December 22, 2020

Easy ways to improve your air quality when dining moves indoors


Scientists are still learning about COVID-19, but one thing they agree on is that it’s primarily transmitted through the air from one person to another. The coronavirus hitches a ride on droplets or even smaller aerosolized particles, making people’s best defenses physical distance, physical barriers such as masks or shields, and good airflow or ventilation.

“What science is learning about the coronavirus is that when aerosolized it can hang in the air like smoke,” says Danny Miller, president of Transformative Wave, Kent, Wash. “Those who remember when smoking was allowed in restaurants know that smoke can linger for hours.”

You’ve already likely taken steps to accomplish the first two goals such as operating at 50% occupancy or less, moving tables apart, putting up plastic barricades and asking staff—and guests when they’re not eating—to wear masks. 

There also are many simple things you can do to optimize your HVAC and CKV systems to improve ventilation and airflow, both in your dining area and kitchen.

Clearing the air

If patrons are safe outdoors if they’re physically distancing, how much fresh air should you bring indoors when they dine in? Experts say that 10 liters/second per person is a good target during a pandemic. 

In a 10x10-ft. room with four people, that would translate to an air exchange rate of six times an hour. 

A 2016 study in a Hong Kong hospital showed that an exchange rate of nine times per hour was substantially more effective than six at reducing the spread of other coronaviruses such as SARS, MERS and H1N1. 

Calculating how much air your HVAC moves and how much fresh air you need to bring into your restaurant isn’t easy. But Shelly Miller, professor of mechanical engineering, University of Colorado, Boulder, Colo., who specializes in controlling infectious airborne diseases indoors, says there’s an easy hack for peace of mind.

CO2 levels can indicate how much ventilation a space gets. Outdoors, CO2 levels are just above 400 parts per million (ppm). In a well-ventilated room, they’re double that—about 800 ppm. 

Since we exhale CO2 (along with coronavirus if we’re infected), rates higher than that indicate the room needs more ventilation. You can get a good CO2 meter for about $100 online, according to Prof. Miller, but be sure to calibrate it properly.

“We monitor a wide range of operations with CO2 sensors in place,” says Transformative Wave’s Miller, “and we generally find that restaurant operators really don’t need to worry about it much compared to other retail spaces because of how much air moves through restaurants due to both HVAC and kitchen exhaust demands.” 

Front-of-house strategies

To optimize your HVAC system, the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) and experts like Transformative Wave’s Miller and the Food Service Technology Center (FSTC), San Ramon, Calif., recommend the following:

  • Make sure your rooftop HVAC unit is in good working condition. 
  • Make sure your economizer is in good working condition. Check that the dampers work and open them if outside air conditions are suitable.
  • Clean or replace filters to keep static pressure down, increase airflow and save money.
  • Upgrade to MERV-13 filters or better if your HVAC system can handle the increase in static pressure and still provide adequate exchange rates.
  • Maintain an indoor relative humidity of between 40%-60%. The coronavirus seems to fare best in more humid or drier conditions. For whatever reason, it doesn’t survive as well in the 40%-60% humidity range. 
  • Make sure inside vents and diffusers have been cleaned and sanitized.
  • Check that restroom fans are working and clean.
  • Keep your HVAC system on overnight or for at least two hours before opening and after closing.

UV-C light also kills pathogens like the coronavirus, and several companies now make room air purifiers that use both HEPA filters and UV-C light to help clean the air.

Back-of-house basics

In the busy close quarters of the kitchen, good airflow is even more important. To provide adequate ventilation:

  • Let your demand-control kitchen ventilation (DCKV) system (if you have one) maintain the proper airflow for best hood capture and containment. However, use manual override to increase airflow when needed, such as during a rush or when you’re receiving a delivery.
  • Run the exhaust hood fans overnight or for at least two hours before opening and after closing to replace the air in the kitchen. 
  • Improve your exhaust hood’s capture and containment by pushing appliances against the wall, making sure there’s a 6-in. hood overhang over the front and sides of equipment, adding side panels to the hood, and eliminating four-way diffusers near the hood by using perforated diffuser or fabric vent socks. (Four-way diffusers disrupt the flow of exhaust from the cooking area up to the hood.)

For more information on ventilation during the pandemic, see these resources: