Implications for Good Building Practices
Particle filtration technologies are well established and widely available. Currently, most building HVAC systems include filters with a relatively low efficiency rating. For example, U.S. commercial buildings often use filters with a Minimum Efficiency Reporting Value (MERV) of 7, with a low efficiency in removing the small particles most important to health. The filters used in the HVAC systems of houses often have an even lower efficiency. The incremental costs of using higher efficiency filters, e.g., those with a MERV 11 rating, are modest — less than a U.S. dollar per person per month [11, 62] and the predicted health benefits are substantial. Consequently, routine use of higher efficiency filters in HVAC systems represents a good building practice. Stand-alone fan filter systems may also be employed to reduce indoor particle concentrations, particularly in homes of people with allergies or asthma and containing pets or other strong sources of airborne allergens. The energy consumption of fan filter systems varies widely. Energy efficient units, sometimes with very efficient brushless direct current fan motors, will cost less to operate and are preferable when considering the impacts of energy use on climate change.
At present, given the limited evidence of health benefits, none of air cleaning technologies other than particle filtration can be recommended for broad use. For gas phase air cleaners, not enough is known about long term performance of reasonable cost systems, and health benefits have not been demonstrated. Air cleaners that generate significant ozone (see the supporting information) should be avoided. The health benefits of UVGI systems in buildings that are not health care facilities remain uncertain.