(NEXSTAR) – When smoke from wildfires turns the outside air unhealthy, is it safe to run the air conditioner?

An oppressive blanket of smoke from over 100 Canadian wildfires rolled over the East Coast and Midwest Wednesday, leaving many residents concerned about the air quality.

Dr. Brian Christman, a professor of medicine at Vanderbilt University told Nexstar’s WJW that running the air conditioning is fine, so long as the right settings are used.

Most air conditioners operate by cooling the air inside the house and recirculating it, not pulling in air from outside. Some units, however, are equipped with a fresh air function, which should not be used.

“I wouldn’t spend a lot of time outside,” Christman said. “I would try to set your air conditioning on recirculate so that you’re not breathing in as much of the outdoor air and if you have good level filters on your air conditioner, make sure that they’re in place and that you’re using them.” 

The Environmental Protection Agency has the following tips for keeping your inside air as clean as possible:

• Find out if you have a fresh air intake mode and make sure it is set to “recirculate” instead. Be sure the filter is in good shape and consider upgrading to a MERV 13 or higher rated filter if your HVAC system can accommodate it.
• If you have an evaporative cooler, try not to use it in smoky conditions because it can draw more smoke in. Fans and window AC units are better options.
• If you’re using a window unit, make sure the seal between it and the window is as tight as possible and figure out how to close the outdoor air damper. If you can’t close the damper for some reason, consider using a fan in the home intstead.
• If you have a portable air conditioner with a single hose that’s set up to vent out of a window, do not use it because it can allow more smoke to come inside. Think about using a window AC unit or fan instead.

Air quality reaches hazardous levels

By Wednesday, air quality reached unhealthy levels across broad swathes of the U.S., stretching south from Canada as far as North Carolina, with air quality reaching hazardous levels in New York City and parts of Pennsylvania.

Dr. Robert Dracker, medical director for Summerwood Pediatrics in Liverpool, New York is reminding everyone that any exposure to smoke is not good for you.

“You don’t need to inhale smoke if you don’t need to,” said Dr. Dracker. “I mean, when I was a kid, my father smoked in the car and I was always inhaling smoke, probably greater than what the warning is now if you think about it, but we’re very concerned with air quality, and usually in Central New York we have good air quality but when it’s obvious, just like the yellow coloration of the sky right now, it’s silly to really do that.”

The contaminated air had also stretched west to Ohio by Wednesday, where Dr. Loren Wold, associate dean of research operations and compliance at the Ohio State University College of Medicine told WJW, “People, if they were to be outside, especially if they’re exercising, breathing faster, they’re going to be inhaling particulates at concentrations that normal smokers would inhale.”

With some rain in the forecast for the Northeast and Mid-Atlantic this weekend or into next week, residents may get some reprieve from the noxious smoke, U.S. National Weather Service told the Associated Press. Real relief, however, will only come once the massive blazes are extinguished, they added.