Attaching 2 adjacent bathroom fans with a Y

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Posted by: from Kirkland
10/14/2012 at 10:50:29 AM

I'm currently renovating our M bathroom and added a Panasonic whisper fan in the ceiling, this bathroom is close to another bathroom that currently has the same Panasonic whisper fan and was wondering if it was a good idea to attach them together with a Y tube so that I do not create a second hole in the roof.

Now that both fans are connected I noticed condensation from one bathroom tends to go to the other. My reno guy thinks we should add clapets (term used in french) in the tube in order to stop the transfer of air.

Can anyone tell me if it is a good idea?? Will it become a problem down the road?? Other suggestions are welcome. Or do I go ahead and do the 2nd hole in roof?? Something I would like to avoid..

Kind regards,


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Robert from Electrilight Ltd. in Oakville
Date/Time10/14/2012 at 12:10:12 PM

Both fans require an exhaust through the wall or roof, otherwise it will cause airflow problems and returned moisture to sit in the duct not used. A flow chamber (or flapper as you call it), will only further the problem as the more powerful fan or airflow will restrict the second from evacuating air.

Example: a 110 cfm requires a 4 inch duct not a 2" (which is what happens when you double the fans on a duct line), unless you replace the line after that "Y" to a 8" duct all the way out.

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Date/Time10/14/2012 at 12:13:38 PM

You never want to connect two vents on the same exhaust line because it will back vent to one not in use. Proper HVAC guidelines require a minimum of a 4" exhaust duct per fan. Some larger fans require a 5" exhaust. Make sure when cutting the roof vent not to over cut shingles. When buying pipe exhaust buy the proper damper type for roof and transition pieces for the duct. Hard pipe is recommended with insulation wrapped from fan to underside of roof instead of flex hose.

Hope this helps

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Date/Time10/14/2012 at 12:24:24 PM

It is not recommended to connect more than one exhaust fan to an exhaust pipe. If you are concerned about another hole in the roof you could look at installing a soffitt vent.

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Karim in Kirkland
Date/Time10/14/2012 at 2:40:20 PM

Thanks guys, this is very helpful.

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Date/Time10/14/2012 at 6:21:37 PM

It is against the building code in Ontario to join two fans together. The easiest route is rarely the proper way of doing things. If you want to elimnate problems of condensation between bathrooms then vent both exhausts independently.

If you were looking for an easy way out then you could have bought a commercial grade exhaust fan and hooked it up to both bathrooms, using one fan to exhaust both bathrooms. The only issue with this is the heat loss which would be considerable with the amount of air changes you will have occurring every time you use one bathroom.

My advice is to exhaust each bathroom separately and enjoy the beneftis of a proper exhaust system.

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Date/Time10/17/2012 at 10:06:46 PM

I have done this before, not me but an HVAC trade i had working for me on a new home construction project i was managing. The bathroom was located in an area that was not convienient to vent through the roof or exterior wall because of a patio.

The HVAC contractor vented the exhausted fan into a vented portion of the soffit. Eliminating the need for a roof vent, and also an exterior wall vent. This application was inspected by the city and passed.

I am sure there are certain applications where this may be allowed or not allowed, but in this instance and this town, and this inspector it was ok. So that may be an alternative to cutting a new whole into your roof.

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