The vast majority of SARS-CoV-2 transmission takes place indoors, usually by inhaling airborne particles that contain the coronavirus. But despite the obvious risks within, according to the Centers for Disease Control and Prevention, small household gatherings drive many of the recent increase in the number of cases.
The best way to prevent the virus from spreading in a home is to keep infected people away. But this is difficult to do as an estimate 40% of cases are asymptomatic and asymptomatic people can is still spreading the coronavirus to others. The next safest is for entertaining outdoors, but if you can’t, there are a few things you can do to reduce the risk of the coronavirus spreading.
First – and most important – always wear masks, keep everyone at least 6 feet away from other people and don’t spend too much time indoors. But in addition to these precautions, making sure the air inside is as clean as possible can also help. I’m a researcher indoor air quality who studies how the transmission of infectious diseases by air. Using increased ventilation or running one air filter or filter of the correct size can add an extra layer of protection.
Fresh air is safer air
A safer home is one that constantly has a lot of outside air replacing the stale air inside.
Houses are usually ventilated through open windows or doors, or air that leaks in through unintended openings and cracks in the building itself. A typical air exchange rate for a home is round 0.5 air changes per hour. Because of the complicated way air moves, this means it takes about two hours to replace two-thirds of the air in an average home and about six hours to replace everything.
This slow air exchange is not good if you want to limit the spread of an airborne virus. The higher the ventilation speed, the better – how much fresh air is ideal? While the exact exchange rate depends on the size of a room, a 10-by-10-foot room with three to four people should be at least three air changes per hour. In a pandemic, this should be higher, and the World Health Organization recently recommended six air changes per hour.
There is no need to know the exact air exchange rate for your home; just know that more is better. Fortunately, increasing the ventilation of a house or apartment is easy.
Open as many windows as you can – it bigger the opening all the better. Open doors to the outside. Run the exhaust fans in your bathroom and above the stove – but only do this if the exhausts go out and if you also have a window or door open. Plus, you can place fans in open windows and blow the indoor air out to boost your airflow even further.
I live in Colorado and the winter cold has arrived. I still think it’s worth it to have windows open, but I don’t open them until halfway and turn on the heaters in my house. This wastes energy, but I keep the time I have for this to a minimum, and once visitors leave, I keep the windows open for at least an hour to fully air the house.
All these things add up and increase ventilation.
Filtration as a backup
If you are concerned that the ventilation in your home is still too low, air filtration can provide another layer of security. Just as an N95 mask works, air in your home can trap streams of airborne particles through a filter with small openings that may contain the coronavirus.
There are two ways to filter air in the house: with a built-in system – such as central heating – or with stand-alone air purifiers.
In my house, we use both air purifiers and our heating system to filter the air. If you have central heating make sure you have furnace filter has a minimum efficiency reporting value (MERV) of at least 11. This value describes how effective a filter is in removing airborne particles and contaminants from the recirculated air. The standard on most furnaces is a MERV 8 filter, and many furnaces cannot operate with a more efficient filter, so be sure to check your filter and ask a technician before replacing it. But a MERV 8 filter is better than no filtration at all.
You can also use a stand-alone air purifier to remove particulate matter, but how effective they are depends on the size of the room. The bigger the room, the more air that needs to be cleaned, and standalone cleaners are only so powerful. My house has an open floor plan so I can’t use my air purifier in the main living space, but it can be useful in bedrooms or other smaller enclosed areas. If you are considering purchasing an air purifier, I have created a tool you can work with together with some colleagues from Harvard determine how powerful an air purifier you need for different room sizes.
And don’t forget to consider how effective an air purifier’s filter is. The best option is a cleaner that has a high-efficiency particulate air (HEPA) filteras these remove more than 99.97% of all particle sizes.
If you decide to share your home with others in the coming months, remember that being outside is by far the safest. But if you do need to be indoors, reduce the length of your guests’ stay, wear masks and always keep a social distance. In addition to these precautions, keeping airflow through opening windows as far as possible, blowing more air into your home with exhaust fans, and using air purifiers and filters can further reduce the chances of spreading the coronavirus.