Image Credit: All images: Bath Fan Solutions
More Musings of an Energy Nerd
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…
Weekly Newsletter
Get building science and energy efficiency advice, plus special offers, in your inbox.
This article is only available to GBA Prime Members
Sign up for a free trial and get instant access to this article as well as GBA’s complete library of premium articles and construction details.
Start Free TrialAlready a member? Log in
8 Comments
First Professional Grade Installation System
Martin: Thanks for the review of our new fitting. After years of investigating problems associated with the 'installation' of; and associated 'call backs' with the current selection of soffit mounted vent fittings, I felt it was time to develop a real professional grade installation system. The current selection of soffit terminations do not address the actual building sequence for installing a bath fan, ducting and fitting at a soffit location. This system was developed to solve several problems:
a) The fan installer can now complete the entire system (pre-soffit) in one trip with lower total cost
b) A better overall installation leads to better air flow improving customer satisfaction
c) The built in air-tight damper improves Blower-Door test results and reduces cold weather comfort complaints due to cold air entry at the fan(s)
d) Soffit discharge location does not require water intrusion protection (flashing) as does roof or wall discharge fittings
e) Flush discharge grille is aesthetically more attractive than other options
Spot ventilation in bathrooms is more important now than ever. It's time the process was improved for fan venting at the soffit location. We are currently working on several other new products.
For more information readers can go to our website: http://www.bathfansolutions.com
I know this article is 5 years old but I am searching for a soffit vent solution for my bath fans. My concern with this design is that moist humid air can be drawn back into the soffit vents and enter the attic despite the moveable grill. Does anyone have any real world experience with this particular soffit vent?
Otosan,
If you exhaust it close to the fascia, and use a directional vent termination, moist air doesn't get drawn back into the attic.
I've got three of them on my soffits, two bathroom exhausts and one for the dryer. On cold days I can clearly see where the moist air goes, and it dissipates well away from the house.
Hello Malcom,
Thanks for your reply.
That is good to hear of your experience.
Do you mean that you have three of the EZSoffitVents (mentioned in the original post) or three of another model, like the picture in your post?
Do you have any information about the vent that you posted a photo of?
Thanks.
Otosan,
I have three of the one's I posted. They are called Soffit or Under-Eave vents. A few manufacturer's make them. Lambro, Heyoka and Dundas-Jafine - and probably others too. You can find them in any of the big-box stores.
Thanks Malcolm, I'll do a search.
Otosan,
None of them seem particularly well made, but they are cheap, so I see them as replaceable.
One of their advantages is they have no screens, so they can be used on dryers too. I've never understood why some vents with flappers also have screens. It would take a pretty powerful insect to fly up a vent while it was exhausting 50+ cfm.
I guess you're right. I always supposed the heavier screens were to keep out birds, bats and squirrels. They can easily lift a flimsy flap. But squirrels and raccoons could chew through the plastic as well if they wanted.
You live in the North West I believe. I've seen photos of these types completely frosted up in prolonged cold snaps. Have you had any problems with the damper freezing shut? I wish these extended past the roof line at the eaves. I'd feel more comfortable about exhausting the vapor away from the soffit intakes.
Log in or become a member to post a comment.
Sign up Log in