# Separate Exhaust for Toilet Room



## dchin (Feb 24, 2010)

I am working on a small 800 sf T.I. in a two-story office building in New Jersey, converting the space into a dental office. There is an existing toilet room exhaust fan (controlled by switch) that has a duct leading into a cmu shaft that leads to the roof. We are adding an exhaust fan for the lab area (also controlled by a switch) and an exhaust fan in the mechanical closet, controlled by a thermostat.

My mechanical engineer thinks that the two new exhaust fans cannot exhaust into the existing toilet room exhaust duct, but must be separate.  IMC 401.4.1 is vague on this - " the exhaust from a bathroom or kitchen in a residential dwelling shall not be considered to be hazardous or noxious contaminant," so my engineer's thinking is that a commercial toilet exhaust would be hazardous.

The DCA official she spoke to said that there is a possibility that if the exhaust systems were combined, there is the possibility that the toilet exhaust could enter the other spaces if the other exhaust fans are 'OFF".

It will be a lot of work to install new exhaust ducts to the roof, and I would like to know if others have run into this situation.  Could the exhausts for the two new fans at least be combined?

Thanks, - Donald


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## dchin (Feb 24, 2010)

Re: Separate Exhaust for Toilet Room

architect

really odd, but when I type "Arch----t it comes out as "man with pencil who draw". Practical joke?

Donald


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## Coug Dad (Feb 24, 2010)

Re: Separate Exhaust for Toilet Room

A$rchitect always comes out at man who draws with pencil.  Long standing inside joke.  There is also one for persons who practice the law.


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## Coug Dad (Feb 24, 2010)

Re: Separate Exhaust for Toilet Room

It sounds like the condition you describe would allow the exhaust fan in one toilet room to push the air into the other toilet room if that fan were not running.  This would not be within the intent of  the code.  A common fan would probably be OK.  I also wonder if back draft dampers would address this concern.


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## TJacobs (Feb 24, 2010)

Re: Separate Exhaust for Toilet Room

Coug Dad nailed it.


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## MarkRandall (Feb 24, 2010)

Re: Separate Exhaust for Toilet Room

Three exhaust fans combining into a single exhaust will not work. The official you spoke with is correct except it's not a "possibility", it's a sure thing that exhaust will not all be exhaust out of the building.

A common inline exhaust fan with correct duct sizing should be okay (fan located after ducts are combined). This will probably still require new ducting to the exterior as the existing duct is probably not large enough.


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## Dr. J (Feb 24, 2010)

Re: Separate Exhaust for Toilet Room

There is no prohibition against combining toilet exhaust with other exhausts, but the practical issue with forcing air from one exhaust into another is valid.  The backdraft dampers on those fart fans are pretty useless.

"Hazardous" exhaust is defined in IMC 510.  Toilet exhaust is not hazardous (not even my teenager's bathroom).

The code issue to be concerned with is 601.4 "_Exhaust ducts under positive pressure, chimneys, and vents shall not extend into or pass through ducts or plenums._"  Is this space plenum return?


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## dchin (Feb 26, 2010)

Re: Separate Exhaust for Toilet Room

Thanks for all your replies and advice. The space above the ceiling is not used as a plenum return.

Donald

p.s. lawyer - I had to try it out.


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