4 ways to know if you're in a well-ventilated space, reducing the risk of spreading or contracting the coronavirus

• A growing body of research shows the virus spreads in crowded, poorly-ventilated rooms.
• Experts told Business Insider the best way to know if a room is poorly-ventilated is to trust your sense of smell and check for open windows.
• It's a good idea to ask your landlord or handyman what kind of air is being supplied to your home.

As businesses, stores, cafes, and restaurants gradually reopen across the US, experts are gently urging people to pay attention to ventilation.

Research has shown that the novel coronavirus primarily spreads in indoor spaces without proper circulation. To prevent more serious upticks in cases of COVID-19, the disease caused by the coronavirus, it's essential that any indoor spaces where people are congregating are ventilated with a fresh airflow.

In late June, New York governor Andrew Cuomo announced that all of the state's malls looking to reopen will need high efficiency particle air filters, or HEPA filters, that can filter out the coronavirus, instead of "just recirculating the air with the virus." He recommended that offices and other businesses look into similar options.

This is a debate that is playing out in homes, offices, bars, and restaurants all across the country, as businesses are keen to get back to work, without becoming a hotbed of infection, as was the case in one Michigan bar where 100 people contracted the coronavirus.

Business Insider spoke to experts in engineering who offered a few key ways to know that a room is properly ventilated, and what to do if it isn't.

If there's natural ventilation, you'll be able to spot it easily

"There are two types of ventilation: mechanical ventilation and natural ventilation," L. James Lo, assistant professor of civil, architectural and environmental engineering at Drexel University, told Business Insider.

Natural ventilation is easy to spot, he said, because there will always be a visible connection to the outside, whether that's an opened window, door, or atrium. Mechanical ventilation, on the other hand, uses fans to move outdoor air inside and it is difficult to see.

"If a person is placed in a well-ventilated space versus a not-well-ventilated space, the difference should be very distinct by personal feels," Lo said. "A poorly-ventilated space will have accumulated indoor pollutants and occupants can feel discomfort, drowsiness, and dizziness if sensitive to those pollutants."

Trust your nose

Qingyan Chen, a mechanical engineering professor at Purdue University, says relying on your sense of smell can be key. "Our noses are actually very good sensors of building ventilation," he told Business Insider.

Smelling stuffy room air is a sign that carbon dioxide concentration is high, and the ventilation is poor, he said. Smelling volatile organic compounds, or strange smells, is another sign the ventilation is bad.

On the flip side, feeling strong air movement indoors is a sign of high ventilation, and opening windows is a quick, easy way to bring more outside air indoors.

Older buildings are less likely to have proper ventilation

Newer buildings often have proper ventilation that older buildings do not, Lo pointed out. The older buildings, which may have been remodeled or repurposed, may not have had the HVAC system replaced with a newer one because of budget constraints.

Before the invention of AC systems, windows were the original ventilator system, and many old buildings and some single family homes still rely on windows for air circulation.

And if the space you're in was repurposed for a different occupancy and use, like a former gym turning into a condo, the previous HVAC system, designed for a different scenario, might not be able to provide adequate ventilation.

If you're in a building that is not receiving any outside air, ask to open a window

"Open windows can bring a lot more outside air indoors than mechanical ventilation can, which I would strongly recommend," said Chen. Both Chen, Lo and Bahnfleth all pointed out that opening a window was optimal in situations where there was no outside air being filtered in.

Recently Dr. Anthony Fauci, the US's top infectious-disease expert, noted that case numbers could go up if people didn't exercise caution. "I would not be surprised if we go up to 100,000 a day if this does not turn around," he said. "I am very concerned."