HVAC and Wildfire Smoke Pollution: Expert Interview

“Climate change is a real thing. The forests are drier than they used to be. They burn more easily, with less provocation, and they’re harder to put out…We used to have a fire season, but there isn’t a specific season anymore.”

Michael Gallagher, PE, ASHRAE Guideline 44 Committee Member

In July 2026, rapidly expanding wildfires in Ontario sent dense plumes of smoke across the American Midwest, Mid-Atlantic, and Northeast. Social media lit up with apocalyptic orange skies. Air quality alerts were issued across more than 20 states, pushing some communities into what the EPA defined as a “very unhealthy” or “hazardous” range.

The principal health threat in wildfire smoke is fine particulate matter. It’s what makes a smoky sky look hazy. Fine particulate matter can travel hundreds or thousands of miles, sneaking into buildings and penetrating deep into a person’s lungs or even the bloodstream. Numerous scientific studies have linked particle pollution exposure to a variety of serious health problems (EPA 2026).

The human body isn’t well equipped to filter out the particulate matter in wildfire smoke. But homes and buildings, with the right HVAC equipment and the right preparation, can make a difference.

Building a Smoke Readiness Plan

“If you can see smoke outside, then there’s a good chance some of that smoke can get inside, too,” says Michael Gallagher, PE. “If you don’t take any action at all, you’ll end up breathing it in.”

Gallagher is a committee member of ASHRAE’s Guideline 44: Protecting Building Occupants from Smoke During Wildfire and Prescribed Burn Events. Applying to both commercial and institutional buildings, it outlines best practices for building design, operation, and maintenance to reduce the health risks associated with prolonged exposure. The guideline also requires a smoke readiness plan (SRP), particularly for wildfire smoke.

“It’s about preparation,” Gallagher says. “If you wait until the smoke is upon you, your options are pretty limited.”

A smoke readiness plan is devised by the person or persons who operate and manage a building. The first step is ensuring a building has access to the necessary materials to help it cope. Buildings go through air filters much more quickly in a smoky environment; if you wait until smoke’s in the sky, there won’t be many air filters left on the shelves. The same is true for personal protective equipment (PPE), like masks.

An SRP also requires an assessment of the building itself. Over the last ten years, for example, many buildings have gotten surveillance cameras installed—but not every installation has made sure to seal up the conduits that penetrated the building. If they didn’t, the building envelope’s compromised.

“In some cases, it makes sense to use the air conditioning system to help pressurize the building and keep smoke out,” Gallagher says. “But if your building is old, the building envelope is probably like Swiss cheese.”

A building’s specific SRP will depend on its parameters of operation. Will it continue to be occupied during a smoke event? At what capacity? The building envelope can be sealed up, but to get positive air pressure will require bringing in some level of air from the outside. If that air’s smoky, it requires an appropriate filter situation.

“The tighter your building is, the easier it is to pressurize, and the less outside air you have to bring in,” Gallagher says. “That means less air you have to filter, which means filters last longer in a fire event. The guideline goes through things like this to consider, but not all buildings are the same. You may have some unique requirements.”

The Role of HVAC in Combating Wildfire Smoke

Especially in commercial buildings, a large amount of outside air is typically brought in for ventilation purposes. Building codes require a certain amount of what used to be called fresh air to be brought in. But during a smoke event, the air isn’t fresh (building codes now call it outside air). Building operators need to know exactly how much outside air is being brought in.

“During Covid, the solution was dilution,” Gallagher says. “Pretty much everyone increased the amount of outside air being brought in, to dilute what was inside. A lot of buildings never reversed that strategy.”

Building management changes often, especially in the commercial space. So the group that was in charge during Covid might not be there anymore, and the people who are there won’t know just how much outside air is being brought in, and where. An SRP needs to take this into account.

For larger, more recent buildings—those built in the last 10 to 20 years—digital control systems might give enough flexibility to be able to switch airflow between the conditions appropriate for an airborne pandemic and those appropriate for a wildfire smoke event. But there’s a very good chance that they’ve never been set up to do that.

“Human beings don’t do anything until they’re given a reason to do so,” Gallagher says. “But climate change is a real thing. The forests are drier than they used to be. They burn more easily, with less provocation, and they’re harder to put out. People are finally becoming aware of this. We used to have a fire season, but there isn’t a specific season anymore.”

