Mildew on mastic @ plenum 10 month home

Is it common to start seeing mildew on such a new home? I’ve seen it time and again on older homes but what could cause such staining on a 10 month old home? Lack of filter changing??


But common this early on?

If the duct is insulated, could be a gap in insulation allowing cooling /condensation at the seam.

Mildew (mold) doesn’t know (or cares) how old the home is. If conditions are right it can form in a matter of a day or two (36 hrs in one article I read recently).

New homes are loaded with moisture and can take years for to balance .
Wet cement green lumber .
Drywall gets painted and with the paint sealing it to can take a long time to loose all its moisture .
A dehumidifier set below 50% will help big time and have it drain with a hose .

It is not likely that you can prevent mold on this appliance (regardless of where it is located) when condensation can form on the air duct with a relative humidity is low as 12%.

Moisture + humidity (at the correct levels) = mildew

[size=2]This is a fiberglass duct board connection which seldom has an adequate seal to the equipment. (One of the drawbacks for this application)


We don’t have that material in my area (or I haven’t seen it yet)…all metal. When I looked at the picture, could not tell if it was metal or not.

Would make sense then that a bad cut of the material and/or a poor connection with even a small gap between duct ends would cool the mastic leading to what’s seen in the picture.

Yup, basically this duct is taped to the unit from the outside, allowing conditioned air directly against the mastic.

In looser, new homes from pre-1975, it usually took 18 months or so for the bulk of moisture to leave the home. Then the home would go through the usual seasonal uptake/and then release of moisture from summer through to winter/spring.

With well designed/installed HRV’s/air exchangers, the bulk of moisture could be removed from the home within 2-3 months. In 1987-8, a couple of the HRV manufacturers added extra low speed controls to their units so houses would not be overdried in Jan/Feb.

We see this on a daily basis. Typically what it is (and by the pictures) where the insulation board meets with the plenum, there is a gap and causing the cold air to escpape, thus creating a cold seam. It LOOKS as though this is in an attic area. Depending on the humidity and temperature it may only take a few degrees differential to reach dew point. Yous tart reaching dew point, you start making condensation and then you start making mold. The uniformity appears to be a compromise where the ductboard meets the plenum. Easy fix, have the HVAC technician come back and ensure the seam is insulated to prevent cold air from leaking out at the seams. This usually takes care of it.

Don’t wast your time and money on an HVAC guy (Russell is just trying to help Obama stimulate jobs), that is not leaking.

It is a thermal bridge not a thermal bypass.

If you really want to know, spend $30k on IR…