That includes UV products, air purifiers, and air filters — the latter of which, by its nature, has the characteristic of getting dirtier as the air gets cleaner.

“It is the job of the filter to catch things in the air,” said Duke Wiser, president of Dynamic Air Quality Solutions. “Coronavirus can be airborne. If there [are coronavirus particles] in the air in the house or building (i.e. if someone in the home is already infected), there is a good chance it will wind up on a filter media.”

Proper protocol, therefore, becomes incumbent upon HVAC technicians to protect both their health and the health of the customer while working with air filters that are definitely dirty and possibly contaminated.

CONTAMINATION CHANCES

While HVAC professionals may be the reigning experts on indoor air, they are not the experts on COVID-19, Freeland noted.

“Even the CDC is trying to understand COVID-19, its transmission, the life of the virus on surfaces, how to treat, and so much more,” she said. “As stated by the CDC and WHO, there are yet many unknowns.”

Still, the HVAC industry can use current information to draw conclusions about the effectiveness of IAQ products to keep the virus out of the airstream.

John Bloemer is executive advisor and engineering fellow at Aprilaire.

“The fact that viruses can be airborne and higher MERV filters can trap them [shows that] there is some chance that in a building that has been occupied by someone who is sick with the virus, the virus could live on the filter for a short period of time,” he said. “Beyond that, we do not know enough about how the virus behaves or lives on a filter long-term.”

“As all information points to the high transmission rate of the virus and its ability to live on surfaces, there’s always a risk,” said Freeland. She said there seems to be more risk of a technician coming into contact with the virus from picking up items at a local retailer, where others might have touched the packaging before him, than from filters already installed on home air cleaners — unless someone in the home is carrying the virus.

“Media air filters capture particulates that tend to be larger than virus molecules, but depending on the filter rating (HEPA), some virus molecules and pathogens may be captured,” she said. “Since the CDC has stated that it is possible for pathogens to remain alive on surfaces for several days, that could present a risk.”

Higher filter efficiency could lead to higher contamination — simply because the filter can catch more particles.

“It seems to me that if they're trapping viruses, there's a chance there might be viruses in them,” said Tom McBride, president at Burns & McBride in New Castle, Delaware. “So the higher the efficiency, the more likely that is.”

PRECAUTIONS

While the risk is probably fairly low, there’s no reason not to take precautions, said Bloemer.

Renee Lucas, co-owner at LCS Heating & Cooling in Indianapolis, isn’t taking any chances.

“Can I say for sure that the coronavirus is being transported into the filters? I have no idea,” she said. “But some research says it can stay airborne for a few hours. We’re taking precautions.”

Those precautions include wearing protective clothing, cleaning surfaces, and disposing of filters onsite versus at the shop.

“All of our technicians wear nitrile gloves and shoe covers,” said McBride. “We disinfect the surfaces we're going to be working on, like the exterior of the heater. It's the customer’s filter, so we'll seal it in a trash bag and then they can put it in their trash can.”

Most of the technicians at LCS wear a face mask — this helps prevent breathing in particulates that may come loose during the filter change, said Freeland.

“Or we're asking the customer to pull it and we'll just take a look at it and then tell them whether it needs to be changed or not,” Lucas added. “We’re also explaining why, at this time, we don’t want to transport a bunch of dirty filters in our vans to our shop, and then we'll dispose of it wherever they want — outside, in the garbage — wearing gloves to handle it.”

Contractors should always wear PPE when changing filters, Wiser said. If the system has UVC lamps on the filters, the technician should turn off the fan and leave the UVC lamps on for 20-30 minutes before changing the media.

“Some air cleaning systems … have a permanent frame and a disposable media,” he said. “If possible, the media should be removed outside. The dirty filter or media should be sprayed with a disinfectant and carefully put into a plastic bag, sealed, and disposed of.”

If a homeowner asks for advice on how to change the filter themselves, Bloemer advised recommending a similar approach.

“Likely this is only an issue if there is someone sick in the house,” he said. “If there is, ask how long since it has been changed and if it can wait a week or two. Offer to schedule an appointment in a few weeks. If it must be changed sooner, suggest that they take the same precautions as you: wear a mask and gloves, dispose of the filter in a bag, outside the home.”

THE BEST PROTECTION

Upgrading a filter during change-out could be a good option for HVAC contractors to offer, depending on the customer’s system.

“Is that going to keep coronavirus out of your house? Not necessarily, but it's true that the better the filter, the higher the MERV rating, the smaller the particle that it'll catch,” said Lucas. “A higher MERV filter will catch smaller particles, therefore being a better option over lower MERV or fiberglass.”

McBride recently sent out an email to customers who have an Aprilaire air purifier in their home, explaining the different levels of filtration.

“We are huge believers in Aprilaire’s healthy home concept,” he said. The email explained that when they purchased their equipment, it came with “a highly efficient MERV 11 filter — but frankly, there's one that's even more efficient, and that’s a MERV 16. We attached a copy of a letter of Aprilaire has written and explained that we have them in stock. They're not inexpensive, but it has the ability to filter out smaller particles and it seems like a pretty good investment right now.”

Freeland cautioned that replacing a current MERV rating in the furnace to a higher one (such as MERV 13) can also increase the pressure drop and “adversely affect” the HVAC system performance.

“The contractor should evaluate the system to determine if a higher MERV rating can be used for the application,” she said.

If a system can’t handle high-MERV filters, due to issues like undersized ductwork, Lucas said she would recommend ductwork modifications so the customer can have the better filtration system.

“The higher, the better, and they are not restrictive from an airflow standpoint, so you provide a cleaner, healthier environment while better maintaining the HVAC system,” added Bloemer. 

CATCH, NOT KILL

While filters may catch viruses, they don’t kill them. The purpose of a filter, said Freeland, is not to “treat/remove” or “degrade/kill” COVID-19 or any other virus or pathogen. This is something customers don’t always understand until it’s explained, Lucas said.

“We have had a couple of questions like ‘Should I change my air filter more often because it’s killing viruses?’ and no — an air filter is not a cleaner. It’s not an air purifier,” she said. “People should continue to have their filters changed as usual.”

“Keep in mind that this protection will live on past the pandemic,” Bloemer added. “Cold and flu viruses happen every year.”

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