Quote Originally Posted by dambo29 View Post
positive pressure system is better ... want to put an exhaust above and real close to the sink ...
The darkroom would have one large blower blowing into the darkroom and pressurizing it. The 'exhaust' above the sink doesn't need to have a fan - it is just a duct leading to outside of the darkroom. Since the pressure in the darkroom is higher the air flows out the duct carrying the 'fumes' out with it - I don't know why you would want to do that, though. "I love the smell of fixer in the morning".

If needed, a small 'assist' fan could be added to the exhaust duct, but it should not overpower the main blower that is pressurizing the darkroom.