Most bathroom exhaust fans are installed poorly. Because of twisted ductwork, improper terminations, and (in some cases) inappropriate backdraft dampers, the actual air flow through the exhaust fan is much less than the fan rating.
In an article called “A Failure That Stalls the Certification of Many Energy Star Homes,” Allison Bailes described an Energy Star builder who installed nine exhaust fans, each rated at 110 cfm. The builder was hoping that these fans would meet minimum program requirements — requirements which call for bathroom exhaust fans to have an air flow rate of at least 50 cfm. When tested, however, only five of the nine fans met the minimum 50 cfm threshold.
Some of the problems with current installation procedures involve old-fashioned sloppy workmanship:
Other problems aren’t necessarily the installer’s fault:
In my article on bathroom exhaust fans, I recommended against soffit terminations: “Soffit terminations grow icicles during the winter, and allow humid air to be sucked into the attic in all seasons.” I may have to change that recommendation, however, in light of a new type of soffit termination that has been engineered to solve several bath fan installation problems.
The new soffit termination is called the EZSoffitVent (yes, with all the letters smushed together, without any spaces).
Designed for job-site realities
The EZSoffitVent limits the problem of humid air entering soffit vents by including an adjustable ring that allows the installer to direct the airflow downward at a 45 degree angle, away from the building. Air leakage when the fan is not operating is effectively prevented by a well-designed backdraft damper. The rigid plastic damper is hinged at the top. When closed, it’s fairly tight. Yet a breath of air from your mouth is sufficient to open the damper.