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Venting bathroom fans #5112658 05/22/19 05:59 PM
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Donald Offline OP
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All of my bathroom fans are vented into the attic not to the outside. A new roof goes on tomorrow so I am having roof vents installed. But I have only found two vent hoses in attic. I have three bathrooms each with fan.

Is it common and acceptable to put in a "T" or "Y" and vent two bathroom fans with one hose?

Do I have two or three roof vents installed?


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Re: Venting bathroom fans [Re: Donald] #5112676 05/22/19 06:13 PM
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dishdude Offline
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Have three installed and cap it off until you find the third. Using a T or Y will restrict airflow and reduce effectiveness.


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Re: Venting bathroom fans [Re: Donald] #5112677 05/22/19 06:14 PM
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I believe the code call out for venting to atmosphere for all bathes that have a tub/shower.

Re: Venting bathroom fans [Re: Donald] #5112681 05/22/19 06:16 PM
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satyr64 Offline
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If the fans are in the bathroom ceiling then each need there own hose/roof vent. If they were tied together then when fan 1 is on it would blow air out the vent and the back into other tied bathroom fan 2. Only way around this is if you had a fan in the attic with the Y placed before the fan. Bet the other fan has hose under insulation or it was ripped off/never connected. Get three vents installed tomorrow above each bathroom and hookup the lost one later.

Re: Venting bathroom fans [Re: Donald] #5112720 05/22/19 06:46 PM
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pbm Offline
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I would think that venting a bathroom into the attic would affect your insulation due to moisture....that's why I ran a flex vent to a roof vent when I installed my bathroom exhaust fan.


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Re: Venting bathroom fans [Re: pbm] #5112753 05/22/19 07:15 PM
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Skippy722 Offline
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Originally Posted by pbm
I would think that venting a bathroom into the attic would affect your insulation due to moisture....that's why I ran a flex vent to a roof vent when I installed my bathroom exhaust fan.


It does... learned that the hard way.


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Re: Venting bathroom fans [Re: Donald] #5112850 05/22/19 08:40 PM
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Donald Offline OP
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From running fans and feeling the flow from vent hoses I could find, it seems the two bathrooms with shower/tub have vent hoses going to the attic area.

The half bath on the first floor does not seem to have a hose going into the attic area.

I felt between the floor joists for a hose or similar as far in as I could stick my arm.

No noise from the first floor fan that I could hear in the attic area.


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Re: Venting bathroom fans [Re: Donald] #5112876 05/22/19 09:12 PM
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Wolf359 Offline
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That's not code. Basically whenever you see people vent their bathroom to the attic, you usually also find mold.

Re: Venting bathroom fans [Re: Donald] #5112896 05/22/19 09:40 PM
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Dinoburner Offline
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First floor vents usually vent straight out the side of the building. Pull the fan assembly down and with a light and mirror you might see where the hose goes. Have seen where contractors never penetrated the wall. It is code that all vents must communicate with outside air.


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Re: Venting bathroom fans [Re: Donald] #5112905 05/22/19 09:48 PM
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We vent our bathroom through the attic and out the gable vent with a flexible tube.

Re: Venting bathroom fans [Re: Donald] #5113028 05/23/19 01:36 AM
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spk2000 Offline
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I was forced to fix these when I sold a house from the late 80's and new codes didn't allow for venting into attic but at the time it was considered acceptable. Only had this house one year and when I had a home inspection done they missed this along with multiple other items.


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Re: Venting bathroom fans [Re: Skippy722] #5113122 05/23/19 06:47 AM
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Driz Offline
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Originally Posted by Skippy722
Originally Posted by pbm
I would think that venting a bathroom into the attic would affect your insulation due to moisture....that's why I ran a flex vent to a roof vent when I installed my bathroom exhaust fan.


It does... learned that the hard way.



Yea, definitely not a old thing down the road🤬

Re: Venting bathroom fans [Re: Donald] #5113128 05/23/19 06:50 AM
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dadto2 Offline
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Originally Posted by Donald
From running fans and feeling the flow from vent hoses I could find, it seems the two bathrooms with shower/tub have vent hoses going to the attic area.

The half bath on the first floor does not seem to have a hose going into the attic area.

I felt between the floor joists for a hose or similar as far in as I could stick my arm.

No noise from the first floor fan that I could hear in the attic area.


Our first floor 1/2 bath vent goes down the wall and under the floor to the outside wall of the building, where it's beside the dryer vent. Can you look in the basement to see if it's there between the joists? (My house was built in 1968. Maybe that was common in that era)


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Re: Venting bathroom fans [Re: Donald] #5113395 05/23/19 11:23 AM
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You have to be careful routing exhaust fan hose/pipe in areas that are going to get cold. Condensation will build up and eventually drip somewhere. I've used 4" plastic pipe and under soffet outlet vents. Pitch the pipe towards the outlet.

Donald, I hear you on the "Teed" together fans. My two upstairs bathrooms are like this. They are tied together somewhere buried in blown-in attic insulation and exit through one vent out the siding. There are dampers (like a check valve) in each fan, so if anything, only a tiny bit of flow will bleed from one fan to the other. Best I can tell from the outlet, it's the cheap white corrugate vinyl hose too. I hate it, but it's working and going fishing through the attic trusses in a sea of blown in insulation isn't something this old dude can easily do.


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