In residences without forced-air mechanical ventilation, maintain the minimum outdoor air ventilation rate recommended in Table 2.3 of ASHRAE Standard 62-1989. Dehumidification or supplemental ventilation (air conditioning) may be required to maintain thermal environmental conditions specified in ASHRAE Standard 55-1992 (ASHRAE, 1993).

Commercial Buildings

A number of principles and practices can be employed for controlling indoor allergens in commercial buildings, as outlined below:

  1. Outdoor air intakes should be located at a site (preferably on the roof) where the ambient air quality is the best. Grade-level sites should be avoided. Outdoor air inlets should be located at sites so that possible entrainment of contaminants from cooling towers, exhaust and relief vents, and other contaminant sources is avoided. Keep the outdoor air intake plenums clean.

  2. HVAC systems should be accessible for cleaning. Ceiling AHUs, rooftop AHUs, and central system AHUs must be designed for easy access for cleaning. Access panels should have gaskets and smooth inner surfaces.

  3. Filter banks should be changed frequently and kept dry.

  4. Avoid stagnant water in the heat exchangers of HVAC systems; drain pans should self-drain. Biocides that can be aerosolized into indoor air should not be used in operating AHUs (drain pans), water spray systems, and humidifiers.

  5. Keep the porous insulation in HVAC systems clean (by protecting with adequate filtration) and dry. If the insulation is contaminated, consider cleaning it with a HEPA filter vacuum, replacing the insulation, externalizing the insulation, or placing the insulation between metal surfaces.

  6. Avoid the use of materials that cannot be cleaned in common return air plenums; avoid the use of cellulose; avoid the use of high-surface-area materials. Do not locate air-handling units in a common return air plenum.

  7. Peripheral HVAC systems should be accessible for periodic maintenance. These units should not be used in buildings if maintenance is impossible.


The fundamental objectives of environmental control are to prevent or minimize occupant exposures that can be deleterious and to provide for the comfort and well-being of the occupants. Well-designed and maintained HVAC systems will exclude most aeroallergens (e.g., pollen, fungal spores) from interior spaces. Poorly designed or maintained systems, however, can

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