Image Credit: Supplied

It’s summertime in America, and while there may or may not be a baseball season, some things don’t change. Hamburgers are still getting grilled, trips to national parks are being plotted and air conditioners are cranked on full blast.

That last point is taking on new meaning as the country continues its reopening in the wake of the coronavirus pandemic. Even New York City — the region hardest hit by the pandemic and the last in the country to emerge from lockdown — is on track to allow people to interact again in non-essential indoor venues starting Monday.

Barber shops, retail stores and offices will be able to reopen, with some restrictions and safeguards, and the HVAC systems that keep them cool and ventilated will come whirring back to life. Chances are you didn’t give much thought to those HVAC systems in the before-times, as long as they appeared to be working. Now, with a potentially deadly virus that spreads via airborne droplets still circulating around the country, you might be wondering, are air conditioners safe?

How the AC works

The short answer is yes, with the irritating caveat that it depends on the HVAC system and the circumstances of the space. The most tricked-out, sophisticated air-conditioner money can buy isn’t going to make much of a difference if people are packed in like sardines on a subway car or at a concert venue and an infected person starts coughing. But the presence of air conditioning likely doesn’t in and of itself increase your risk of getting the coronavirus. In fact, combined with social distancing, personal hygiene and face masks, proper ventilation and humidity control are actually great tools for guarding against infection.

A typical air-conditioner system works by taking in a certain percentage of air from the outside and mixing it with air that’s recirculated from within the building. When you’re trying to combat a virus, you want more air to come in from the outside, where it’s unaffected by whatever sneezes or coughs may be happening in a certain corner of the office. But even the recirculated air gets passed through a filter before it’s spat out from one room to the next. The gold standard is a high-efficiency particulate air (HEPA) filter and the next best thing is a filter with a minimum efficiency reporting value (MERV) of at least 13 (higher numbers are better), both of which are capable of capturing small particles such as viruses.

A study published on the US Centres for Disease Control and Prevention’s website linked the spread of the coronavirus among patrons of a Guangzhou, China, restaurant to air conditioners. But a follow-up analysis showed there was no outdoor air supply; that particular air conditioner was operating only with recirculated air, according to William Bahnfleth, a professor of architectural engineering at Pennsylvania State University and the chair of the epidemic task force for the American Society of Heating, Refrigerating and Air-Conditioning Engineers.

When it comes to both the coronavirus specifically and health and well-being overall, it’s better to have a good air-conditioning system than to not have one.


“When we see reports of super-spreading events that apparently involve air conditioning, it usually means there’s little or no ventilation in the space,” Bahnfleth said in a phone interview. Unlike other pathogens such as tuberculosis, COVID-19 doesn’t appear to be so infectious that it can spread between people in different parts of a building via air that’s been diluted through ventilation and filtration, he said.

“Infection is analogous to being poisoned,” Bahnfleth said. “You can have one drink and you’re fine, but if you drink a whole bottle of hard liquor, you may die. With pathogens, it’s similar. It takes a certain number of them to have a high probability of getting an infection. If you can reduce the concentration in the air, then the rate at which you can be exposed drops.”

The good news is that in the US, there are already minimum standards for ventilation based on square footage and expected occupancy. These usually evolve out of recommendations from the ASHRAE trade organisation and are set by local governments as part of the building code. While there are discrepancies between regions — California, for example, is one of the most progressive in terms of air-quality requirements — these basic standards are “reasonably protective,” Bahnfleth said. That’s why the most important step for any business is to do a full check-up and proper maintenance of existing systems before they start letting people back into their building, Chris Nelson, president of Carrier Global Corp.’s HVAC division, said in a phone interview.

Ensure filters are clean

Carrier, Trane Technologies Plc and other HVAC companies are offering indoor air-quality tests and restart services for buildings that have gone unoccupied for long stretches. This can help companies assess whether they’re getting proper air distribution and the appropriate influx of outside air, and to ensure filters are clean.

When it comes to evaluating what upgrades are necessary, “rather than say here’s the ‘right’ solution, we want to look at your system and equipment and see how the building operates,” Andrew Mondell, Trane’s business development manager for New York City, said in a phone interview. “Then we can think about what’s possible and how it fits into budget constraints.”

The free fix if you’re not getting enough ventilation is to just open the windows, although clearly that’s easier said than done in hot and humid places, where restaurant-goers might complain that they didn’t order a side of sweat with their fries. “As people are coming back to work and businesses are recovering, we’re cognizant of offering options people can afford right now,” Nelson of Carrier said.

One such relatively pain-free and cheap upgrade is to change your filters to a higher efficiency. Another is to adjust an HVAC system’s parameters to increase the amount of air coming in from the outside relative to the amount that’s recirculated. How easy this is depends on the particular system but for many, it’s a simple tweak with the help of a professional.

While some window AC units do allow for ventilation, they typically aren’t very effective at bringing in outside air.

- William Bahnfleth, chair of the epidemic task force for the American Society of Heating, Refrigerating and Air-Conditioning Engineers

The next level up is to look into an air scrubber with a HEPA filter. You can also add virus-killing ultra-violet light filters or other air-cleaning technology such as bipolar ionisation to your HVAC system for another layer of protection. The cost of something like that scales pretty dramatically based on the type of equipment and size of a building, from maybe a few thousand dollars for smaller, simpler jobs to many times that for a massive office building, says Trane’s Mondell. If you’re really hitting a wall on more basic ventilation and filtration fixes, you may want to replace your HVAC system with a more modern one, which is usually the most expensive route.

For consumers, this all sounds great in theory, but how do you know what businesses have made these assessments and upgrades and which haven’t? The truth is, without a technical background and a look inside the HVAC system, you don’t. But there are some things you can watch out for. Odour or mustiness can be a sign of poor ventilation.

Why bathrooms are trouble spots

While some window AC units do allow for ventilation, they typically aren’t very effective at bringing in outside air, Bahnfleth said. So if a business relies on one and isn’t doing something else to dilute the concentration of potential virus particles in the air like opening windows or limiting occupancy, that can be a worry point.

Bathrooms sometimes get shoved in wherever they fit, particularly in smaller enterprises, and often aren’t well-ventilated. A study published this week in the journal Physics of Fluids found that flushing the toilet can create a cloud of aerosol droplets that rises nearly three feet and may linger in the air or land on nearby surfaces, according to the New York Times. Keeping the exhaust fan running should help, Mondell said, and the bathroom could also be a good spot for an air-scrubber.

The net of it, though, is that when it comes to both the coronavirus specifically and health and well-being overall, it’s better to have a good air-conditioning system than to not have one.

— Bloomberg

Brooke Sutherland is a Bloomberg Opinion columnist covering deals and industrial companies.