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Exhaust Requirements


I much enjoy reading and following the posts. I hope to someday be able
to put many of the tips to use. As for now I make my living doing
commercial HVACR (Heating, Ventilating, Air Conditioning, and

Please consider that with every Exhaust of air that air needs to be
replaced, otherwise, a “negative” is established that tends to hold in
contaiminents. That replacement air is referred to as Makeup Air.
Requirements for MakeUpAir (MUA)vary depending on:

How tightly sealed the bluiding/area is
Any combustion (Gas Furnaces etc. (consume Oxygen))
any exhaust (bathroom fans, kitchen vents, clothes driers, etc
Chiminey effect (Hot air rises out a “chimeny”)

A good rule of thumb would be to provide a larger size inlet where the
air moves past you towards the exhaust fan. This has the benefits of
moving the fumes away from you and providing for a good level of Fresh
MUA and helping to keep a healthy level of Oxygen in the air.

The air flow pattern can be tested through the use of smoke, candle
flame etc.

Hope this gives you all a good starting point for a healthy workbench

Dan in the Midwest Sauna,


While I do not do the engineering/design on systems, I do know that
there are tables listing recommended number of air changes per hour
based on usage and occupancy. Then the volume of the room is
calculated; multiple by number of air changes per hour; divide by 60
minutes per hour and that should give you Cubic Feet per Minute.
((Volume in Cubic ft x ACH) / 60 3DCFM) You may be able to find
ASHRAE tables to determine your Air Changes number at the library.

Remember that the air you exhaust has to be replaced from somewhere
to avoid an unhealthy environment. (Room being in a negative
pressure, can concentrate pollutants etc.)


PS I do HVAC work as my main job