# Make up air



## JBfromMN (Oct 19, 2010)

I am contimplating setting up my HF Dust collector with a pre-seperator and then venting it to the outside. My woodshop also doubles as a garage. It is heated by a vented natural gas heater.










My question is, I live in MN so starting to get a tad chilly around here. Does anyone at this latitude vent thier DC outside? If so, what do you do for make up air?


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## boboswin (May 23, 2007)

I'd have to say this is a bad idea.
Figure out the cubic feet in your workspace then divide the CFM of your dust collector into that an you can find out how long it takes to replace your room air with out side air.
At MN winter temperatures you are definitely going to be disappointed with that solution.


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## JBfromMN (Oct 19, 2010)

I kind of figured that myself, that is why I am checking to see if anyone else has done this.

I was just wondering what kind of performance I would get from not having to exhaust through any kind of filter.


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## Maggiepic (Aug 26, 2010)

If you create to much negative air pressure from venting your DC outside you can start drawing combustion gases (carbon monoxide) out of your ceiling heater. Unless you have a sealed combustion chamber that draws all the oxygen for combustion from outside, this can happen very easily. Essentially you would be reversing your venting on your heater. Any make-up air needs to be brought in from the exterior of the building and of course heated or cooled depending on the season. Most make-up air systems are roof-top style HVAC units but they can also be mounted at ground level on a pad of some sort then ducted into the building.

From looks of your pic, it seems you have a single wall pipe for your gas vent. If I am am wrong and you have a dual (pipe inside of a pipe) vent then you have a sealed combustion chamber. One pipe brings in combustion air and the other vent out gases. But like Bob said the unit needs to be big enough to replace the air you are pulling out with conditioned air.


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## Dcase (Jul 7, 2010)

Rather then venting it through your DC, have you thought about just mounting a furnace fan in a window or hole and just blowing it outside? Rather then just replacing the air in the shop you would just be blowing it. This shouldn't require a filter. I know there are codes against this in some cities though.


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## boboswin (May 23, 2007)

*Dan*, if you do this you would still need make up air to replace what your blowing out.

*GaryL* just explained that.


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## JBfromMN (Oct 19, 2010)

Yeah I understand the make up air thing, hence the title of the post. 

I was just thinking that the performance of the HF unit would be pretty descent if it did not have to push that air through a filter. I am going to get started on a seperator this weekend. If they weather does not turn too cold I will test vent it outside with the main door open. See what kind of performance I get. Then hook it back up to the filter and see if there is a noticable difference.


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## boboswin (May 23, 2007)

I guess it would have been helpful if you could have more accurately described which HF unit you were refering to.
There seems to be 4 or 5.

http://www.harborfreight.com/catalogsearch/result/?q=collector

If you already understand the principal of "make up air" then what purpose would your test serve?
There are several other considerations when you start removing the bag to decrease resisitance to air flow but you can google that. 
Try Bill Pentz site
I'm just curious because I originally took time to answer your query.


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## JBfromMN (Oct 19, 2010)

I was wondering how much air was needed is all and if anyone had done this before. Everyone seems to have the filter cartridge for them and I was thinking of just doing away with the filter all together for the increase in performance and to keep the shop cleaner.

To answer your question I have the later 2hp model with the 5 micron filter bag and lower plastic bag.

No one else seems to have done this here so that is the reason for my test. If the performance of the machine is not noticalbly better without the collection ring and filter attached then I will just get the filter and be done with it. I was just wondering if somewhere in the LJ universe there was someone that had set up this DC with it direct vented outside. If so what kind of performance increase did it yield. While I could use your formula laid out in your first post, the rated CFM of the DC would not be all that accurate without the filter bag attached now would it?

While I am sure there is some sort of engineering way to figure this out, I am more of an experimental person. I just thought I would ask here first.


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## brtech (May 26, 2010)

Of course to use the formula, you have to know the CFM of the DC, and the number on the carton is, uh, optimistic?

There is also the problem that you have to make sure that the makeup air isn't going to cause circulation of your exhaust air, with the dust, into the house/shop.


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## boboswin (May 23, 2007)

"While I am sure there is some sort of engineering way to figure this out, I am more of an experimental person. I just thought I would ask here first."

That's pretty much the answer I gave you at the outset but hey, tomorrow is Saturday go for it!


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## Maggiepic (Aug 26, 2010)

If your going to blow the DC outside with no filtration, or at least a quality cyclone separator, I hope there are no neighbors nearby. As Dan mentioned, your local zoning and building codes need to be addressed. If you get caught and/or turned in for blowing a combustible (yes sawdust) out to the exterior of your building, the EPA can also be involved. The fines could be scary. I would recommend at least some filtration, maybe a 30 micron.


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## JBfromMN (Oct 19, 2010)

I was thinking about piping the exhaust into a shallow hole in the ground. I live in a towm that has a working farm in it. Pretty small, so not going to upset the nieghbors. We get more dust from all of the fields and the gravel roads than from what little saw dust I generate.

If you look at the old Wood Whisperer videos, you will see he vented his outside at one time. Just posted here to see if anyone had any impressions on the performance of their dust collectors in this set up. I guess no one else has attempted this.


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## Knothead62 (Apr 17, 2010)

Word of caution- fine dust in the air around an open flame can cause a fire. A friend worked in a feed mill while in high school and learned to chew since the fine dust would flash/ignite like gas vapors.


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