GIMME SHELTER- Fresh air fan? Open a window, keep it moving
Q: What can be done to improve the air quality and air circulation in our house? Will fans do the trick, or should we be thinking about other systems?
A: It might first be useful to consider "ideal" homes in regard to air quality and circulation: One is a well-built mainstream modern house. It has a high-efficiency air-to-air heat pump that provides ducted heating and cooling to all the rooms, with efficient returns to help circulate the air. If it's done well, this house doesn't need fans, or even shade.
Another example is a well-built 150-year-old house with very poor insulation (by our standards), no duct work, no fans, and coal or wood heat. The builder would have offset these facts by optimizing the orientation to use the sun for winter heat and added eaves and porches for summer cooling. This is probably the healthiest of homes to live in. It's a little hotter in the summer, and definitely colder in the winter, than our modern tastes are used to, but it offers lots of fresh air and natural circulation. The utility bill is virtually nonexistent.
Any house, with the exception of our first example, benefits from good attic and crawl space ventilation. Opening and closing windows on the upstairs/downstairs at the proper time of day is a lost art (follow your intuition!). Shutters were once used– curtains and blinds can perform the same function, albeit on the wrong side of the glass. Sometimes it's better to close downstairs windows in the heat of the day (this is where shutters were excellent– they blocked light and heat but allowed some air flow), while doing anything at your disposal to get heat out of the upstairs and attic. The entire house would then be opened up in the evening.
Poor air quality is hard on human lungs– we evolved breathing good air.
"Fresh air" is air that has been naturally exposed to sunlight, rain, aspiration by plants and animals, and which is circulated, mixed, and renewed via wind and natural convection. Stale air is air that through entrapment, or lack of circulation, fails to be part of this cycle. The best way to improve stale air is to release it so it can be freshened and replaced by fresh air. Fans circulate air, but if your house is all closed up and poorly ventilated, you can end up circulating stale air. This is better than un-circulated stale air, but you need to bring in fresh air too. Open a window.
Air flow relative to humidity is really tough in the South. If you have a problem home, and are not looking at the more expensive remodeling solutions, then a combination of fans, dehumidifiers, and window AC units (in my personal order of preference) are what's available. Keep in mind that, in a house without AC, moist, hot air that's circulating is a big improvement over moist, hot air stagnating in place.
In my opinion, the best new house of all would draw heavily on traditional wisdom but would augment it with 21st century foam insulation, passive solar, and ventilation techniques. This house is cheap to air-condition and even in an extended power outage, comfortable 365 days a year. That's what we should be building.