Impact of Whole-Home Dehumidification and Filtration Systems on Levels of Relative Humidity, Particulate Matter and Indoor Allergens in Low-Income Homes: Results from the Healthy Homes Study

BACKGROUND: Relative humidity (RH) >50% has been linked to increased levels of dust mite allergens; exposure to these allergens along with other indoor pollutants is associated with increased asthma morbidity. Current home construction standards have improved energy efficiency but increased levels of RH and air pollutants. METHODS: We examined how high-performance housing retrofits, designed to decrease humidity levels and increase air filtration, affected the levels of RH, particulate matter (PM), and indoor allergens in 22 homes. Enrolled homes were randomized to either intervention or control. Intervention homes received installation of the following: mechanical dehumidification, closed crawl space, high performance exhaust ventilation and upgraded HVAC filtration. Indoor and crawl space RH were logged every 15 minutes. Questionnaires were administered, and dust and air samples were collected seasonally over 12 months of follow-up. RESULTS: Indoor RH was significantly lower in intervention versus control homes, as determined by the percentage of time RH was above 50%; mean(SD) 24.2%(18.7) vs. 46.8%(18.4), (p<0.01). Dust mite allergen was detected in 70% of homes; however, there was no difference in allergen levels between intervention and control homes. Levels of PM₁₀ and PM_2.5 were reduced in intervention versus control homes; GM: 4.7 vs. 6.8, (p<0.02) and 4.7 vs. 5.4, (p=0.34), respectively. CONCLUSIONS: Whole-home dehumidification reduced RH; however, this reduction was not correlated with a decrease in dust mite allergen. Improved ventilation and filtration led to reduced PM with the greater reduction in PM₁₀ likely due to the increased efficiency of the upgraded HVAC filter at removing particles >3µm.