Typically, ASHRAE committees are entirely made up of engineers. But for Guideline 44, about half of the committee were engineers and half were health scientists. It also had many Canadians: Canada has dealt with wildfires for a long time, and their government has put a lot of effort into figuring out how to cope.

“The first step has to be awareness,” Gallagher says. “We’re on the way towards that. A decade ago, on a scale of one to ten, awareness of this issue was probably at one. Today, it’s at seven or eight, at least in the design community.”

The Role of HVAC Technicians

For HVAC technicians counseling their clients, it’s not all doom and gloom. Despite the pivot towards a larger intake of outside air, Covid taught the community a lot about filtering fine particulate matter. That’s especially relevant during a wildfire event. The tech’s here. It just needs to be implemented.

“During a wildfire event, you probably want to upgrade your air filter,” Gallagher says. “The gold standard for residential right now is the MERV 13.”

A MERV 13 will catch a lot of small particulate, around 75 to 80 percent. Stepping down to MERV 11 catches only about half. But going up past MERV 13 starts to become counterproductive: the more efficient a filter, the dirtier it gets, and the more resistance to airflow it creates. Residential systems aren’t equipped to handle that.

“An HVAC technician should counsel their client that if they use a MERV 13, they have to pay attention, because it will do its job,” Gallagher says. “It’ll catch particulate matter. That means it’ll get dirty and need to be changed sooner. There are all kinds of problems that go with not changing a filter when it gets clogged.”

Homeowners and building managers might want to store extra air filters on-site. Like masks, they won’t be on shelves when they’re needed most, and it can take suppliers a while to restock. They might want to buy extra and store them—like masks, they won’t be on the shelves when they’re needed most. For a larger commercial building, with outside air being filtered in to keep things pressurized, it’s possible that filters would need to be changed multiple times a week.

“In a residential situation, traditional air conditioning can help you clean the air, but especially if the home isn’t well-sealed, I’d recommend in-room air cleaners,” Gallagher says. “You can either buy them or build them yourself. But it’s another thing you want to think about in advance. If you wait until you absolutely need it, the opportunity may have passed.”

HVAC technicians can help residential homeowners inspect their building envelope. In addition to reducing the amount of wildfire smoke that enters a home, tightening the building envelope can help with issues like energy efficiency and pest control. Small improvements can make a big difference.

“For an HVAC technician viewing a home for the first time, there are things that are obvious to them that the homeowner can’t see,” Gallagher says. “I don’t know about you, but if you put something in the corner of my living room, after it’s been there more than two weeks, it may as well be invisible to me. I think that’s generally true for homeowners across the board.”

The Future of HVAC and Wildfire Smoke

Work on Guideline 44 started in 2020. The guideline was published in November of 2024. Since then, progress toward implementation in the field has been made, but it hasn’t been as fast as the adaptation to Covid, which was more immediate and widespread.

“It affects a smaller segment of the population, but from a health standpoint, wildfire smoke can be a life-and-death situation,” Gallagher says. “The committee that generated Guideline 44 has been put on permanent status. There’s been some really exciting research. We’re in permanent update mode.”

Much of the research is coming out of Canada, and it points to wildfire smoke’s dynamic nature. Over time, smoke’s composition changes. Some of the heavier particulate falls out, while the really fine particulate becomes more obnoxious. That means that the best strategy during the fire event itself might not be the same as the best strategy weeks later, with wildfire smoke still hanging in the air. But while research and guidelines move at one pace, implementation is likely to be slower.

“It only took a few months, during Covid, to incorporate some pretty reasonable strategies into the design mentality,” Gallagher says. “Wildfire smoke is a slower process. There isn’t a gun to everyone’s head. But it’s visible, at least. In five years, I suspect a lot of this will be much better understood and much more commonly practiced.”

Matt Zbrog

Matt Zbrog is a writer and researcher from Southern California. He's been living abroad since 2016. Long spells in Eastern Europe, Southeast Asia, and Latin America have made the global mindset a core tenet of his perspective. From conceptual art in Los Angeles, to NGO work on the front lines of Eastern Ukraine, to counterculture protests in the Southern Caucasus, Matt's writing subjects are all over the map, and so is he.

HVAC and Wildfire Smoke Pollution: Expert Interview

Building a Smoke Readiness Plan

The Role of HVAC in Combating Wildfire Smoke

The Role of HVAC Technicians

The Future of HVAC and Wildfire Smoke

Matt Zbrog

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