Putting together an exhaust fan

[bad_idea]

I have this fan setup and want to use it for an exhaust fan in my garage. My garage is 14x20. I want to mount a filter housing for a home furnace in the ceiling with the fan pulling air through it out a vent in the exterior wall of the garage. I do a fair amount of welding in the garage and want to vent the fumes outside. The grinding dust also makes a mess and figure the filter should trap a good amount of that. My issue is I don't know what kind of housing to build for the fan. I am also not sure how much air the fan moves. I do know the fan pulls air through the round hole in the fan blade and throws it out the sides. Guesses at CFM of fan? Maybe some pics of a housing to copy? I intend on building the housing out of wood and duct-work readily available at home depot. Cheap being the priority. Thanks for any info. Disregard the compressor tank the fan assembly is c-clamped to and the mess all over the work bench.

 

[BDT/NWMN]

I am going to do the same thing with a furnace blower and ample ductwork.... My blower is way more """complete""" than what you picture ..... I would find a more complete blower.. waaaaay easier..

 

[danielzig]

I believe the housing the fan was situated in has a lot to do with the air flow that you will experience. The housing is designed for the fan to be able to move air out in a certain motion.

 

[HOTFR8]

Bad Idea you have just given me a great idea to make a pit exhaust fan. That would also work well for a paint booth.

 

[bad_idea]

Considering this fan was free, I would like to use it. I have been looking for a while now and have not been able to find anything cheap. Building a housing is half of the fun. I plan on following this through unless the fan isn't going to pull enough air. Anyone have an idea of how much air this thing should move?

 

[HOTFR8]

How mush air it moves will depend on how fast that motor spins the fan.

 

[pseudorealityx]

What size furnace did it come out of?

The "box" containing a centrifugal fan actually doesn't do a lot for airflow. These fans work by pressurizing the box, and the air goes whichever way the pressure decreases.

 

[danielzig]

The design of the fan chamber does do something for airflow on certain types of fans. Depends on the design. If this came from an inline fan I would say you are correct but if it came from a fan that had a side inlet and 90 degree discharge, it does matter. To what extent, I am not sure.

What size furnace did it come out of?

The "box" containing a centrifugal fan actually doesn't do a lot for airflow. These fans work by pressurizing the box, and the air goes whichever way the pressure decreases.

 

[bad_idea]

I received it exactly as you all see it. I have no idea what it came out of. My next question is can it be mounted with the fan blade pointed down? Is that how is it meant to be mounted? Otherwise I will have to have a 90 going down to the filter. I think the difference between mounted horizontally (as shown in the pictures) and vertically is the bearings in the motor. Would the bearings be different for the shaft also? I have very basic knowledge of bearing design that I learned in apprentice classes.

 

[bad_idea]

What size furnace did it come out of?

The "box" containing a centrifugal fan actually doesn't do a lot for airflow. These fans work by pressurizing the box, and the air goes whichever way the pressure decreases.

Are you saying I could build a square box? That would definitely be easier to build. I was thinking I would have to make something round. Again, I have no idea what this assembly came out of. I received it exactly as shown in the pictures. Thanks again.

 

[HOTFR8]

A square box would work well, all you need is an inlet and an outlet for the air you want to move.

 

[pseudorealityx]

The design of the fan chamber does do something for airflow on certain types of fans. Depends on the design. If this came from an inline fan I would say you are correct but if it came from a fan that had a side inlet and 90 degree discharge, it does matter. To what extent, I am not sure.

Does it do 'something'? Sure.

For the OP's attitude of 'this is what I've got, this is what I'm using'... Meh, not really.

To get the most out of it, you would want a nice big radius into the inlet. The outlet isn't going to do a lot unless you really make some nasty transitions.

As far as inline fans... depends on what kind. Inline axial, inline mixed flow, or inline centrifugal. This is a straight centrifugal though, so it's pretty cut and dry.

 

[Alchymist]

That type of fan usually uses a round housing with a radial outlet coming off at a tangent to the fan. There is an optimum size rectangular opening in the wall of the circular housing for maximum airflow. I'd build a circular "tube" to fit the fan ends (think round cheese box), with a hole in one end to match the inlet, and start with a rectangular opening in the round wall about 3" wide across the width of the fan. Make a transition duct about a foot long, and check airflow. Keep increasing opening until max airflow.

 

[bad_idea]

I don't mean to be dense, but I am not following you Alchymist. Could you please dumb it down for me? Thanks.

 

[Alchymist]

Here's a really quick and crude dwg:

 

[Alchymist]

Better yet:

 

[bad_idea]

Alchymist you are the man! I thought it was something like that. Making that ought to be a fun project.

Now if I can mount the fan in the vertical position (if the current view is horizontal) that will keep me from having to make a 90 degree elbow for the intake. Anyone know how to determine the bearing type?

 

[pseudorealityx]

Here's another photo with a filter box attachment. This one has a MUCH simpler outlet.

I wouldn't be on it being happy being vertical. You need to look for a thrust bearing of some sort. I'm not familiar enough with design to point you to an exact identification. I'd just build the elbow and be safe.

 

[Full Throttle]

google centrifugal fan, air comes in the center and out through the edges, you must have a valute. That wheel in a square box will have the same effect as a screen door in a submarine.

the pic above does not show the valute on the return (negative pressure) side of the fan, gotta have it.

 

[pseudorealityx]

google centrifugal fan, air comes in the center and out through the edges, you must have a valute. That wheel in a square box will have the same effect as a screen door in a submarine.

the pic above does not show the valute on the return (negative pressure) side of the fan, gotta have it.

The inlet side is important to match the inner diameter of the wheel. The outlet is NOT that important.

http://www.greenheck.com/media/pdf/catalogs/SQBSQ_catalog.pdf

Lots of images and photos of small commercial fans.