# furnace fan



## eightball (Jun 16, 2013)

Im looking for plans to build a squirrel cage fan to use with a furnace. Any links or advice i would greatly appreciate.  Thanks, eightball


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## Dave Smith (Jun 16, 2013)

eightball   --squirrel cage fans are all over to be picked up cheap--are you just wanting to make one or do you have a special size you are  needing?   Dave


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## twstoerzinger (Jun 16, 2013)

eightball,
I am with Dave here - new and used blowers are readily available and not very expensive.
But, I also appreciate some one who wants to build something just for the journey.

You say it is for a furnace. Is this for a heating furnace - like perhaps a shop wood furnace or such?

If it is for a furnace in your house - buy a blower, you will have trouble getting a homemade machine quiet enough to let you sleep.

If noise and balance are not a concern, you could try welding one up.
The most difficult part will be getting the wheel balanced. Blower wheels are wide enough that they require a "dynamic" balance using a balancing machine. A simple "static" balance (like you can do in your shop) usually doesn't get you there. To add to complexity - the wheel also has to be "aerodynamically" balanced, meaning that each blade pulls with the same effort as the others - mostly a uniformity of blade sizing and positioning issue.

To design a blower wheel, you first need to determine the airflow and pressure that will be required.
The size and style of wheel are determined by the flow and pressure that it must deliver.
Basically, the diameter (and speed) determine the pressure that the wheel can deliver, and the width determines the volume (airflow) it can deliver.

There are 3 major styles of wheels - forward curved (or inclined) , radial, and reverse inclined. Then, there are dozens of modifications of each style.
For a home welding project, I would probably try a radial design - it is easier to set up. You can used aluminum or steel depending on your welding equipment.
Metal thickness would be about as thin as you can comfortably weld - perhaps in the 12 gauge range.

For heating systems, you usually size the airflow to limit the temperature of the heated air to about 180 deg F or so. For a first cut, the following equation gets you pretty close for heating air flow:

*CFM = 0.0083 * BTU/hr *(where CFM is cubic feet per minute of air) So if you had a 100,000 BTU/hr fire, you would use about 830 CFM of air.

If you are still interested, tell us what airflow and pressure you think  you need. I have worked with many blower designs over the years.
I can  help get you into trouble for sure.

Terry S.


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## eightball (Jun 16, 2013)

I really dont know what size i need yet. I am in the process of getting every thing together to build a home foundry. I think im gonna use an oil burner. I have one of those stanley squirrel cage fans (the plastic kind) that may work. But I really want this all to be made by hand. Ive never tried casting b4 but ive read alot about it and wanna try it. As far as balance is concerned, one of my duties at the paper mill is to balance rotors. We have a CSI machinery analizer that has a balance function. Excellent piece of equipment. We also have a roll balancer that i operate from time to time. I ground rolls for about 12 years and we static balanced all our grinding wheels.


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## Dave Smith (Jun 17, 2013)

eightball--I meant a metal squirell cage fan, but I have another sugestion. I have been to a couple of cast iron pours and they used a electric blower that was so loud that it got on everyones nerves, and even tripped a breaker from having a long small ext cord.....I was thinking that I would make a bellows that would be nice and quiet and belong in the time era of the old metal pours. --------:thinking: ---Dave


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## Metalmann (Jun 17, 2013)

Dave Smith said:


> eightball--I meant a metal squirell cage fan, but I have another sugestion. I have been to a couple of cast iron pours and they used a electric blower that was so loud that it got on everyones nerves, and even tripped a breaker from having a long small ext cord.....I was thinking that I would make a bellows that would be nice and quiet and belong in the time era of the old metal pours. --------:thinking: ---Dave






Like these?:


http://www.therebelpreppernetwork.com/how-to-make-a-bellows-for-your-homemade-forge/


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## Dave Smith (Jun 17, 2013)

Yes, it would work,  but I was thinking of a larger one on a base with a foot operated pedal    --Dave--








Metalmann said:


> Like these?:
> 
> 
> http://www.therebelpreppernetwork.com/how-to-make-a-bellows-for-your-homemade-forge/


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## eightball (Jun 17, 2013)

I am probably (once again) getting in over my head. Thanks for all the advice. Been around this trade long enough that one or two bad expieriences wont stop me. LOL  I know nothing about casting thats why i come and ask for advice.  Thanks all


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