· by Michael Blair, Nashville's Air Duct Cleaning
Indoor air quality has three levers — filtration, humidity and ventilation — and they address different things. In Middle Tennessee the humidity lever is the one most often ignored and frequently the most effective.
Filtration
A better filter helps, up to the point where it restricts airflow. Higher-rated filters need more surface area, which is why a four- or five-inch media cabinet outperforms a high-rating one-inch filter.
The most common filtration failure is not the rating but the seal — air bypassing a filter that does not fit its track properly.
Humidity
Between 45 and 55 percent is comfortable and suppresses dust mites and mold. Most Nashville houses run well above that in summer without dehumidification.
A whole-house dehumidifier addresses the shoulder seasons when it is humid but not hot enough for the air conditioning to run enough.
- A four or five inch media filter over a high-rated one-inch
- Check the filter actually seals in its track
- Target 45 to 55 percent relative humidity
- Seal and dehumidify the crawl space
- Vent bathrooms and the kitchen outside, not into the attic
The crawl space again
Air moves upward through a building, so crawl space air becomes house air. In Middle Tennessee a vented damp crawl is often the single largest contributor to poor indoor air.
Encapsulation frequently does more for indoor air quality than any filtration upgrade.
Ventilation
Modern tighter houses need deliberate fresh air, and older leaky ones get it whether they want it or not. Bathroom and kitchen extraction must terminate outside.
A bathroom fan discharging into the attic is common here and moves moisture from one part of the house to a worse one.