Vent requirements for bathroom exhaust fans


Old 05-03-04, 03:32 PM
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Vent requirements for bathroom exhaust fans

This concerns a completed project, as I was starting to wonder if the way I did it is acceptable:

I installed Panasonic ceiling exhaust fans (rated at 70 cfm) in my two bathrooms. The bathrooms are adjacent, so the fans are about 6 feet apart and approximately 5 feet away from the exterior wall. Knowing that the fans need to be vented to the outside, I used 4 inch flexible aluminmum duct exiting the exterior wall (as opposed to the roof) through a dryer-style vent. I ran the duct from each fan and connected it to a "Y" connector to reduce down to a single pipe going out through the vent. The vent exits the wall at a point that is about 3 feet above a window and about 3 feet below the roof overhang.

Does this set-up sound OK? Questions I have concern whether it was OK to install just one vent opening for the two fans and whether the vent proximity to either the window or the roof overhang raises any problems. (I have read that at least certain types of vents - e.g., drain vents - cannot exit a wall near a door or window and am not sure whether this applies to exhaust fan vents.)

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Old 05-03-04, 09:54 PM
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You did well, UNTIL you got to the wye. I would have 2 seperate vents going out the wall -- no interconnection between the 2 fans.
Old 05-04-04, 05:19 AM
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"My Two Cents"

Hello: Kray

I also do not agree interconnecting the two fans was such a good method. Each fan has an internal self closing baffle to prevent drafts from entering back through them. But not so they can be interconnected.

The bottle neck after the "Y" will also cause a reduction of air flow when and if both fans are on at the same time. But the internal baffle will prevent recirculation if only one fan is on at a time.

Sewage and drain vents cannot exit any other location except at the roof top to prevent sewage gasses from entering the house or structure. Which is why there is a code requirement to roof vent those lines.

Since the project is already done, the installation may work well. Mostly because the distances of the venting pipes is a short run length. However, the section passed the "Y" is still a reduction for the volume of total volume of air. 70 + 70 = 140cf.

Within this forum topic, will be already asked multiple questions on the subject of bath fan installation. Reading them may provide additional information.

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Old 05-04-04, 05:48 AM
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Wrong type of vent exhuast for you to worry about with clearances.

Wye connection will cause back pressure into other bathroom. Should be 2 seperate vents and terminations or internal baffles on wye. Vent run with flex can not be over 14 feet under 2000 IRC code. (check your local code for requirements)
Old 05-04-04, 08:58 AM
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Originally Posted by Sharp Advice
Sewage and drain vents cannot exit any other location except at the roof top to prevent sewage gasses from entering the house or structure. Which is why there is a code requirement to roof vent those lines.
Actually they can terminate out the sidewall with certain conditions; IE must be 10 ft from lot line, not under overhang wit soffit vents, grilled to keep birds from entreing & nesting, etc.

I'm not certainas to what plumbing code you usually use, here are some examples of various code references that permit wall venting:
P3103.6 in IRC,
905.6 in IPC,
3603.6 in IOTFDC,
3601.5.3 in CABO 1&2 Family,
12.4.5 in NSPC,
1404.5 in SBCCI,
P906.3 in BOCA.
Don't have a current UPC or IAPMO, but it only applies in CA (perhaps a couple of others, would have to go back and check) and anyway now it looks like the new gov in CA may order the state to go to the International codes in the not-to-distant future.
Old 05-04-04, 10:11 AM
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Hello: enigma-2

Thank you for pointing out all the specific codes which apply and all the possible variations which may also apply, from state to state, etc.

I was here in this question and often do reply (as many other moderators and members) using generic information. Highly technical information does have it's purposes. For members whom have a specific needs and or care to explore every finite detail(s) of any diy project.

Your expertise is welcomed. However, your directly quoting of my exact wording is not needed nor appreciated by myself or doing likelywise to other moderators and or members. Kindly refrain from doing so in the future.

Read the question and post your own best advice. Refrain from attempting to dazzle the public with technical information and or point out the inaccuracy of anyones replies posted to questions.

Any and all of such is not welcomed, needed and or appreciated.

If you have questions, etc, send me a PM!

Kray: (notuboo & lefty)
Kindly excuse this public interruption reply post.

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Old 05-04-04, 11:10 AM
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Thanks to everyone for your input. Both fans are rarely in use at the same time, so my arrangement seems to be working. But fortunately, this is a relatively easy matter to address by adding another vent opening when I have a free afternoon so I will plan to go ahead and do that.
Old 05-04-04, 07:53 PM
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I will have to admit, I have done this once, and only once for a customer because the pitch of the roof was a 1/12 or 0/12, and the customer refused to put more than one opening in the roof.

I ended up using 3" SCH 35 piping along with fittings transitioned to the 130 CFM fans. All the pipes were installed for free flow with a wye turned upside down right at the roof connection to catch the two.

Even though the two fans had baffles in them, and the roof vent itself had a baffle with a mesh shroud to finish off the outside application, when I was finishing the wiring in one of the bathrooms, someone took a dump in bathroom number one, homeowner walked into the bathroom I was in and thought I left a mess in his toilet. Wasn't me. I shall not tell a lie.

The air venting from fan number one instantly goes back to baffle number two and allows odors to enter another bathroom.

That, is the drawback of connecting two fans together, and the customer surely couldn't blame me, I told him that this was a possibility, and sure enough, it did.

If you connect them, you can instantly move moisture or smells right to the other bathroom in this fashion.
Old 06-08-04, 06:43 AM
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I have a situation very similar to the original poster, except I don't want to exit through the roof since it is on the front of the house, and I don't want two hoods on the side wall. I hooked up two Panasonic fans through a wye, and, as expected, when one is on, you get a little bit of air flow out through the other one. The Panasonic baffles are not fully sealed backdraft preventers. Would putting a spring loaded backdraft damper like the fantech one linked below keep air, humidity, and odors from getting out through the other fan?

What about a cape backdraft damper, like the Tamarack? They claim at most 2cfm of leakage at moderate pressures.


Last edited by abm760; 06-08-04 at 10:48 AM.
Old 06-08-04, 11:22 AM
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There are vent heads for fans made to go out and down right in the overhang or soffit of a home. That you can use if you dont want to go through the roof. TOO each his own. Dont Y them.


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