly tight houses high rates of air handler driven infiltration can occur if the ducts are unbalanced. Doored-off rooms that have only supply ducts, no returns are often big offenders, yet relatively easy to fix by creating adequate return paths (with transom grilles, jump ducts etc.)

    As a case in point- I live in a somewhat colder climate than NYC/Westchester/Long Island, in a location more comparable to Syracuse or Rochester. After tightening up the both the house and ducts (both circa 1923) the wintertime indoor humidity stays above 30% RH except after several days of extreme Polar Vortex cold snap sub zero F weather, and this is even with continuous active HRV ventilation covering parts of the house, and liberal use of exhaust venting in the bath/kitchen areas.

    I hope it is not installed in series with the supply plenum, with 100% of the supply air running through it(?). It's way too small and restrictive to be used that way in most systems, creating huge static pressure drops even with fairly small air handlers. Putting it in parallel with the filter & furnace with a take-off from a near-furnace supply duct (or the supply plenum), and installing it on the return plenum before the filter still moves enough air through it to provide the humidification function without causing high static pressures, which also increases leakage. If the return paths are constrictive (closed door, no dedicated return) the static pressures and leakage on the supply ducts increase, and more (potentially unhealthy) air gets sucked in to the return ducting, and the greater the room to room pressure differences become.

    An Energy Star duct system needs to have <3 pascals pressure difference between rooms under all air handler speeds, all conditions- doors open, doors closed. That's not too hard to hit if the returns are sized adequately, but impossible without a properly sized dedicated return path for every supply register in rooms that can be isolated by closing the door.

    Another big factor in air handler driven air infiltration stems from oversizing of the furnace or AC. Higher BTU/hr rates require higher cfm out of the air handler & ducts, inducing higher pressures. In NYC most central AC systems would have air handers in the 350-400 cfm/ton range to have reasonable latent cooling capacity, though it could easily be north of 500 cfm/ton. Typical hot air furnaces in the northeast are 3x or more oversized for the actual heating loads. Lower cfm yields lower duct velocity dramatically lowers the static pressure or "friction loss" in the ducts. A velocity of 600 feet per minute (pretty commonly designed in for hot air furnaces) creates 4x the amount of friction loss at 300 cfm. Where possible I personally recommend keeping duct velocities under 400 fpm, which keeps down the noise levels, and allows filter to work better at any MERV rating. Increasing the size of the return plenum to lower duct velocity to <300 fpm and installing large 4"-6" pleated filter media allows high MERV filters to be used without exceeding static pressure limits on the air handler. At <300fpm a MERV 13 filter performs almost like a HEPA filter.

    So, to mitigate against the need to run the humidifier to stay comfortable in winter take these steps:

    #1: Start by identifying and rectifying any return path issues on the duct system.

    #2: Do a serious round of air sealing on the house itself. If you're not a DIYer willing to get dirty in awkward places start by hiring an air sealing contractor that uses blower doors and infra-red imaging to find & fix the big leaks. Some of the big leaks are obvious and can be found & fixed without chasing it with equipment, but many big leaks are more subtle. A DIYer can do almost as well as the pros using a $200 FLIR One IR camera and a 16" reversible window fan, but it takes more time. The biggest less-obvious untreated (but easy to fix) air leak in most houses with basements or crawlspaces is the joint between the foundation & foundation sill, and the band joist. In most cases this leak exceeds all window & door crackage in the house combined, often by a few hundred percent (!).

    3: Figure out the oversizing factors of your equipment. Since it's the cooling season, measure the duty cycle of your AC condenser on afternoons that cross your 1% outside design temp. (About 88-90F in your area.) Take a look at this bit o' bloggery for ideas on how to go about it. If on afternoons when it's in the high 80s/low 90s outside it's running less than 50 minutes out of every hour ( a 60min/50 min= 1.2x oversize factor) the AC is suboptimally oversized for comfort. If it's running less than 40 minutes per hour (=1.5x oversized) it is high enough to be an efficiency problem.

    If you have some of last winter's heating bills, run the fuel-use against heating degree-day data from a nearby weather station to estimate the oversize factor of the furnace as outlined in this other bit o' bloggery. Be sure to use winter-time fuel bills only (to reduce the errors from solar gain and other uses of the same fuel.) If you can share the fill up or meter reading dates & amounts (gallons or therms, not dollars) and the nameplate BTU-in/DOE-out of the furnace I can run those numbers for you here on the forum.

    If it turns out you can replace a system with a 1500-2000cfm air handler (~80-100KBTU furnace, 3.5-5 tons of AC) with an 800-1200 cfm air handler (35-50,000 BTU/hr heating, 2-3 tons AC) you'll end up with longer, more comfortable run times, but also with dramatically less air handler driven infiltration, and higher wintertime indoor humidity. While it's not necessarily going to be economic to replace the oversized equipment on an energy cost basis, it's sometimes necessary to make the house truly comfortable. See the short videos linked to on these pages:

    Home Comfort 101

    HVAC 101

    HVAC 102
     
    Last edited: May 26, 2021
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