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Old 08-12-2013, 12:31 PM   #1
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Trying to find cfm output capabilities for motor


I have this motor

I am trying to find a furnace motor and blower that will output 800 cfm at 1" w.g. and some. Can anyone tell me if this motor will work?
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Old 08-12-2013, 03:44 PM   #2
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Trying to find cfm output capabilities for motor


You would need to have a blower with the fan data for it. For anyone to tell you if it will do 800 CFM at 1" plus static.

But I would guess not. If your talking about a standard 3 ton drive furnace blower.
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Old 08-12-2013, 07:20 PM   #3
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Trying to find cfm output capabilities for motor


My actual need is 600 cfm at .77 " w.g. I was overdoing it and likely doing my math wrong. I have a 24x36" hepa filter which can be found here http://www.filtera-b2b.com/businessf...re09072004.pdf
it is the 99.99% model. I need it to blow between 100-150 fpm out the front of the filter. I'm pretty sure my math is close or in the ballpark and i need to go a little extra to makeup for the filter getting dirty over time and having a larger resistance.

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Old 08-12-2013, 07:30 PM   #4
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Trying to find cfm output capabilities for motor


A standard furnace blower will get you your 200 CFM. At statics well above 1".
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Old 08-13-2013, 07:38 AM   #5
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Trying to find cfm output capabilities for motor


You are attacking the problem from the wrong end. Motors don't have cfm ratings, blowers do. You need to select the blower first.

http://www.grainger.com/Grainger/ecatalog/N-1z0dq0q
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Old 08-13-2013, 10:56 AM   #6
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Trying to find cfm output capabilities for motor


Any ideas what to look for when looking for a used one? Your saying its the fan and the housing then? Every one I have looked at only has a model number on the motor and never on the housing. I'm thinking its just going to have to be a guessing game but In your opinion would most 1/2 hp's have what I am looking for?
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Old 08-13-2013, 11:57 AM   #7
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Trying to find cfm output capabilities for motor


what R U using this for? a furnace or other project? fans are part of a PACKAGE with ductwork and that is how the CFM and flow is rated for and measured against. the more restrictive and smaller the ductwork the higher the static pressure it works against and the flow drops. not as simple as getting a few model #s.
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Old 08-13-2013, 04:04 PM   #8
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Get a Grainger catalog. look in the fans section. You will be able to find the blower you need.
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Old 08-14-2013, 12:01 AM   #9
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I could definitely find the blower I need on grainger but due to money restrictions thats not possible at this time. I have a project called a "flow hood" Here is a link to an example:
http://www.canadianfungi.ca/hood.php

I have a 24x36" filter 6" deep and 99.99% effeciency with the specs here:
http://www.filtera-b2b.com/businessf...re09072004.pdf

It says the filter at 175 fpm has 1" w.g. I need it to flow at 100 fpm so I did some math since it appears to be mostly linear on the graph and got that at 100 fpm I will have .5714" w.g.
Now This will also have a standard prefilter which is in general avg. out to .2"w.g. so all together I should need roughly 600 cfm (2ftx3ftx100fpm) at .77" w.g.
Now to be sure anything more than 600 cfm can easily be restricted as shown in the posted example. And I'd rather it be over.
So all this being said can anyone with good hvac experience tell me if a standard 1/3 hp motor with say an 8" wide fan blades give me the power I need? I'm guessing with all the restriction the guy had to put on his to get his down to 100fpm leaving the filter. Any advice is welcome but please only people with some experience with these blowers. Thank you again in advance for any time taken to help me.
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Old 08-14-2013, 05:13 AM   #10
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Trying to find cfm output capabilities for motor


I think you have something turned around.

A filter that has 1050 CFM of air moving through it 175 FPM, at a static/resistance of .5", Will only have .16" static/resistance at 600 CFM(100 FPM).

You need to know the actual static/resistance you will have/be working against, to be able to calc blower size and horse power. Or, you will end up doing a lot of trail and error testing.

PS: The FPM to CFM conversion doesn't work out exactly on air filters. Since it is not a true free area opening. As the media takes up some of the area.

I generally don't work on blowers that move more then 70,000 CFM, or less then 200CFM.

Use the Grainger catalog to find out what blower wheel size you need(or what CFM the one you have is, at what RPM. Then horse power can be calculated from there.
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Old 08-14-2013, 08:37 AM   #11
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Trying to find cfm output capabilities for motor


and to add to the equation direct drive blowers don't like restrictions added to the intake or they can wobble like crazy or cavitate. belt drives are very tough and can tolerate what he did better. direct drives are meant to work against some closed ductwork and not run in free air. has to do with the type of fan blades and design. those old belt drives should be easy to get from most furnace installers or scrap yards
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Old 08-14-2013, 10:43 AM   #12
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Trying to find cfm output capabilities for motor


Been there, at 175 fpm the resistance is 1". I figured it down to .77 from the drop to 100 fpm. Not sure if that changes any of the advice given.
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Old 08-14-2013, 05:21 PM   #13
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Trying to find cfm output capabilities for motor


Sorry, did the calc on the wrong filter.

Doing the calc on the 24X36X6 99.99% filter(1" static at 175FPM). FPM slowed to 100, brings its static(resistance to air flow) down to .3249".

The pre filter, if it has a .2" static at 175 FPM, will only have a static of .0649" at 100 FPM.

So your total static of the filters would only be .3898". Doesn't take much of a fan to move air through that low of a resistance.
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Old 08-14-2013, 05:51 PM   #14
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Trying to find cfm output capabilities for motor


The below link, is just for you to be able to see the size motor and blower you would want for this set up. The motor is much smaller then you thought you needed.

http://www.grainger.com/Grainger/DAY...&cm_vc=IDPRRZ1
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