I am installing an exhaust fan in my upstairs bath. An easy and close by exhaust source would be the existing plumbing vent.

Can I tee into this vent without worrying about odor problems in the bath? I would tap into it just below where it goes through the roof. The existing vent is close to the peak of the roof. I would guess that down drafts which might push gases back towards the exhaust fan wouldn't be much of an issue. Even if there were down drafts, the closeness of the tee to the vent opening should mean that it was fresh air being pushed back. Also, the fan has a flap valve which should keep air from coming back in when the fan is off.

I would also plumb the exhaust fan pipe so that it had enough slope coming into the side of the tee to prevent rain from finding it's way into the fan.

NO, NO, NO . Do not do this. This is a code vialation in every state and in every part of the world. The exhaust vent for your bathroom MUST exit separately from the house. You can not tie it into a plumbing vent. It may seem like an easy solution, but it is not a solution at all.

Once again, DO NOT DO THIS. If you have further questions as to how to properly vent the exhaust fan, please let us know. We will try to help you do this properly, and keep you safe.

I was afraid that might be the answer. Oh well, I guess it's time to get out the sawsall and whack another hole in the roof.

Thanks for your reply.

Look at all other possibilities. Do you have room to take the exhuast vent out through the side of the house. If so, it would be much easier. This way you wouldn't have to cut another hole in the roof, Just get a 4" hole saw bit, and terminate through the side of house in the attic. Ive posted a pic of the termination kit for sidewall.


If this is not an option for you, please let me know more about your layout, and I will try to make this as easy as possible. Good luck and take care.


Lee.

The bath is located upstairs in a cape with a rear 3/4 dormer. Normally such a bath would be located on the rear of the house and your suggestion would work. In my case the bath is on the front side of the house, so there is just the sloped roof above it. Yeah, it's a weird layout, but, my house is longer (front to back) than a normal cape, so it works. I will either vent it up through the roof on it's own pipe or through the attic to the gable end. This would be about a 15 foot horizontal run. Is that excessive?

It would be better simply to terminate the fan in the attic, (much better to run it out thr roof then to connect to a plumbing vent. Connect to a vent would give you a direct connection from your house to the city sewer allowing sewer gas to enter your home, sewer gas's a health hazard to your family and the methane content makes it explosive. Regards, Tom

If there is an eave, you can mount one of these (post #4_) upside down in the top of the eave. Just remember to put a check valve in the pipe.

There is always a way to terminate fan vent...

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Originally Posted by KeepItSimpleStupid

If there is an eave, you can mount one of these (post #4_) upside down in the top of the eave. Just remember to put a check valve in the pipe.

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KISS, There's a flap in the vent treminal, (see image) that closes and acts like a check valve when the vents installed right side up. I've never seen one installed upside down. Regards, Tom

Well, I'll show you one. My father did it. And the flap stays open and there is no check valve. I need to add one.

I really don't have a problem with it EXCEPT for the lack of a check valve when installed upside down.

KISS: "Check Valve " ? Can you explain what kind of check valve on exhaust vent are you talking about ?

Usually bathroom exhaust fans have a flapper(check) built into the vent adapter.

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Originally Posted by speedball1

It would be better simply to terminate the fan in the attic, <snip>

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Terminating a bath vent inside an attic is not allowed by code. It must go outside, and if you have to pay heating bills, make certain that there is some kind of automatic damper in the line. The one that comes with the vent fan and the flapper in the exhaust hood are usually all you will find and they are minimal.

We know about the usual flapper thing, but I remember seeing a stand alone check valve that can be used.

While I was searching the Internet today, I did find a bathroom fan soffet vent kit that DID NOT have an integral check valve.

I'll keep looking.


I found the soffet vent for a bathroom fan. It mounts upside down and contains an integral "backdraft damper".

This would work for me too.

http://www.heyokasolutions.com/White...prmx-sv401.htm

Where did you find that? I've only seen the kind with no damper.

Seems like I forgot to post the link:

White soffit vent for 4" ducting with backdraft damper

Thanks.

What do you think of it?

Looks like it should work, but the footprint is a little bigger (7"x7") than I would prefer.

Thanks!

Here is even a better vent, but there is no mention of a backdraft damper.

Master Flow 4 In. Eave Vent for Bath Exhaust - 12 per Carton - BFEV4 at The Home Depot

I don't think you need damper or "check valve". The fan should have a damper already built in.

The Master Flow 4" vent hood is all you need...

Here is a separate backdraft damper.

4 Inch Duct Spring Loaded Backdraft Damper - RSK4 - 4" - 16" Spring Loaded Backdraft Damper