Now that June has arrived, we are finally leaving the windows open and breathing in the best air of the year. Even if you live in a harmless little town of 24,000 like Kingston, the air inside your home is almost never as good as the air outside.

According to the government, we spend 90% of our lives indoors. How dangerous this is depends on factors such as the heating system we use, how airtight the house is, whether we smoke, and whether we continue to release substances such as formaldehyde. The best heating systems in terms of maintaining indoor air quality do not use the oxygen inside the house to burn and then vent all the pollutants outside.

A portable kerosene heater fails on both counts and causes a steady deterioration in air quality. At the top end of the scale are central heating systems that do it right. The best? Heat pumps that are absolutely excellent.

Another important cause of indoor air pollution is the release of harmful chemicals, especially formaldehyde, from household items and new buildings. Among the worst offenders are chipboard and chipboard used in shelving, speaker systems, and other pressed wood products, as well as some synthetic carpets. Chipboard can emit ten times more formaldehyde than outdoor plywood. When used as a subfloor, pressed board gases emanate from the finished floor for months and even years.

Another source of indoor air pollution is mold, spores and bacteria caused by standing water or occasional wetness. A damp basement will breed them, and all carpets and rugs that come in direct contact with concrete will almost automatically retain moisture, which in turn usually causes biological problems. Air conditioners are good machines for dealing with dampness and may be the culprit as they cover puddles of water. These are ideal breeding grounds for microscopic pathogens. Any time you smell mold near an air conditioner or humidifier, you should automatically open the device (after unplugging it), clean it with disinfectant, and let it dry.

All indoor air pollution problems are mitigated—or exacerbated—by the amount of ventilation in the home. Now in the summer we have nothing to worry about at all. And during the rest of the year, a typical house has a complete change of air every hour, simply because houses leak, especially around windows and doors.

But in a “pressurized” low-energy home, like many pre-30-year-old frame houses, air changes can take four to five hours to complete and serious amounts of pollutants can build up.

Since this is the “Night Sky”, you may be interested to know that outdoor air quality at night is almost always much better than during the day, and this effect is much more noticeable in big cities. Particulate matter from diesel trucks, buses and factories naturally build up during working hours and when commuters are most active. In addition, tiny droplets of water in the air, evidenced by the milky color of the sky and the intensity of which depends on humidity, carry pollutants directly to your lungs, and at night this air is both drier and cleaner. You can see why this is better than what’s circulating in your home, as there are 60,000 chemicals currently in widespread use, according to the EPA, especially in building materials such as paint, polyurethane, cleaners, and adhesives.

So, try to remember to do often what you are already doing this month. Open the window.