Healthy Indoors Magazine
Issue link: https://hi.healthyindoors.com/i/1088111
Healthy Indoors | 37 Air Handler/Furnace Insulation: Where needed for sound control, return plenums as well as blower-cabinet access panels should be insulated with closed-cell foam or with aluminum-foil covered fibrous lin- ing material. Supply plenums can also be insulated with alu- minum-foil coated fiberglass or closed-cell foam. Lining with exposed fibrous material should never be present anywhere in a ducted system! Filtration: I always recommend a pleated-media filter with a MERV rating of at least 8, though for families with allergies or asthma, a MERV rating of 11 is preferable. The filter holder should be located at the air handler and be airtight. A coarse fiberglass "furnace" filter can be installed in a ceiling return grille as a pre-filter to help keep the return duct clean. Any filter should be readily accessible. The most important function of the filter is to keep the heat- ing and cooling components dust free. This purpose is not sexy enough for many filter sales people so they sell the filters to make the indoor air healthier. Ultra-violet lamps: The sales pitch for UV lamps is that they will disinfect the air. In order to kill some microorganism, however, the organism must be irradiated for at least a min- ute. Since air is traveling through a duct at several feet per second, this means installing a UV lamp several hundred feet long in a duct! Commercial installations of UV lamps that fully irradiate cooling coils can be very effective in disinfecting the coil (but not the air!), but the typical residential UV installation is useless because the lamp is too small. In addition, the UV lamps may create ozone: one of the irritating gases in smog. Excellent filtration is a better way to go. Separate Heating and Cooling Systems If the house in a temperature zone with cold winters has a central air-conditioning system in the attic (with a sepa- rate hot-water or steam heating system), future occupants should be instructed to close all A/C supplies in the winter and to cover return grilles. This will go a long way in pre- venting moist house air from migrating into the ducts and fueling mold growth. (I have seen water dripping out of an attic-mounted return boot near a kitchen in winter.) Using a Mechanical System during Construction A ducted system should not be used during construction or renovation. Supply and return ducts should be closed and cov- ered. Radiators and baseboard convectors in the work area should also be covered during renovation projects to prevent the collection of biodegradable dust. If needed, portable heat- ing and/or cooling units can be used while work is on-going. Soiled pan bay May Indoor Air Investigations LLC I generally don't like to see basement supplies, because they can pressurize the basement and force moldy base- ment air up into habitable rooms. In the winter when the blower shuts down, residual warm air flows out of supplies upstairs and passively draws in basement air. In either case, if the basement contains mold growth, mold spores will be carried into spaces above-grade. In the home of one man with mold allergies, just sealing off the basement sup- ply stopped his allergy symptoms in the bedroom upstairs. Leaky return ducts in basements and crawl spaces can also entrain mold spores. Insulation: Do not insulate ducts on the inside with ex- posed fibrous lining material, as this material collects biode- gradable dust and can never be adequately cleaned. Exposed fibrous lining material full of biodegradable dust and mold growth May Indoor Air Investigations LLC