Healthy filters: Prep your home now for better indoor air quality if wildfire smoke lurks outside

In recent summers, wildfire smoke has blanketed the region. Residents can take steps now to prevent contaminants from affecting indoor air quality, said a Pullman researcher.

Even without smoke, indoor air quality in many homes is worse than outside air, said Max Kirk, professor emeritus in building science at Washington State University. He and a research team did a study on indoor air quality and wildfire smoke impacts published in 2018.

“Indoor air is three to five times worse than outside air,” Kirk said. “So, during a wildfire smoke event, it is important to prevent that outside air from getting inside.”

Factors affecting indoor air quality include fine particulate matter, released ozone and impacts from products “off-gassing,” such as formaldehyde released in small amounts from flooring and furniture. Modern homes don’t “breathe” as much as older structures, he said, thanks to building codes for energy efficiency and tighter construction to reduce air leaks.

Outside air does get in, though, when doors and windows are opened, as well as from any cracks or gaps.

“We’re getting into smoke season, so there are things people can do now for their homes’ indoor air quality,” Kirk added. “I think this year, we’re going to get hammered.”

The health concern from smoke comes from breathing in contaminants that are in fine particles, when the air quality index rises to the warnings of orange to maroon. That’s also when people are advised to stay indoors as much as possible with closed doors and windows.

The finer the particles, the unhealthier the smoke becomes and can aggravate heart and lung diseases. “We call them particulate matter or PM, categorized as PM 10 and PM 2.5, which are represented in micrometers,” Kirk said. “A micrometer is too small to be seen without a microscope, and when there are many of these fine particles, we see them as smoke.

“During a smoke event, going inside is safer than outside, and if they shut all the doors and windows, they should be fine.” But among tips to protect indoor air now, Kirk said residents can check whether it’s time to have a forced air system maintained by a professional if they have such a unit. Kirk suggests getting units serviced once a year.

If there’s a smoke event, people who have forced air units then should put them on recirculate – either with the air conditioning on or off. Another consideration is the quality of the filter for the unit, he said. “Make sure you have a filter for the system that will filter the air in the house for fine particles,” he said.

“Your normal filter you buy isn’t for humans, it’s for the furnace itself to keep dust and stuff out of the furnace, but there are filters for humans and for filtering the smoke that may get in your home, and it starts with a Minimum Efficiency Reporting Value or a minimum MERV 10. Check on MERV information at the EPA’s website epa.gov/indoor-air-quality-iaq/what-merv-rating-1.

However, be sure to check – perhaps with a technician who services your unit – whether a furnace can handle that type of filter, he said. Filters with too much resistance will not allow the blower fan to push the air through the filter, meaning a forced air system won’t function as designed. “Use the highest MERV that the blower fan in your furnace can allow,” Kirk said.

A minimum rating needed for filtering smoke is that MERV 10, which will filter 50% of particles that are 1-3 microns. The rating information is sometimes listed on the filter’s packaging, but home owners might need to check with a service company or on a manufacturer’s website.

Kirk also is concerned about misinformation on the proper mask to wear if you’re outside in bad smoke conditions. “If they have to go out and the smoke gets to a dangerous level, depending on health concerns and if they have asthma or heart conditions, they should wear a mask, and that mask isn’t the same as what we talked about before with COVID.”

Kirk said there is only one type of mask recommended for protection from smoke, the N95 or KN95 mask with or without valves. Other masks, such as surgical or homemade masks, will not filter wildfire smoke. During a wildfire, the mask protects the user. That’s as opposed to the reason cited for a mask during the COVID-19 pandemic, in which “the purpose of the mask is not protect the mask user, rather it’s to protect the people around the user,” Kirk said.

An N95 mask filters down to 0.3 microns. A valve simply makes it easier to breathe out, he said, but still filters particulates from being inhaled. “With smoke, we can have the valve because what we want is to breathe out; we just don’t want the smoke into our system. A cloth mask isn’t tight enough nor does it filter.”

As another tip for the home, consider a standalone air purifier with a high-efficiency particulate air filter – if you can afford one, Kirk said. “If they don’t have forced air, I’d suggest getting an in-house air cleaner, and if they can, one with a HEPA filter. Put one in at least a bedroom; you’re stuck in that room for a good eight hours.”

Kirk said people don’t need to purchase an air cleaner that has an ultraviolet lamp because a UV lamp will have no effect on smoke particles. If there’s some smoke detectable indoors, especially among those with health conditions, they might consider wearing an N95 even while home. “A N95 mask is cheaper than an air purifier,” he said. He detailed other steps if there is wildfire smoke:

• If you can’t afford an indoor air cleaner, use a box fan and attach a store-bought filter. Make sure the filter thickness does not prohibit the air flow through the filter. If the filter is too thick, it can cause the fan motor to overheat.

• Make sure the filter box fits tight and seals around a filter. Many older furnace systems that hold filters leak air around the filter, making them ineffective.

• If you have a heat recovery unit attached to your forced air system, turn the system off during the worst of the smoke event.

• If your home has a make-up air system, turn the system off during the worst part of the smoke event. Without a forced air system, remember that older homes have an ability to self-filter out smoke to a certain extent, Kirk said.