HOW TO KEEP INSIDE SPACES WELL VENTILATED

“Deep cleaning” is the coronavirus catchphrase of the moment as more retailers, schools, and offices increase their indoor operations.

There is nothing wrong with good hygiene, and for goodness’ sake keep washing your hands, especially as COVID-19 is joined in the coming months by the flu.

But as more indoor spaces prepare to reopen this fall, infectious-disease experts say we don’t need to be quite so fanatical about cleaning surfaces — at least not to the extent that it distracts from the main route of transmitting the coronavirus: through the air.

That means continuing to stick with methods that work. Wear masks. Practice social distancing — an effective safeguard against larger virus-laden droplets that fall to the ground within a few feet.

And when going indoors — given that smaller viral particles can remain aloft — consider the ventilation.

Despite evidence the virus can live on surfaces for days, there are few, if any, confirmed reports of people getting COVID-19 from touching a germy object, said Amesh Adalja, a senior scholar at the Johns Hopkins Center for Health Security. That doesn’t mean surface transmission of COVID-19 can’t happen. It almost certainly does, given our knowledge of other viruses, said Gregory A. Poland, a vaccine researcher at the Mayo Clinic. Nevertheless, the primary route through which the coronavirus spreads is the air.

That leaves two primary options for when indoors, said Michael S. Waring, a Drexel University professor of civil, architectural and environmental engineering. Bring in fresh air, filter the air already in the room, or both.

Here are the basics for keeping spaces well ventilated:

1. Get to know HVAC and MERV

A high-quality HVAC (heating, ventilation and air conditioning) system will refresh the air in a space multiple times an hour, though the ideal rate depends on the size of the room and how many people are in it. Commercial HVAC units generally are equipped with filters, rated with a system called MERV: minimum efficiency reporting value. Look for one with a rating of MERV-13, Waring said. That means it is designed to remove 90% of particles that measure one micron — a millionth of a meter — or more. And just as important as the filter’s efficiency is how well it fits, Waring said. Gaps and leaks defeat the purpose.

2. Use a standalone filter

In buildings without HVAC units, another option for removing viruses from the air is a standalone air-cleaning device equipped with a HEPA filter, Waring said. Some air-handling systems tout the use of ultraviolet light, which is known to kill viruses. But be aware of its limitations, said Joshua Santarpia, an associate professor of pathology and microbiology at the University of Nebraska Medical Center. Do not expect it to help much in air that is moving through ductwork. UV light takes tens of seconds to inactivate a virus, and the air in an HVAC system is moving faster than that. “You don’t really get enough time,” he said.

3. Open the windows

In older buildings without HVAC units, opening windows is a common-sense alternative. Crossventilation works best: opening windows on opposite sides of the room. For improved flow, place an outward-facing box fan in one window and an inward-facing fan in the other.