Air sealing is often associated with improving the energy efficiency of heating and cooling system. But there are other even more important benefits.
Many of the cracks and gaps that let outside air in a house are located at the joints in the ceiling to the attic or on the floor over the crawlspace. That means the air leaking into the living space of a house can be coming from the attic or the crawlspace.
Unfortunately, the attic and the crawlspace are typically not the cleanest areas. They are often dusty. Rodents and other pests may live and die there and leave droppings. Crawlspaces can be wet. Leaks can also occur around fireplaces and other flues which are sources of soot, smoke and other toxic gases from combustion. So the air entering the living space from these cracks and holes can contain pollutants, contaminants, bacteria and excessive moisture, all of which can be detrimental to your health.
Sealing the leaky spots leading to the attic and crawlspace will stop the unhealthy air from entering the living space.
There can be holes and cracks on exterior walls and window frames which can leak outdoor air in. Fresh outdoor air is most often high quality air. It certainly beats the foul air coming from attics and crawlspaces. There are exceptions such as high pollens during certain times of the year or occasional high smog days. However, sealing these will let you have better control of when and where to let outdoor air in (e.g. by opening windows) and improving heating/cooling efficiency.
In addition to the health benefits, air sealing can reduce hot and cold spots and drafts inside a house, thus improving the comfort of the living space.
Once a house is well air-sealed, make sure that there is adequate supply of clean fresh air. This can be achieved by installing a mechanical ventilation system (which includes a filter) or opening windows when weather and external air quality permit.
