# Differences is CFM?



## drp (Mar 6, 2020)

I am still looking at small single stage DCs and have a question. I don't understand the difference in CFM rating on 1HP units from the same manufacturers. For instance, a 1HP wall mounted unit is rated at 537 CFM and the same manufacturer has a 1HP portable unit that is rated at 800CFM. Does this seem right? I understand they are in a different configuration so they won't be identical, but I would think that the CFM ratings would be closer to the same. Any clarification on this would be greatly appreciated.


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## FrankC (Aug 24, 2012)

The CFM is determined by the design of the impeller unit, not the HP of the motor, different units, different CFM.


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## _Ogre (Feb 1, 2013)

a desk fan will move 500 cfm and barely move the paper on the desk
what units are you looking at? cfm on dc systems is like hp ratings on shop vacs
the wall mount 1hp grizzly at amazon says "Air suction capacity: 450 CFM; Maximum static pressure: 7.2"
the big single stage 1hp grizzly has this "Air suction capacity: 640 CFM with elbow, 800 CFM without elbow, Static pressure: 3.3"
maximum static vs static? a lot of smoke and mirrors
the biggest difference is the wall mount has a 30 micron filter, the biggest 1hp has a 1 micron filter
1 micron will have a lot less dust in your shop air


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## woodnthings (Jan 24, 2009)

A dust collector is a blower which displaces a volume of air, creating "suction" at the inlet end and forces that air through a filter, a bag or a cannister. The finer the filter, the less dust will enter into your shop air passing through the filter, BUT the more difficulty the air will encounter trying to push through the filter, especially as it gets clogged with more dust. SO, you gotta shake the bag once in a while or rotate the paddle on the cannister to make the dust drop down into the collection bag or barrel.
Boll Pentz has a great site to learn all there is about pipe size, HP, blower size, air flow, etc:





Dust Collection Research - Dust Collection Basics


This site helps small shop workers understand the risks from fine dust exposure and how to effectively protect themselves and their families from airborne dust hazards. Fine dust is so extensively studied that researchers call it PM short for particle material. A Google search on PM Health Risks...



billpentz.com


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## drp (Mar 6, 2020)

_Ogre said:


> a desk fan will move 500 cfm and barely move the paper on the desk
> what units are you looking at? cfm on dc systems is like hp ratings on shop vacs
> the wall mount 1hp grizzly at amazon says "Air suction capacity: 450 CFM; Maximum static pressure: 7.2"
> the big single stage 1hp grizzly has this "Air suction capacity: 640 CFM with elbow, 800 CFM without elbow, Static pressure: 3.3"
> ...


Very confusing to my simple mind. I was looking at the Rikon, Power Tech and Shop Fox units. I like the idea of the wall mount units to save space and then run the hose from machine to machine. Price wise they are all pretty similar. I believe they all have a 2.5 micron bag. I also considered the 1 hp HF unit, but would need to replace the bag since it comes with a 30 micron bag.


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## woodnthings (Jan 24, 2009)

Too much flex hose will hurt your air flow. Read the Pentz site about flex hose. My flex hose is no more than 5 ft long and my dust collector(s) are on casters so I can move them right to the machine I'm using. It take only a few second to attach the hose to the quick connect fittings I put together from PVC and a Rockler fitting.

From the Pentz site on ducting and resistance:





Dust Collection Research - Ducting


This site helps small shop workers understand the risks from fine dust exposure and how to effectively protect themselves and their families from airborne dust hazards. Fine dust is so extensively studied that researchers call it PM short for particle material. A Google search on PM Health Risks...



billpentz.com




_One common mistake is to use standard flex hose as most of this hose is poorly made with ribs sticking into the airflow adding up to nine times the resistance of smooth pipe. Always buy and use a minimum of smooth interior walled flex hose as it that only adds about three times the resistance of smooth pipe. _


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## epicfail48 (Mar 27, 2014)

As frank already mentioned, the HP rating of the motor has almost no bearing on the CFM rating of the unit. A certain sized motor will have a limit on the size of impeller it can physically spin, but not all manufacturers are going to be building to that limit

CFM is also only one spec that matters on a suction device, equally important is suction power, usually given in static pressure. A high CFM unit with low pressure abilities is a lot less useful than a medium CFM, medium pressure unit. A dust collector has to have some suction force to it, not just move a lot of air


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