I’m sure you know that if you say “Beetlejuice” three times, he appears. Well, if I write
about something three times, I mean it. Yes! By all means, when the weather is nice, open windows. Install a screen door and allow that great outside air to flow in. Of course, when the weather is too cold or too hot or too blustery or too wet, we close everything up. Makes sense. But when do we get more colds? Generally, we get them during the winter when our house is all closed up.
When I was a kid, I never heard of a “summer cold.” We were out in the sun and fresh air most of the time and inside we had to open windows and put in a fan to bring some often not-so-cool air in from outside. Now we have air conditioning and people routinely get summer colds. The key to all of this is “air change.” But I’ll tell you another secret advantage of bringing outside air in via your heating and air conditioning (HVAC) system.
Most residential HVAC systems re-circulate the air. In other words, it is for the most part a closed system. When doors and windows are closed, the only air that comes in from outside is when someone enters or exits through a door to the outside. And guess what. Under those conditions there is little to no air change. That means that any contaminants that are normally present in the house and especially those generated in the house will build up. This includes:
1) Volatile organic compounds (VOC) and formaldehyde that are included in such things as carpeting, paint, solvents, cleaning supplies, furniture, etc. Proof of this is simple. Keep a room closed up for a week or two. No window, no door open to outside or even to the rest of the house. No matter what you have in the room, there will be an unpleasant odor. You need to be getting air change in that room. That happens to a lesser degree in a house that is closed up. People come and go so there is some air from outside, but this is minimal so these VOCs build up, increasing exposure to occupants.
2) People are producers of contaminants. The most obvious problem with people in a closed system is when one person brings home a cold or flu or some other illness. Without significant air change by bringing in outside air, all people in the house are exposed to greater numbers of the microbes that are the source of the illness. So you have the phenomenon of passing a cold or other illness from one person to another in the house. You see the same situation in an office or a school room with insufficient outside air. One person gets sick and it makes the rounds of the office or classroom.
3) You can’t mention air quality problems without talking about the “M” word – mold. If you do have a mold growth location in the house, referred to professionally as a “mold amplification” point, it is more of a problem with insufficient outside air or low air change. You have a greater concentration of mold spores in the air and therefore greater exposure due to the lack of sufficient air change. Often amplification points are not noticed. If the source of mold growth is water intrusion into wall cavities, mold growth goes unnoticed. But out of sight does not equate to unable to cause exposure. Walls are not sealed. Air can move through walls as pressure changes in the house such as by doors opening and closing or due to varying wind speed or direction.
4) Radon is a radioactive gas that is colorless, odorless and tasteless. It results from decay of uranium or thorium. This decay takes place underground as a normal process. Where this process is occurring, the gas seeps to the surface and can enter buildings through crawl spaces or cracks in slabs. Radon “Progeny,” formerly known as Radon “Daughters,” (I think maybe political correctness might have had a hand in the name change) are solid particles that are produced by decay of radon gas. They tend to attach to dust particles in the air, which are hazardous when breathed into the lungs. Lung cancer can result after years of exposure. As with other contaminants, Radon Progeny will become more concentrated due to a lack of air change. Another factor validating having outside air provided via the HVAC system is pressurization. Outside air brought in through the ventilation system positively pressurizes the building or house. This means that filtered air from outside has to find its way out in order to equalize the pressure. So where you might have air flowing in under a door or through some other crack or break in the building envelope, you now have air flowing out through these areas. This helps to prevent air infiltration, including from crawl spaces or through cracks in slabs. Thus exposure to radon contamination is reduced or eliminated.
Certainly, good filtration and ensuring that your HVAC system remains relatively contaminant free by periodic cleaning is a necessary condition for reduced exposure. I generally recommend that coils be cleaned annually, as the major potential source for mold growth. The entire HVAC system should be cleaned every five to eight years based on their environment and how much they are used.
I’m sure there are other potential contaminants that have not been covered in this article, but surely this is sufficient to illustrate the importance of air change with air from outdoors. It has been my experience in virtually thousands of indoor air quality investigations that insufficient outside air has been a factor in most of them. Thus I say, “Air Change, Air Change, Air Change.”