Filters warped or bent by air suction. Worn gaskets in the filter frame. If any open spaces exist among the filters, unfiltered air will happily take that route. As a standard part of every cleaning, ensure the filter rack is not a Swiss cheese of gaps and holes. If you spot errors, fix them or call the problem to the client's attention.
Poor Filters Discussing filter preferences is almost like talking religion or politics.
Almost everyone you speak with has his own opinion-particularly filter salesmen. This is especially true for the range of filters applied in the residential and commercial market. For residential areas such as apartments, dormitories, and motels the recommended rating is 20-30 percent or better. Hospitals should have at least a 90-percent rating. Higher-efficiency filters slow down the air flow and cause the fans to work harder because it's tougher for air to go through them.