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  1. #1
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    Confused Air handler closet full of mold

    We had a new Lennox system installed Mar 2015, new blown-in insulation done in attic, energy audits, the whole ball of wax (and spent a wad). Everything has been fine and they've done two checks seasonally since installation. My husb maintains filters. This weekend, for the first time in months, I opened the hall closet where the air handler is (the old louvers on it were covered over with insulating foil for the energy audit) to find a sweating unit and both side walls in **full mold bloom**. Shining flashlight around in there, my husb noted that this closet had been left open to attic above with the new installation, a fact that had escaped his notice before. It's a veritable mold factory, with constant moisture, Texas heat above, and no air circulation. Their tech was last out about two months ago for a seasonal check and didn't report anything amiss. If mold really wasn't there then, it was grown fast.

    What is best way for them to address this now? I'm clueless, but this seems like a real dropped ball on their part. I've read around on forums and the issue with these new energy effic unit seems to be how they must be ventilated, components' proximity to one another, whether fan on ON or AUTO, but can someone explain the basic issues here in layman's terms? And is this common? We don't want to freak out b'c it's mold, but it's a LOT of mold, and this was a pricey upgrade for us, only to have this kind of awful problem now.

    I'll post unit specs in a bit, waiting for my husb to send me these, but want to have some language & some ideas in order to talk to the company about this when they come.

    Thanks.
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  2. #2
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    Here is the unit model: Lennox XC17 single stage. House is 1950s era, approx 1750 sq ft. The fancy inside "smart" thermostat rarely shows indoor humidity above 46%.

  3. #3
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    is this gas heat? return below?
    take a few steps back & take larger area pic.
    show the top of the closet
    mid ways of the closet
    the platform & bottom of the unit.
    then take a pic of the return air.
    just for fun...show us what the energy auditors
    installed on the back of the door.

    the open to the attic is the main cause...but
    is this electric heat or gas? makes a difference
    in how to address your issues.
    where the plenum meets the equipment...is there
    access on sides & to back?

    more info needed.

    best of luck
    The cure of the part should not be attempted without the cure of the whole. ~Plato

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  5. #4
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    Thanks, here are pics hope they show what you need. It's gas heat and the return is below. Louvers were covered with foil insulating sheets. It's pretty tight in the closet, not sure of clearance on back side but on sides just a few inches.
    Attached Images Attached Images      

  6. #5
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    So they came today and scrubbed the mold off the drywall with my cleaning supplies (they brought none), and cut thick foil-backed insulation to plug up the opening to the attic, more or less. (Less, in my opinion.) There are those huge metal ducts hanging down in the front of the closet, which you can see in pics, that are necessary to ventilate the gas or something? That all looks pretty jerry-rigged to me, but they say it's "to code." And it's impossible to easily plug up the gaps around them but those are sort of stuffed with extra insulation material in the two biggest gaps. Not much assurance that this will address the heat prob, which is causing the moisture prob, which is causing the mold prob. Very disappt'd, but don't have enough info to argue the fix with them. Am still debating removing the foil insulation on the door louvers, as old fashioned common sense would say a little ventilation in there might help with the mold, but we are far from being totally sealed off from attic heat. Tech sugg'd if I only take off one, make it the lower one as air coming in there will better circulate (my theory was heat rises). We plan to paint the drywall with a fungicidal paint (Zinssler?) and maybe if we hop on one foot and say a prayer mold won't regrow? Would love another professional opinion.

  7. #6
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    Rule number one about mold: no water, no mold.


    You should not need to uncover the louvered doors to solve this problem (which may not solve the mold concern, anyway).

    Most of the time what causes mold to grow in a mechanical closet like this (my house is the same way: louvered doors that are covered up on purpose, ceiling with openings to the attic for combustion air, and furnace drawing air into it from a pocket underneath with grills in the hallway) is cold air from the a/c leaking out of the supply plenum and blowing against the drywall. This air cools the drywall, and when warm, moist air from the attic mixes in with the cold air and cold drywall, the drywall gets moist.

    Remember Rule Number One about mold, stated above. To keep mold away you must keep water away, and to keep water away in that closet you must keep the walls from getting cold. Check for air leaks in the closet when the a/c is on and blowing cold.
    Psychrometrics: the very foundation of HVAC. A comfort troubleshooter's best friend.

  8. #7
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    Quote Originally Posted by Shophound View Post


    Rule number one about mold: no water, no mold.


    You should not need to uncover the louvered doors to solve this problem (which may not solve the mold concern, anyway).

    Most of the time what causes mold to grow in a mechanical closet like this (my house is the same way: louvered doors that are covered up on purpose, ceiling with openings to the attic for combustion air, and furnace drawing air into it from a pocket underneath with grills in the hallway) is cold air from the a/c leaking out of the supply plenum and blowing against the drywall. This air cools the drywall, and when warm, moist air from the attic mixes in with the cold air and cold drywall, the drywall gets moist.

    Remember Rule Number One about mold, stated above. To keep mold away you must keep water away, and to keep water away in that closet you must keep the walls from getting cold. Check for air leaks in the closet when the a/c is on and blowing cold.
    Thanks

    Other than holding your hand up to the plenum and FEELING for leaks, is there some surer test? I would think they'd have checked that and they didn't report it was leaking, but they def'ly felt the addt'l bits of insulation against attic heat would help the sweating problem. I just spent an hour standing in the closet door opening, painting the walls with fungicidal paint. I'm considering taking the lower louver cover off, b'c the sweating of the system has been minimal since I've had the door open painting. Bad idea?

