Comments on: Installing an Exhaust Fan During a Bathroom Remodel

By: Allison Bailes

Allison Bailes — Wed, 28 Sep 2016 00:31:02 +0000

Armand, the nice thing is
Armand, the nice thing is that this fan came with a 6" takeoff.

By: Armand Magnelli

Armand Magnelli — Wed, 28 Sep 2016 00:25:23 +0000

Allison, I only provided the
Allison, I only provided the chart to highlight the difference in resistance between the duct types. Using 6 inch duct for a straight run such as yours obviously gives you a huge margin for error. In your case, I may have used 6" flex as well.

By: Allison Bailes

Allison Bailes — Wed, 28 Sep 2016 00:07:52 +0000

Bob, that's more than just an
Bob, that's more than just an exhaust nightmare. That house sounds dangerous. Venting a furnace into an attic space? Wow!

By: Allison Bailes

Allison Bailes — Wed, 28 Sep 2016 00:03:42 +0000

Paul, I didn’t show a photo,
Paul, I didn’t show a photo, but I did mention in the article that I insulated the duct. I took the photo you see just to show the flex duct pulled tight. And you’re right. It was pulled tighter once I fastened the left side with the zip tie after sliding the insulation jacket over it.

The duct is 6″ and it reduces to 4″, so that does give it some extra velocity.

By: Allison Bailes

Allison Bailes — Tue, 27 Sep 2016 23:48:29 +0000

Armand, Yes, indeed. I’m not
Armand, Yes, indeed. I’m not as good as I was back when I built a house and then was a home performance contractor, but I still know how to do stuff with tools.

Prescriptive charts like the one in your link are good as long as you pay attention to the small print at the bottom. For bath fans, that’s really all you need.

The duct coming off the fan was 6″ and I had to reduce it to 4″ to go through the band joist. That was all the space I had.

By: Allison Bailes

Allison Bailes — Tue, 27 Sep 2016 23:39:44 +0000

Sean, yes, I think it
Sean, yes, I think it probably does. As you can see in the 5h photo, it hangs down and blocks most of the duct when the fan's not on. I haven't measured sound levels from outdoors with and without it, though.

By: Allison Bailes

Allison Bailes — Tue, 27 Sep 2016 23:38:00 +0000

Sean, To go through the wall
Sean, To go through the wall instead of the band joist, I would have had to put in two 90° elbows and give up more space for insulation. Plus, it would have been more visible on the exterior wall, perhaps bringing me some grief from the homeowners' association, and it would have meant cutting through more brick. That fan with the rod sounds like a good way to ensure good air flow. Probably not insulated very well, but with no duct, the air flow must have been close to the rated number.

By: Sean

Sean — Tue, 27 Sep 2016 22:08:10 +0000

Allison, could you have
Allison, could you have placed the exhaust fan high on the exterior wall when you had the wall opened up? That might have simplified installation. You wouldn't have to cut through the rim joist. I don't know why exhaust fans come with such pathetic back flow dampers. It seems out of place in this age of air tight homes. The best exhaust fan I ever used was in my mothers vacation trailer. It was on the wall just above the stove. You pushed a rod that opened a water tight cover on the outside wall. The fan would then start. When you were done, just pull on the rod and the fan would turn off. The thing was air tight, even on the coldest days. Worked for 40+ years.

By: Sean

Sean — Tue, 27 Sep 2016 21:47:19 +0000

I wonder if the "Cape Damper"
I wonder if the "Cape Damper" Allison used would attenuate incoming sound. That would be a nice bonus.

By: Armand Magnelli

Armand Magnelli — Tue, 27 Sep 2016 20:26:44 +0000

Nice article. Great to see
Nice article. Great to see that you can do real work Allison. I’ve often used the chart available through this link to discuss the differences in air flow between flex and smooth duct. https://www.bpa.gov/EE/Sectors/Residential/Documents/BPA-W-exhaust-fan-prescriptive-duct-sizing.pdf Compare 4″ smooth and flex at 80 CFM. The difference is staggering.

I’m guessing that you used 4″ flex duct and the length appears to be about 3′. Is that accurate? It also appears that you transition to a smaller diameter fitting for outlet, but that may just be my misinterpretation of the photo.

Regardless, I would always try to use smooth duct when possible to maximize air flow.