Creating circular airflow in small converted shed

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Forum topic by Ian S posted 08-25-2016 05:57 PM 1005 views 0 times favorited 11 replies Add to Favorites Watch
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Ian S

33 posts in 1181 days

08-25-2016 05:57 PM

Hey folks,
For those who remember my earlier posts, in the last 6 weeks the wife and I have been insulating, rewiring, and finally closing in our back yard shed, to turn it into a proper workshop! We have finished putting up interior walls, so now it’s just a matter of the “fun” stuff—creating homes for appliances, putting up lighting, fans, and so on.

What I’m trying to do now is create good airflow and circulation in the small space. Here are the details:
  1. The shed is roughly 10’ x 20’—long walls are oriented N/S, short walls are E/W.
  2. We have a thru-the-wall A/C installed on the east wall, about 2/3 of the way toward the north end. This may not be optimal, but it would be a pain in the butt to move it.
  3. We have a WEN 3-speed air cleaner (the cheapest “decent” one from Amazon) that we plan to mount somewhere just below ceiling level. The ceilings are low, only about 7 feet, so there’s not a lot of space to get this much lower.
  4. We will have at LEAST one wall-mounted fan, probably in a corner somewhere.
  5. The GOAL is to both circulate the cooled air from the A/C, AND circulate dust in the air so that it gets through the air cleaner.

Most importantly: refer to this drawing to see how I propose to set things up

As you can see I’m aspiring for to create a counterclockwise air flow. I’m only doing it this way because I think it’s probably the best way to take advantage of the cooled air from the A/C. Also note, probably the majority of our cutting and dust-making is going to be near the center of the room. So when dust is created, it should be blown south, and hopefully circulate into the air cleaner before coming back to the north end.

  • Does this setup make sense?
  • Is there a better way to create the circulation I’m going for?

That should do it for now. Thanks for your thoughts as always!

11 replies so far

View Cooler's profile


299 posts in 1327 days

#1 posted 08-25-2016 06:42 PM

In my old apartment I bought four (4) Honeywell small fans:

These fans have keyholes on the bottom of the base that allow wall mounting.

I mounted one fan in each corner of the room angled just a few degrees toward the center of the room. I set all the fans so that they created a circular air flow in the room. Having the four mounted high and aimed slightly to the center of the room and slightly down caused a turbine effect that was more comfortable than the large circulating fan I had previously. They also consumed no floor space.

I see that there are two models available. And one is much more expensive than the other. My main room was about 15’ x 25’ and the fans I bought from Sam’s Club came two per carton and cost about $30.00 for the pair. When I get home tonight I will see if there is a part number on them.

I also made an “air cleaner” by bungeeing onto a box fan one of those furnace filters. The filter gets dirty so I know it is working to some degree. About $30.00 total. I should build a box for this. If I do I will use a $3.00 fiberglass pre-filter over the more expensive 3M filters. I think it will allow the 3M filter to last longer. Very little flow is lost with the cheap fiberglass filters (but they only filter out big pieces of dust).

-- This post is a hand-crafted natural product. Slight variations in spelling and grammar should not be viewed as flaws or defects, but rather as an integral characteristic of the creative process.

View Dustin's profile


695 posts in 1224 days

#2 posted 08-26-2016 12:22 PM

If you’re planning on working in that enclosed space, it seems like you’ll end up with a lot of dust collecting on the south side of the building (at least, anything that doesn’t stay airborne long enough to recirculate). Are you planning on using any kind of dust collection besides the WEN filter? If not, I’d strongly recommend the use of a good respirator. It seems like your proposed set up would clean the air adequately if run for a while after work was done, but you’ll still be exposed to a lot of it while working.

-- "Ladies, if your husband says he'll get to it, he'll get to it. No need to remind him about it every 6 months."

View Cooler's profile


299 posts in 1327 days

#3 posted 08-26-2016 12:50 PM

My oil delivery company said that they would cancel my service contract if I didn’t do something to control the amount of dust in the basement. Apparently they were blaming the dust for recent services.

I don’t know if it solved the furnace problem but dust collection makes things much cleaner in my basement. I recommend it.

-- This post is a hand-crafted natural product. Slight variations in spelling and grammar should not be viewed as flaws or defects, but rather as an integral characteristic of the creative process.

View Ian S's profile

Ian S

33 posts in 1181 days

#4 posted 08-26-2016 01:08 PM

Thanks for the tips so far guys.

For the short term I will definitely be wearing a respirator while using anything that produces much dust. We are also using a fairly powerful shop vac to try to hack together a simple dust collection system. It’s not a proper dust collector so I know we’re not going to have optimal CFM or whatever … but for the short term I would think it’s only going to help and not hurt us. We’re referring to this video for inspiration.

View Cooler's profile


299 posts in 1327 days

#5 posted 08-26-2016 01:37 PM

I watched the video. The guy works very fast. It would take me much longer to do this.

-- This post is a hand-crafted natural product. Slight variations in spelling and grammar should not be viewed as flaws or defects, but rather as an integral characteristic of the creative process.

View Bob5103's profile


142 posts in 1317 days

#6 posted 08-26-2016 03:05 PM

My shop is narrow, I mounted my air filter on its side. It is centered in the shop and does a good job filtering and circulating the air. And it was much easier to do than suspending it from the ceiling.

View JBrow's profile


1368 posts in 1404 days

#7 posted 08-26-2016 03:46 PM

Ian S,

While circulating and cleaning shop air is a good idea; keeping as much dust out of the air when generating dust is even better. Therefore, a good dust collector with as much suction as can be afforded in the budget and connected to the various machines would reduce the volume of dust in the air and the air cleaner would not have to work as hard.

