How Does Outdoor Air Enter a House? - A Guide to Indoor Air Quality, Part Two

Welcome back to our Guide to Indoor Air Quality series! Last time, we talked about the causes indoor air problems. Now, it's time for part two...

So, How Does Outdoor Air Enter a House?

Outdoor air enters and leaves a house by: infiltration, natural ventilation, and mechanical ventilation.

In a process known as infiltration, outdoor air flows into the house through openings, joints, and cracks in walls, floors, and ceilings, and around windows and doors.

In natural ventilation, air moves through opened windows and doors. Air movement associated with infiltration and natural ventilation is caused by air temperature differences between indoors and outdoors and by wind.

Finally, there are a number of mechanical ventilation devices, from outdoor-vented fans that intermittently remove air from a single room, such as bathrooms and kitchen, to air handling systems that use fans and duct work to continuously remove indoor air and distribute filtered and conditioned outdoor air to strategic points throughout the house.

The rate at which outdoor air replaces indoor air is described as the air exchange rate. When there is little infiltration, natural ventilation, or mechanical ventilation, the air exchange rate is low and pollutant levels can increase.

Next in this series... What if You Live in an Apartment?

*Content provided by the Consumer Product Safety Commission and the Environmental Protection Agency. CPSC Document #450. This document is public domain.*