Matt Marston wasn’t sure how to react last March when a member at Basics Fitness Center in South Portland asked if he was planning to install ultraviolet lights in his building’s heating and cooling system. The light may be effective in neutralizing the virus that causes COVID-19, the member told him.

Marston knew that medical experts suspect droplet transmission as a primary cause of COVID-19. That’s when particles are flung into the air as an infected person speaks, coughs or sneezes, then fall onto surfaces if they don’t come in contact with someone nearby.

Matt Marston slides a MERV 13 air filtration filter back into the HVAC system outside of this gym Basics Fitness Center on Tuesday, July 21, 2020. Marston said they upgraded the HVAC system before reopening and purchased the MERV 13 filters. The system used to bring in about 5 percent outside air and is now bringing in about 35 percent outside air. Staff photo by Brianna Soukup

But there’s mounting evidence that even tinier particles also might remain suspended in the air and infect people – a pathway called airborne or aerosol transmission.

So Marston started looking into it. Four months later, Mechanical Services, a Portland-based heating and cooling contractor, has jacked up the center’s outdoor air flow and installed high-efficiency filters designed to trap micrometer-sized particles. Now Marston is waiting for estimates on the cost and availability of UV-C lamps, as the virus-blasting ultraviolet technology is known.

Basics Fitness has many senior citizen members, who are at higher risk for severe health consequences from COVID-19. It already requires temperature checks and hand-washing before entering the building. Confronting potential spread of the virus in indoor air is the next step.

“It’s imperative at this time that we do all we can to assure the public that we’re doing our best to make their experience safe,” Marston said.


Worries about aerosol transmission of coronavirus have Maine business owners, school administrators and heating, ventilation and air conditioning professionals scrambling this summer to upgrade the HVAC systems inside buildings. The activity level is picking up now, just as those spaces are reopening amid ongoing concerns for the health of workers, students and visitors.

Matt Marston, owner of Basics Fitness Center in South Portland, upgraded the gym’s air filtration system before reopening and the building is now circulating more outside air. “It’s imperative at this time that we do all we can to assure the public that we’re doing our best to make their experience safe,” he said. Brianna Soukup/Staff Photographer

Specific strategies vary, because every building and its HVAC system are different. In general, three measures are dominating the activity:

• Increasing the amount of fresh, outdoor air coming into a building to dilute any contaminants.
• Installing better filters that can trap viruses contained in small airborne particles.
• Killing the virus with ultraviolet light or deactivating it through an ionization process.

All those measures bring unwelcome expenses for businesses struggling to reopen and public school budgets. At the least, flooding a building with outside air increases energy use. The very idea runs counter to decades of efforts to snug up indoor space against Maine’s cold winters.

David Clay, director of product and energy services at Mechanical Services, said his firm has been contacted in recent weeks by organizations that include schools, dental practices and day care facilities.

“We get a lot of inquiries,” Clay said. “But of course, any improvements would add additional costs at a time when funds are especially tight.”



Complicating the response is the fact that aerosol transmission is an evolving and imprecise concern, so the technical specifications for how to address it are in flux.

For instance: Dental practices present a higher-risk environment for both patients and staff. The U.S. Centers for Disease Control and Prevention have issued guidance around dental offices, but no specific air quality standards. For now, the Maine Dental Association is urging its members to carry out and document air quality plans for their individual practices.

Schools also are reopening under general guidelines and are being asked by the Maine Department of Education to evaluate and maximize their existing ventilation capabilities. That includes something as simple as “outdoor air exchange using fans in open windows or doors,” according to language in the state’s framework for returning to school.

“A lot of people in a lot of different industries are waiting for guidelines,” said Rob Mitchell, president of HVAC Services in Westbrook.

But just having specific guidelines doesn’t always solve a problem, Mitchell cautioned. A good example of that is air filtration.


HVAC filter efficiency has a ranking system of 1 through 16, with higher being better. It’s called the minimum efficiency reporting value, or MERV, rating, and it measures how efficiently an air filter works. Filters with a MERV rating of 6 or lower can trap larger pollen and dust particles, while filters with a MERV 13 rating are regarded as the standard for capturing a high percentage of bacteria and virus particles.

