Exhaust fan for restroom

[newmep]

Hi,
I need help finding litrature and advise on design of a central exhaust system from large public restrooms. Each facility has about 10 sanitary fixtures. 75 cfm per fixture is my target. Restroom is on first floor and exhaust must be thru roof on 3rd floor. Would the fan go on the roof or is it better to place fan above cieling-if there is space.
thanks,

 

[richiekpr]

most probably the best arrangement would be to horizontally, with ductwork, connect exhaust grilles sized and purchased for 75 cfm service onto to a vertical duct in hopefully some shaft built into the structure up to the roof where the fan should be some centrifugal. either a dome type or utility set. sounds like a dome type should be adequate for your application. greenheck, loren cook, twin city are fan manufacturers and if you reach them they may put you in contact w/ their local sales rep.

 

[CountOlaf]

There are plenty of fan manufacturer's for standard exhausting requirements no matter where you want to put the fan. The fan rating (size) will be based on two main characteristics: the flow rate (which should just be the sum of your CFMs which you seem to have a good grip on) and the static pressure, which you'll have to add up for the various system components (duct lenght, size, grilles, etc.).

Regarding the inside/outside thing, ideally, you want the fan outside, but as a compromise, if you have to (or want to go inside) try to keep it in the 3rd floor ceiling space near it's point of discharge to the outside. The reason for this is that way all (or most in the compromise situation) of the ductwork will then be under negative pressure throughout it's run through the occupied spaces. If there is a leak (and ductwork is rarely air-tight), it will draw air into the duct rather than discharge odorous air into the occupied areas.

The total external static pressure of your system should not be different regardless of the fan's position in the system (at one end or the other or somewhere in between).