HVAC (Heating, Ventilation, Air Conditioning)

Wednesday, June 21, 2006

Toilet Exhaust

I found this toilet exhaust in a hotel room. For bigger bathrooms it is a good idea to have a separate exhaust over shower/tub too; this way you would avoid moisture spreading in the bathroom and fogging the mirror.
In the case above it was a small toilet and just one air intake served the whole area. See how the exhaust goes to a shaft accessible from the corridor (on the other side). Toilet exhaust is generally designed for 10 air changes per hour (or one air change in every six minutes). To compute the required air flow, calculate the volume of the toilet (lengthXwidthXheight) in cubic foot and then divide that number by 6 minutes, this would give you the required air volume flow rate in cfm (cubic foot per minute). Make up air (the same amount that you are exhausting) must be provided to ensure that you won't create a negative pressure in the toilet and make it difficult to open/close the toilet door. For smaller toilet exhaust cfm's, make up air can come through the undercut of the door (the distance between the bottom of the door and the finished floor). For larger amounts of air you need to have a transfer grill that would bring the required make up air from the adjacent room. For really big toilets you should think of providing some conditioned air. For example if you need an exhaust of 500 cfm, you may think of providing 300 cfm of conditioned air and transfer the rest from the adjacent room, using transfer grill.


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