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:
- Leaky duct seams;
- Duct diameters that are too small;
- Convoluted ducts with unnecessary twists or too many elbows.
Other problems aren’t necessarily the installer’s fault:
- Most fans lack a good backdraft damper. Installing an inline backdraft damper severely restricts airflow, however.
- In many homes, there is no easy way to route the exhaust duct to an exterior termination. While soffit terminations are tempting — and in many cases closer than a gable-end termination — most existing soffit termination hardware has serious problems.
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…
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