spray booth design: Static pressure of a furnace filter

HawkeyeHobbies wrote:

The one factor most forget is that a fan does a better job of sucking air than it does of blowing it when ducted as we do for paint booth setups.

Hi, Gerald.

Fans actually push more efficiently than they pull, by a factor of almost 10 to 1, depending on the fan type and setup.

The fans in bathrooms are actually little more than "helper" fans, IMHO.  They are primarily responsible for removing heated water vapor.  Since heat rises and water vapor is lighter than air, it doesn't take a lot of "pull" to move that up and out.  I would suspect that one of the primary reasons fans are being moved higher up is to reduce the amount of noise.  The fan in my bathroom is incredibly noisy.  I hesitate to turn it on in the early mornings because it interferes with my wife's ability to sleep.

Exhaust fans for spray applications are a different animal.  In this case you're tasked with removing room temperature heavier-than-air vapors.  You first have to capture them (hence the 100fpm face recommendation), then move them through x amount of duct work, and then out of the building.  Bathroom fans are great for what they are designed to do, but that purpose is also one of the primary reasons I don't recommend them for use in a spray booth.

Gip

Way too much technology for those building a simple air movement device that is used infrequently.

True the better quality the filter the great air resistance it places on the fan moving the air down the duct work. The purpose of the filter is to collect the larger particulates to prevent them from clogging the duct work and fan blade surfaces. Personally I think the 3M premium filters are too much. Most of the fans we use for paint booths don't have the CFM under load rating to handle them. And if you were to use such a fan, you'd better be holding that airbrush close to the model when spraying as well as a firm grip on the model as well.

In my set now I don't use a filter, I just give the fan a good scouring as needed to remove the debris built up on the blades. Takes just a few minute to do. 

The one factor most forget is that a fan does a better job of sucking air than it does of blowing it when ducted as we do for paint booth setups. The best place for a fan is at the exhaust end of the system...closest to where it vents outside. Even on higher efficiency homes with good bathroom exhaust systems, they are now placing the fan unit closest to the exit end of the system. This gives one a quieter and greater flow of air than a ceiling mounted unit with several feet of ducting between it and the exit point.

I'm going to be redoing my paint booth exhaust system in the next few weeks, and will also start replacing those noisy inefficient bath fans as well.