As we unfortunately move into another wildfire season, we would like to remind readers of steps to be taken to minimize smoke and other particulate concentrations in your home. High on the list of things to do is to positively pressurized your home and to recirculate indoor air through a high quality MERV13 or better filter. Things you should not do is negatively pressuring your home through the use of exhaust vent operation (kitchen hoods, bathroom exhaust, clothes dryer exhaust, gas water heater flues, external air combustion furnaces, etc).
The Atlantic article linked above, as in most articles on smoke, recommends closing windows and recirculating indoor air through a filter, however, the article forgets that occupants need to add fresh air, too! Read our newsletter article from last summer to refresh yourself on active steps you can take to reduce particulate density in your home while maintaining healthy levels of CO2 and VOCs.
Particle concentrations are more easily maintained in smaller, well-sealed homes, but the steps we have outlined are important for all homes. In addition to sealing a home and recirculating indoor air through a MERV13 and higher filter, positively pressuring your home is essential. Operating a balanced (neutral pressure) ventilation system means that half of your home’s leakage pathways are particle ladened infiltration leaks and the other half are exfiltration leaks. Positive pressure operation converts infiltration leakage paths into exfiltration paths, creating a barrier against particulate infiltration. Ideally, all leakage paths become exfiltration paths, blocking particle ladened infiltration.
For CERV2 owners, positive pressure operation is a simple menu selection to offset fresh air supply fan and exhaust fan speeds (increase supply fan relative to exhaust fan speed). CERV2 smart pollutant sensors also reduce outdoor particulate inflow because the CERV2 only brings in fresh air when needed. When fresh air is not needed, the CERV2 operates in whole house air recirculation and filtration mode. Recirculation is important for filtration of particulates, and for making use of fresh air “stored” in unoccupied areas of a home. This smart usage of fresh air further minimizes the CERV2’s need to bring in outdoor air.
Without a CERV2, one can pressurize their home by sealing a box fan with filters into a window. Two layers of filter on the fan’s outside face are good. One should be a MERV13 or higher and the second layer could be an activated carbon filter. in a window, with air blowing into the house.
Using a good quality indoor air monitor that registers CO2, VOC and PM2.5 particulates will help you determine the best combination for operating the pressurizing fan. We recommend keeping indoor CO2 at 800ppm as a primary control point. Because elevated outdoor VOCs often accompany smoke, carbon filters help absorb and reduce VOC concentrations. If you’re able to connect a control relay activated by the IAQ monitor, the pressurizing fan could be modulated by the monitor’s CO2 setting, otherwise, observing indoor CO2, and manually turning the pressurizing fan off/on can be used. A CO2 “deadband” of 200 to 400ppm (that is, turn fan on when CO2 exceeds ~1000 to 1200ppm, and turn fan off when CO2 drops to 800ppm) is reasonable.
A third of North American homes have someone with respiratory difficulties…asthma, allergies, COPD, etc. We hope this guidance helps keep your air healthy and your comfort high.