I am not an HVAC or air flow engineer, so I may be wrong, but I suspect the results from you current plan will be disappointing. The biggest problem from my vantage point is the size and shape of the shed versus the limited capability of your equipment. But if you go ahead and install the equipment as you plan, you may find it works just fine. If not, then relocating the equipment could achieve better results. My thoughts on improving circulation over your current design are…

As I understand air flow, the force driving air movement diminishes as the square of the distance from the fan. As a result, air movement 10 feet away from a fan will result in a 100 fold decrease in the force driving air movement. Additionally, since air flow from a round fan follows the outline of a cone, where the tip of the cone is centered on the fan, the air flow becomes increasingly spread out in all directions as air gets further away from the fan.

The shape of the shed can also impact air flow. The rectangular corner will probably interrupt flowing air and create turbulence as the air is forced to change direction. This turbulence can also reduce air flow and allow particles to settle out of the air. If the shed corners were rounded, air flow could smoothly transition from one direction to another; but rounding corners not very practical.

Recognizing the issues associated with establishing good shed circulation is the easy part; figuring out the solution is, at least for me, more difficult. If you are locked into the plan drawn, I would think a pair of fans mounted on west wall would be needed to boost and direct air flow. If the added south end fan is angled, maybe that could reduce some of the turbulence that would otherwise occur in the southwest corner. Then moving the air cleaner closer to the A/C and adding another fan in the southeast corner, also angled could help air make the south east corner direction change.

In this configuration, I think air flow will be stronger and allow larger dust particles to remain suspended in the air for air cleaner scrubbing. However there will likely be dead spot in either your proposed design or the revised design suggested. One such dead spot is the northwest corner; another is the center of the shed.

An alternative to attempting to achieve a circular flow of air is to move the air in a linear fashion. The air cleaner could be mounted on the west wall mounted toward one end or the other of the shop. On the east wall a series of fans mounted to move air from east to west would force air across the shop. Then one or more fans mount on the west wall could capture air from across the shop and direct it toward the air cleaner intake.

If you have access to the attic of the shed, then perhaps running for HVAC flexible dust work could result in ceiling or wall vents and with a distribution of air intakes and outtakes. The duct work home run to a center location powered by an HVAC re-purposed squire cage fan could draw air into the ducts through the squirrel cage fan and then returned to the shed. The air cleaner, mounted either centrally in the shed or near the biggest dust producing machine would clean the air of particles not captured by the filter in-line with the squirrel cage fan.

I have found that some local HVAC contractors are willing to give away squirrel cage fans from equipment removed when a homeowner replaces their furnace. I have found these re-purposed fans are quite, move a lot of air, and are reliable.

View clin's profile


1057 posts in 1480 days

#8 posted 08-26-2016 04:15 PM

Due to momentum, the air blowing out of a fan will have much more speed than air getting sucked in. This is one reason to mount an air filter nearer one end of a room and have the intake on the short end. Similar to your proposed location for your cleaner. Though another line of thinking is to have the air filter intake located as near the dust producing equipment (table saw?) as possible.

I would move the fan to the west side near the northern end and have it blow due south. Its air will blow south, into the SW corner. It will have to turn towards the east, be drawn into the air cleaner and get blown north. Forced to turn west, towards the fan. Round and round it goes.

It’s not that large a space and with a cleaner, fan, and AC unit, air will be moving around pretty good. However, there will always be dead spots and while the air filter will help a lot to keep the air clean, you’ll still get dust settling around the shop.

The dust around the shop is an issue even when you are not making dust. Just moving around the shop will kick dust up. And FYI, based on my particle counter by an order of magnitude, sanding operations are the worst for creating dust.

As for the AC getting circulated, that’s a non-issue. The very cold air out of the unit wants to fall down and will spread out throughout the shop. Though of course a breeze always makes things feel cooler, so the fan is good and the air filter just more.

-- Clin

View Ian S's profile

Ian S

33 posts in 1181 days

#9 posted 08-26-2016 06:18 PM

Thanks JBrow and Clin. That’s real good stuff right there. I think that’s the feedback I was looking for.

View MT_Stringer's profile


3183 posts in 3715 days

#10 posted 08-27-2016 01:52 AM

A Dust Deputy hooked up to your shop vac will collect a lot of the dust from your tools. And your Shop Vac will love you too. It won’t get dirty or fouled. Almost every bit of dust will be collected in the bucket.

I have one that I hook up to the miter saw, Random Orbital Sander and the router table. I had forgot about it until this week. I checked the bucket and it was full, completely full! The rest was carrying over to the shop vac bag. But the filter was still clean.

The pictures are hard to decipher but I have pvc pipe manifold that connects the shop vac (via Dust Deputy) to the miter saw, belt sander, and a port for hooking up a hose for other tools like the ROS or Kreg pocket hole jig or general clean up.

Hope this helps.

-- Handcrafted by Mike Henderson - Channelview, Texas

View clin's profile


1057 posts in 1480 days

#11 posted 08-27-2016 02:20 AM

+1 on using a Dust Deputy with the shop vac. I use a bag in my vac and it never gets much in it. but between the Dust Deputy and bag, it allows me to use a HEPA filter in the shop vac. That filter just never gets much of anything on it. The exhaust from the shop vac is pretty clean. So the thing doesn’t act like a dust pump.

Life gets way easier, with a shop vac, if you get a long hose for it (I uses a 20 footer). Shop vac can stay in one place that way. Large hose is bulky, but beats the heck out of dragging the vac around the shop.

Of course putting in vac lines is always an option too.

-- Clin

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