  9. #8
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    Quote Originally Posted by Luckywest View Post
    Thanks

    Other than holding your hand up to the plenum and FEELING for leaks, is there some surer test? I would think they'd have checked that and they didn't report it was leaking, but they def'ly felt the addt'l bits of insulation against attic heat would help the sweating problem. I just spent an hour standing in the closet door opening, painting the walls with fungicidal paint. I'm considering taking the lower louver cover off, b'c the sweating of the system has been minimal since I've had the door open painting. Bad idea?
    You mentioned sweating. Is the air handler/furnace or ducting attached to the furnace itself sweating? If so, here's another theory: the cold surfaces that are sweating, if on the furnace, are cooling the walls nearby to where they are near or at dew point. When a surface like an interior wall nears dew point, it's ripe for mold growth, being what it's made from and has applied to it (paper, water based latex paints, etc.).

    Bottom line: you could have no apparent cold air leaks in this region but still have a potential mold factory because cold surfaces on the furnace are cooling the nearby walls via radiant cooling.

    I do not recommend removing the covers over the door louvers, as they were put there to separate house air from attic air. With the two duct tubes extending down from the attic to provide combustion air to the furnace, that closet is still connected to the attic, air-wise. You need to get the sweating stopped, and that should stop any potential for future mold growth.
    Psychrometrics: the very foundation of HVAC. A comfort troubleshooter's best friend.

  10. #9
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    It's just the plenum that's sweating where it attaches to the unit, but I can't see any ductwork, it's all in the attic with blown in insulation around (done by same company at same time). The first few inches above where plenum connects with mastic to the metal housing is cold and sweating all around when the system is running; up just a couple inches higher it's warm and dry. The drywall walls are just inches away on either side.

    So HOW to stop the sweating? Is this a matter of just trial and experiment? Techs felt the little bit of insulation they put in closet top today would "help" but even they didn't say for sure. And as you point out, those vent tubes hanging there bring continuous heat from attic.

    They cleaned up with Borax all the mold they could reach, and I just painted the walls with Zinsser Mold Killing Primer. Even if that paint actually keeps mold from forming, it's still the case that there is too much condensation and it's going to cause some kind of problem, perhaps even rusting out this $$$ system? These all seem like bandaids, and trying to get AC techs to take a considered approach to fixing the problem long term is a losing proposition in Texas in summer, as they have bigger fish to fry than the high dollar system they sold us last year.

  11. #10
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    You stop sweating on a surface by raising its surface temperature above the dew point temperature of the air surrounding the surface. This can be achieved by insulation with a vapor barrier covering the offending surface.

    In your closet you may have a combination of air leakage and cold surfaces on the plenum cooling adjacent walls to where they can grow mold. That closet makes for a tight install and unless the installers sealed the back of the plenum with mastic before scooting the furnace in place, it's leaking cold air back there.

    If you had an infrared camera like a Flir One you could point it at the system after it has been running awhile and see where the cold spots on the wall are, as well as where the cold spots on the plenum. That said, the sweating is already telling you something. You're losing cooling capacity to the house in addition to creating an environment favorable for moldy wall surfaces if there is sweating surfaces near the walls.
    Psychrometrics: the very foundation of HVAC. A comfort troubleshooter's best friend.

  12. #11
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    You stated that the plenum sweats where it attaches to evaporator coil. The best I can tell there is access if the flue pipe is removed. Have them open the plenum and make sure this area is insulated and sealed. Even the back of the plenum could be sealed from the inside. What part of Texas are you located?

  13. #12
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    Quote Originally Posted by Shophound View Post
    You stop sweating on a surface by raising its surface temperature above the dew point temperature of the air surrounding the surface. This can be achieved by insulation with a vapor barrier covering the offending surface.

    In your closet you may have a combination of air leakage and cold surfaces on the plenum cooling adjacent walls to where they can grow mold. That closet makes for a tight install and unless the installers sealed the back of the plenum with mastic before scooting the furnace in place, it's leaking cold air back there.

    If you had an infrared camera like a Flir One you could point it at the system after it has been running awhile and see where the cold spots on the wall are, as well as where the cold spots on the plenum. That said, the sweating is already telling you something. You're losing cooling capacity to the house in addition to creating an environment favorable for moldy wall surfaces if there is sweating surfaces near the walls.
    Thanks, this all makes sense, but we'll have to either get them on board with this, or find another HVAC person to check it out. They say it's as well sealed as can be, but it all looks pretty shoddy to me, lots of gaps, and the existence of that flexible metal vent pipe dangling down into the closet letting attic air in....can we just seal that up as long as it's not winter and we're not using the gas heat?? Our old system didn't have anything like that, and it's clearly a bit part of the humidity equation.

  14. #13
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    Do not seal those tubes up. That is not the source of the problem; only a bit player.

    Do you live in the DFW area? If so I know some folks who can likely fix this problem.

    Also remember Rule Number One: no water, no mold. Cold surfaces attract water. Where there is mold, there is or has been water.
    Psychrometrics: the very foundation of HVAC. A comfort troubleshooter's best friend.

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