Advice on bath exhaust vent termination.

I wanted to ask your opinion on the duct termination for my 2 bath exhaust fans.

The question I have is for the termination of one of the fans. It would be easier for me to cut through my cedar siding to do a side wall termination. It would be about 12 -15 feet total vent length. If I did the roof I would need to hire someone to vent through the roof(About 3 feet)

The fan is a Broan Model 683 CFM 80

Not sure of the maximum length of vent.

For sidewall application.
Would you slope vent up slightly or run on attic floor?
What type duct would you use? Flex, semi corrigated metal?


Dave…side wall vent should be fine with that fan and why cut another hole in the roof…15 feet should be no problem with which ever material You choose to work with
just make sure You have a check valve in there for back flow wind and I would say across the floor is fine…

Also, running them out a sidewall with rigid duct buried in insulation to prevent condensation is good.

The distance run would depend on the size of the bathroom and cfm of fan but, like Jim said, it should be okay.

Hi David
I would suggest the easiest install
12-15 feet is not too long and I would also use a flex it’s easier to maneuver around. [FONT=Comic Sans MS]I would also recommend arching the flex piping to prevent water intrusion at termination. [/FONT]

Personally I prefer sidewall termination.

Thanks, I appreciate the feedback.

I like either way but if the sidewall is what you can do that’s what you should do. I like the idea of it being insulated and the sidewall is the easier way of doing that especially if you have blown in. I also prefer the caps with the three louvers.

The vent installation went very well today and thanks to you guys I saved a few hundred dollars.

A roofer wanted a minimum of $350. It cost me around $100.

I attached a few pics of the install. I just want to insulate the exposed pipes in the attic and patch my siding as I had to close to a window.

The hole saw combo worked great and seems to be of good quality.

I am going to post the inferior fan set up that was there before, leaking at connections and molding the wallboard. (I am ashamed to admit I was the dolt that installed the 1st fan about 7 years ago.

Thanks again!!

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I would vent it into the attic (I know you aren’t supposed to) before I would put it out the roof. That would be a leak waiting to happen!

Not if properly flashed like any other roof penetration, (sewer vent, furnace pipe, etc.).

So properly flashed penetrations never leak? What is the life span of the flashing or the metal or plastic vent?

That’s a good question; you would think that metal for the most part would out last the plastic vent cover by far and a few years ago that may have been true, but with the improvements they have made with plastic materials it’s hard to truly say.
I would suspect the life expectancy of the plastic vent cover would be determined on the extreme weather conditions it had to endure, quality of the plastic used and location.

And David
I personally would still arch the last few feet of the flex vent piping above the termination point (vent cover) this will help prevent any possible chance of water running back into flex piping in the event of water intrusion. Just a thought.

Gable ends, sidewalls and eaves are always the preferred method of termination. Only as a last resort do our technicians install venting thru the roof.

Just an observation but the last few ft. of the pipe should be wrapped with insulation condensation will occur.Warm pipe cold attic air…

And the best practice is to slant horizontal runs of duct down toward the exterior outlet to drain any condensation outside, just saying!

If the total length of exhaust pipe is in the cold attic above the insulation, it should be insulated for its length to prevent interior condensation. I have seen a water filled droop in a flexible plastic pipe that blocked all ventilation. There was about 3/4 quart of water.

If the pipe is run in a heated space, then the last 3 feet at the exterior wall should be insulated with an airtight vapour barrier over it to prevent condensation on the exterior of the duct and consequent dripping. Small amounts of cold air bypass the damper into the duct or the air in the duct become cold (not an insulted damper) and condensation on its exteior occurs.

I be darned if I would of went 15 ft to a side wall with a roof within 3 feet $350.00 for a roofer to do what cut a hole in the roof and install a rain cap duh I would have taken the roofer on the roof and pushed him off and screamed $350.00 just as he hit the ground.
Roof vents of some nature are installed on every roof out there what is the big deal about another one. Sometimes you guys advice is off the wall pun intended

Well said. On Monday I inspected a house with a decent quality range hood installed. It ends there.

The installer went against the manufacturer’s instructions of 6" diameter (28.3 sq in) or 3 1/4 X 10 (32.5 sq in) ducting. He installed 4" diameter (12.6 sq in) spiral wound aluminized ducting, essentially dryer ducting. It was about 20’ to a side wall while a roof vent would have about 3-4’ of duct.

Spiral wound duct acts like ducting of 1 size smaller, so this 4" duct is performing like 3" (7.1 sq in) straight smooth duct! So this is essentially a working condition that is 75% smaller than recommended.

It was uninsulated through a cold attic on top of the insulation batts.

Like I said, a decent medium quality range hood only. Wonder how well that will work?

I have the insulation and plan on insulating the last few feet of exposed pipe. I did the other pipe about a week ago.

Yes, I could of done a better job with that, so I guess it is not the best practice.