Re: Roof Vent for muliple washroom vent fans -- Ask the Roofing Sider Forum

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Date Posted: Thu, Nov 07 2002, 6:38pm
Author: A Roofer
Subject: Re: Roof Vent for muliple washroom vent fans
In reply to: Paul 's message, "Roof Vent for muliple washroom vent fans" on Thu, Nov 07 2002, 8:22am

You kinda got me thrown for a loop with the term vent fan and PVC piping in the same use. Vent fans are usually vented using duct work and used for exhausting dryers and bathroom fans. They do require their own separate vents or else when one fan tries to exhaust it will blow into the other's vent. Anything that exhausts needs it own vent for this specific reason. If your PVC piping is for plumbing drainage you will probably be just fine tying them together. They are there to allow air into your plumbing system so it doesn't gurgle as it drains. If you have ever seen a drain that gurgles or drains slow its because they don't have an air inlet that is usually stuck through the top of the roof. Its like when you have a full glass of water in a sink then turn it upside down and lift it out of the water and the water remains in the glass until it gets high enough just out of the water so air can draw in and replace the water in the glass. Unless it is possible that all three of these drains might be in use at the same time the existing plumbing vent coming out of the roof should be sufficient enough air supply for your plumbing to drain properly.

Either of these things are simple things to do and the costs should run between $200 to $500 to add three vents out the top of the roof.

Hope this helps,
Tim Soth / A Roofer

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Replies:

[> [> Re: Roof Vent for muliple washroom vent fans -- Paul, Fri, Nov 08 2002, 6:52am

Hi. Thanks so much for your info. It is not uncommon to use 3 or 4 inch PVC piping for bathroom fan applications. The flexible hosing has a greater chance of leakage and humidity and roof trusses don't mix. My hope was to use an upside down Y fitting that would prevent the exhaust from one fan to go down the pipe of the other. Plus I figure most fan must have some kind of closure to prevent outside air from coming inside. The only drawback that I could think of initially is that I might have 3 fans all trying to push air out of the same 3 or 4 inch hole. But then I figured if the the fans were small in size that maybe this was possible. My idea seemed so logical but I certainly understand and appreciate the information you gave me.

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