A significant research report published in April of this year by the National Center for Healthy Housing (NCHH) found that subsidized multifamily housing with ASHRAE 62.2-compliant ventilation had better indoor air quality than housing without 62.2-compliant ventilation. This important research states: “Levels of four of the five indoor contaminants improved substantially with [continuous] mechanical ventilation.”1 See Table 1.
The study was conducted in 152 multifamily dwelling units in Chicago and New York City between 2018 and 2020. The researchers tested dwelling units with ASHRAE 62.2-compliant ventilation (study group) compared with units without 62.2-compliant ventilation (comparison group). Both groups had been rehabilitated using green building practices.2
The contaminants measured over an eight-month period included:
- Nitrogen dioxide (NO2)
- Particulate matter 2.5 micrometers or less in diameter (PM5)
- Carbon dioxide (CO2)
- Carbon monoxide (CO)
- Formaldehyde
Nicotine was measured in order to control for effects of smoking during the study.
“All homes in the study group contained, by design, bathroom mechanical exhaust ventilation that operated either continuously or on a timed intermittent schedule [and] some study group homes also had continuous kitchen mechanical exhaust ventilation ducted to the exterior.” All of the dwelling units in both the study and comparison groups had a working gas-fueled kitchen range.
The study’s conclusions were:
- Continuous mechanical exhaust-only ventilation in bathrooms reduced four of five contaminants (all but nitrogen dioxide, probably because of indoor air chemical reactions and outdoor influences)
- Effective air exchange rates (ACH) were higher in dwellings with continuous mechanical ventilation than those without
- Continuously operating bathroom exhaust ventilation was likely the cause of improved PM5 and CO2 levels, probably because this ventilation effectively served the entire dwelling
- CO and formaldehyde were lower with continuous kitchen exhaust ventilation ducted to the outdoors. See Table 2.
Table 2. Two contaminants studied that were produced by gas-fired kitchen ranges were less in the Study Groups than in the Comparison Groups because of mechanical kitchen exhaust ventilation. [GM = geometric mean; ppb = parts per million; μg/m3 = micrograms per cubic meter]
The major recommendations of the study included:
- Install ASHRAE 62.2 ventilation3
- Provide financing for financing ventilation installation
- Simplify the ASHRAE 62.2 Standard in order to increase compliance
- Replace gas ranges with electric ranges
- Adopt smoking-free housing policies
- Improve maintenance of ventilation equipment
- Educate occupants regarding the use of mechanical ventilation
An interesting finding for the low-income weatherization program was that continuously-operating bathroom exhaust ventilation was instrumental in improving IAQ in these multifamily dwellings. This type of double-duty ventilation (one exhaust fan providing both local ventilation for the bathroom AND whole-house ventilation) is often installed in weatherized dwellings in order to lower installation costs. The results of this research support the viability of this common practice.
Studying the Optimal Ventilation for Environmental Indoor Air Quality is a 167-page report available from the National Center for Healthy Housing (NCHH).4
References
1 ASHRAE 62.2 is titled Ventilation and Acceptable Indoor Air Quality in Residential Buildings. This free 62.2-compliant RED tool sizes dwelling-unit ventilation.
2 The National Center for Healthy Housing (NCHH) defines a healthy home being characterized as being, properly ventilated, dry, clean, free of pests, free of injury hazards, without chemical contaminants, maintained, thermally controlled, accessible, and affordable.
3 ASHRAE 62.2 is titled Ventilation and Acceptable Indoor Air Quality in Residential Buildings.
4 The National Center for Healthy Housing (NCHH) defines a healthy home being characterized as being, properly ventilated, dry, clean, free of pests, free of injury hazards, without chemical contaminants, maintained, thermally controlled, accessible, and affordable.
