Exhaust Fan Questions

[Shawn F.]

I am looking to put a new exhaust fan in my 3000 sq ft shop but have a few questions before going out and buying one this week. I do not want to spend much more than $300-$350 on one if at all possible. Right now I have the biggest fan that Lowes sells on wheels that is blowing towards the outside of the bay door but towards the back of the shop there are no windows, doors, etc to get a draft going though. Up high in the back far corner is a boarded up fan vent/hole where there used to be an exhaust fan with the wires still hanging. I would like to put a new fan there and wire it up and set the 2 other fans I have at the bay door for a draft.
My question is what CFM exhaust fan would I need to move some air across a 3000 sq ft building? I am looking at fans from Northern Tool by the way...

Thanks a lot for any info, suggestions or comments!

 

[nti06]

Consider a reversible fan whichever way you go. On a cool night with the garage door raised about 6 inches you get a good incoming draft.
On a day when you seafoam an engine or accidentally pour oil on a hot manifold, you could flip a switch, reverse the fan, and blow the smoke/fumes out the door vs. pulling it all through the shop.

 

[Shawn F.]

Thanks for the advice... Now do they call them reversible fans or something else? It looks like Northern Tool doesn't carry any of these locally and I will have to ship it in.

 

[Falcon67]

I think you'll need something the size of a 36" whole house fan to move air in a space that size.

 

[pseudorealityx]

Without a path for air to come from one side and exit the other, you're not going to get a good draft.

A big attic fan blowing out the roof wouldn't hurt, but I haven't priced them out.

 

[6768rogues]

You can calculate the air volume of your building, then by using the fan CFM you can figure how many air changes will occur per hour. Then it is important to have unrestricted makeup air and to configure the fan and makeup air openings so that the air is mixed as it changes and not short-circuiting from the makeup opening to the fan.

 

[wb2vsj]

Don't know where you are in NC, but near Raleigh there is a AgriSupply and they carry exhaust fans. Just FYI. Check for any other Farm Supply stores near you.

Walt

 

[Charles (in GA)]

Don't know where you are in NC, but near Raleigh there is a AgriSupply and they carry exhaust fans. Just FYI. Check for any other Farm Supply stores near you.

Walt

Think "chicken houses".

http://www.nextag.com/poultry-house-fans/shop-html

Charles

 

[nwav8tor]

Thanks for the advice... Now do they call them reversible fans or something else? It looks like Northern Tool doesn't carry any of these locally and I will have to ship it in.

Not sure if this would work, but I think you sould be able to wire up a "regular" fan using two switches that would reverse the polarity of the current to the fan motor depending on which switch was turned on. Then the fan could be operated either as a cooling blower or exhaust fan. Just make sure there is an interlock of some sorts so both switches can't be on at the same time and short out the whole system! Rather than using 2 switches, I'm pretty sure you could find some sort of 3 position (Fwd - Off - Rev) switch available that would do the same thing providing a foolproof built-in safety interlock.

Paul

 

[Random Guy]

Um... That isn't how AC motors work. The curve of the blades would also be wrong when you are running the fan backwards.

 

[Gary S]

What are you trying to accomplish? If you are planning on cooling the shop using North Carolina heat and humidity, good luck.
Insulate well, and add a bit of air conditioning, and you get rid of both the heat and the humidity.

 

[BadgerBoilerMN]

What goes out, must come in or you will be pulling a negative. Reversible...I don't think so. In hour climate, warm air will be at the ceiling and most of what you generate in the shop will go with it. Any fan should be near the ceiling and open a screened door on the opposite side of the building for ventilation.

For general fresh air an Energy Recovery ventilator is the thing. Mini-splits cool my radiant heated shops.

If you have equipment to vent e.g. welders, grinders, paint booths, the manufacturer will have the spec.