RE: new member, mold in crawl space and furnace

[Guest guest]

Rhonda,

Your letter describes two problems, which may or may not be related, both

potentially causing adverse health effects. Standing water in crawl spaces

is a definite problem. Unless your home is at the bottom of a low lying

area, you may be able to have drains installed to a lower part of your

property. A vapor barrier may help with vapor coming up from the ground, but

unless the liquid water is drained out, the vapor barrier may be

ineffective. This crawl space mold might also be causing the odor under your

sink, coming through the floor around the drain pipe.

The HVAC is another matter. Having developed respiratory problems from the

moldy HVAC at my former workplace, leading to my early retirement, I have

read up much on this topic. A twelve year old house is likely to have a

furnace with a fiberglass ductboard plenum. When first developed, these

seemed ideal. They muffled fan noise and they were easy for installers to

work with, eliminating the common hand and finger cuts associated with

working with sharp sheet metal for the plenums. Plus, they were better

insulators than sheet metal, leading to better energy efficiency. Some

contractors liked the look of sheet metal, but installed insulation inside

to improve energy efficiency. Both systems are problems waiting to arise.

Fiberglass ductboard and fibrous insulation both trap dust, including mold

spores and bacteria. In cooling season, air passes through air conditioner

coils, where it is cooled below its dew point, causing water to condense on

the coils and flow out a drain. But, because of the velocity of air flow

over these coils, some water is aerosolized from the coils and is trapped in

the ductboard or insulation. Early in the morning, when the AC isn't

running, the temperature inside that wet dusty plenum warms a little,

getting close to ideal mold/bacteria growth conditions. Similar conditions

occur in winter if a furnace humidifier is used. The solution, as Carl

alluded to is to remove this ductboard or interior insulation, and replace

the plenum with sheet metal, with insulation wrapping the exterior.

But even a properly configured air conditioner can get enough dust

(nutrient) inside to grow mold, possibly even enough to clog the drain and

make the drain pan overflow. Therefore, it is a good idea to have the coils

and pan cleaned periodically, disinfected with dilute Clorox, and perhaps

put a slow release chlorine disinfectant in the drain pan. Also important is

to use good filters, such as 3M Filtretes, to prevent the dust from getting

into the coils and drain pan in the first place.

A third consideration is your return air supply route. Does this go

through the crawl space? If it does, any holes in the ducts can be sucking

moldy air from that crawl space. Pipe with large holes should be replaced.

Small holes and all seams should be sealed with professional grade duct

tape. Dirty flex duct should