Dr. John Dyhrberg works out at Basics Fitness Center on Tuesday. Mark Marston, the owner of the gym, said they upgraded the HVAC system before reopening and purchased MERV 13 filters. Their HVAC system used to bring in about 5 percent outside air and is now bringing in about 35 percent outside air. Brianna Soukup/Staff Photographer

The problem, Mitchell said, is that many existing heating and cooling systems can’t upgrade to MERV 13. Either the thicker filter won’t fit, or it reduces the air flow so much that the system can’t run properly.

Even simple solutions must be carried out with care, Mitchell said. Increasing the outside air supply sounds good, but in the summer, high humidity levels can create mold in air-conditioning ducts.

“Mold is going to be more problematic than the risk of COVID,” he said.

To find the right balance, HVAC professionals use specifications from the American Society of Heating, Refrigeration and Air Conditioning Engineers. In April, the trade group released a position document on aerosol transmission that went beyond the minimum standards. It noted that ventilation alone isn’t able to address all aspects of infection control and it outlined other measures, including enhanced filtration.

The society’s new document provided important direction for building professionals including Jason Donovan, facilities manager at Bangor Savings Bank.


Donovan oversees 71 buildings in Maine, New Hampshire and Massachusetts that house 1,000 employees.  Working with Mechanical Services, the bank boosted the amount of fresh air entering buildings to roughly 35 percent, low enough to increase ventilation without triggering mold. It also took fans operating on timed setbacks to save energy and switched them to always on.

Tom Colby replaces a filter in the ventilation system at the Bangor Savings Bank offices on Fore Street in Portland. The filter is the smallest micron air filter available says Colby, the facilities and purchasing coordinator for Bangor Savings Bank. Gregory Rec/Staff Photographer

“We’re just trying to push that to the maximum,” he said, “so even at night, we’re exchanging air. We pride ourselves in being as energy-efficient as possible, but this isn’t the time to do that.”

Where possible, duct work filters in the bank’s buildings were upgraded to MERV 13. Those filters will be changed more frequently, every couple of months or so, rather than a few times a year.

“These are three things I think almost everyone can do in a commercial building,” Donovan said.


Across Maine, schools are making preparations with hopes of reopening in some form in September for students and staff, bolstered by sweeping guidelines announced last week by Gov. Janet Mills.


It’s hard to generalize with schools. Heating systems in Maine range from steam-fed radiators that were popular after World War II to modern climate control systems with state-of-the art filtration. But schools haven’t been waiting for official reopening plans to evaluate their HVAC situation.

In RSU 5, which includes Freeport, Pownal and Durham, the district already had scheduled a facilities audit. But with the new COVID information, the HVAC systems became a top priority. Results of the audit are expected in the next few weeks, according to Dennis Ouellette, the facilities manager. The first step has been to make sure air supply and filtration are working to minimum ASHRAE standards, as a baseline for any improvements.

Asked if he thought the process would help reassure staff and parents who might be anxious about a return to classroom teaching, Ouellette said he hoped so.

“It’s work we have to do,” he said. “We have to make sure we’re doing all the right things.”

HVAC engineers say that perhaps the most challenging place to control aerosol transmission is in the dentist office, where rotary tools propelling bodily fluid are in constant use. While waiting for specific air quality standards for their profession, dentists are sharing information about best practices.

“It’s a hot topic of conversation,” said Dr. Brad Rand, past president of the Maine Dental Association.

Rand, for instance, has installed portable, commercial-grade HEPA air purifiers in each patient room and common areas at his Brewer office. He also had a UV-C lamp installed in the duct work.

And in another strategy to reduce aerosol transmission, some dentists are forgoing the ritual of teeth polishing during a visit. It’s only a cosmetic measure, anyway, Rand said.

“I think patients will be pleasantly surprised at the steps dentists are taking,” Rand said, noting that masks, gloves and goggles have been standard protective equipment for years. “We’ve always been at the forefront of infection control.”

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