5/5/2014

Ventilation IAQ

Spring has sprung and pollen is in the air! It’s during this time of year that we focus on allergies and asthma and the air in our homes. We start to open the windows to let the fresh air in, and we start to sneeze.

With the increased focus on IAQ, ventilation becomes an important subject. We’d like to discuss the different methods of providing fresh air to our homes, and how these different methods can have different results.  There are three methods of providing ventilation:

  1. Exhaust-Only Ventilation
  2. Supply-Only Ventilation
  3. Balanced, Whole-House Ventilation

Exhaust-Only Ventilation is usually accomplished with bath fans and can be continuously running fan(s) or intermittent running fans, usually when taking showers or baths and producing lots of steam and moisture. Thee are some pitfalls with Exhaust-Only Ventilation. It can result in a negatively pressurized home, which means that replacement air is pulled in to the house through cracks and openings. This often occurs through crawl spaces, basements, and sills, or from attics through openings such as light cans. And this can result in mold, VOCs, dust mites, fine dust, and radon being drawn into the house.

Supply-Only Ventilation is usually accomplished by connecting a duct from outside to the return plenum of an air handler at the furnace or air conditioner. This pressurizes the house, pushing warm air out through the cracks in winter, and pushing cool, air-conditioned air out through the cracks in summer. It also requires that the air handler is running continuously to distribute fresh air, even when you are not heating or cooling the home.  You also still need bath fans that are running opposed to the incoming air while operating.

Balanced, Whole-House Ventilation provides controlled fresh air to those spaces you want fresh air and removes stale, humid air from those spaces that you want to exhaust, such as bathrooms, kitchen, and laundry. It does this while capturing heat (in winter) from the outgoing air and transferring that heat to the incoming air, saving energy.  The incoming air can be filtered to eliminate pollens and other allergens. These filters can be at levels up to HEPA, which can significantly reduce asthma and allergy symptoms. By providing a balanced, whole-house approach, the IAQ in homes can be controlled much more readily than using exhaust or supply only schemes.