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Safety -- Make sure you are safe!

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Old 2015-08-23, 4:37pm
JimW JimW is offline
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Join Date: Jul 14, 2014
Posts: 20
Default Garage ventilation using funnels

On to ventilation:
We use 2/3 of our 3 car garage for glass & jewelry and after settling on where to put things I revamped the old cross breeze ventilation.
I read everything, all the new and old threads and have seen plenty of vent hoods in biological and chemical labs where I do calibrations. I've even had experience with mapping the flow.
At the end of the day, I opted for funnels to keep things more open.

1 big problem to overcome is the layout:
No window, we have a back door and the 2 garage doors, bedroom above the garage and wall-wall, floor to ceiling cabinets on the side walls.
This pretty much required me to make a semi-portable system that me or the Mrs could put together quickly and easily plus be able to stow away neatly.

Vent size: I experimented with 4, 6 and 8 inch vent. 4 is worthless, 6 and 8 are very close as far as CFM, mainly limited by the size of the fan, but for a funnel I want increased velocity going into the opening, as well as adequate volume, so I went with 6 inch.

Fan: I know that radial fans are best for moving gas. I also needed to pull air thru 2 funnel openings and I had to decide on one big blower or 2 smaller ones.
I decided on a sawdust extractor from harbor freight to get the blower out of, plus I got a bunch of other re-purpose-able hardware.

It claimed to have 1550 CFM which is more than double any other single 6 inch, and lots of 8 inch, axial blowers I could find.
The inlet is a tad over 5 inch, so I used a 5-6 inch adapter and a clamp to get it to 6 in.
I mounted it on a small dolly but sat it on another one to lower the inlet..this is temporary and the duster can is for scale.

Basic construction: I cut a hole in an old folding table and ran the duct down thru it, using 1 90 deg bend to turn and go straight back to a place to connect a 5 foot section with a 90 deg bend that connects to another 5 foot section that goes to the fan inlet. This puts the blower further away to hold down noise. The outlet runs down a long hose that gets shoved under a little trailer parked there.
The top of the duct turns with a 90 deg, then to a “Y” where I used flex duct and 6 to 8 inch adapters for the funnel inlet. The funnel inlet is 10 inches from the torch tip.
I used screws anywhere there was stress on the connection.
My thinking was that with the air column falling down and out, rather than up and out, it would reduce the pressure and pull more air.

For our surface we've always used 2x3 granite slabs we got at Home Depot with bent-just-right aluminum door flashing around the back and sides to stop the random glass skittles.

Here's pics of the whole thing:

I used an Omega airflow meter to get velocity and CFM measurements.
Velocity is directly measured ( I looked for a sustained peak)
CFM is taken over a 60 second average all over the vent opening, which is set in the instrument to 8in dia. before the measurement.
For measuring the CFM and velocity away from the inlet, I used an imaginary 8 inch diameter “tube” coming straight out of the 8 inch funnel opening, extending to the torch tip.
I work well within an 8 inch diameter area around the flame and was interested in my actual work area.
Here's the results:

The pull of the funnel changes the flame.
It tightens it a little bit if it's a strong flame, but a soft flame is slightly bushier. We both use Alpha's.
The extra air blowing over your work seems to cause striking glass to strike quicker and changes how reduction glass changes colors.
It's cooler at the end of the flame.
The intake noise makes talking to each other hard but headphones are nice too.
I set closest to the garage door and can't really hear the fan over the intake noise.
I added a good remote switch, to turn the blower on and off from the bench.
Plenty of real life suction. It can easily pull a big “yellow” flame in and can slightly “bend” a reduction flame.
When I was testing with incense, our son came out to look and mentioned you smell it outside but not in the garage.
We both feel slight air movement over our shoulders.
The funnel and all connections stay cold. The flame stops about 3-5 inches from the opening, depending on what I'm doing.
If you needed to move your torch up or down very much, the flex vent is adjustable.

Good Luck!
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Old 2015-08-23, 6:39pm
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Gila Gila is offline
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Join Date: Mar 17, 2006
Location: Oregon
Posts: 519

Jim, this part of your research is especially interesting to me:

"6 and 8 are very close as far as CFM, mainly limited by the size of the fan, but for a funnel I want increased velocity going into the opening, as well as adequate volume, so I went with 6 inch."

Thanks for sharing .
'...pinpoint the problem, fix it like magic, and then move on.' --AuntD

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Old 2015-08-24, 12:43am
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Speedslug Speedslug is offline
Join Date: Mar 21, 2009
Location: Winnebago, MN
Posts: 2,489

I think your 195 cfm is pushing too close to the lower safe limit for the work you want to accomplish. I think that fighting even a small wind outside would most likely over come this system.

I would first recommend replacing the ribbed flexible ductwork for straight sided hard duct work even at the cone over the torches and on the exhaust side of the fan as well.

The ribs generate turbulence in the flow and will effectively reduce the size of the ductwork by almost two inches and then you are only getting 4 inches of laminar flow.

And is there any way you could translate the 90 degree bends into sloping 45 degree angles?

You currently have 3 each 90 degree bends plus the two 45 degree bends over the torches. That generates a lot of losses that I don't think you can afford with this.

You mentioned that you have access to testing equipment.
Can you run a clamp on amp meter on the wires to the fan?
I am as much in favor as saving money as the anyone else but I have heard things about Harbor Freight equipment that are not encouraging.

I also remember some discussions on my wood working forums about trying to get 3 horse power out of a router on a 15 amp circuit breaker and that the volts and amps math did not add up unless someone installed a 20 amp breaker at the least.

This leaves me concerned that your fan may be running hotter than you would like if it is in fact pushing 2 horse power but I have to say I am inclined to think that the rated cfms on it may be closer to "hot air" than a realistic test would show.

I will be the first to state that flow dynamics is not a field I am thorough versed in.
I learned enough to know that what I planned for my own system was at least three times what I needed and I stopped studying the subject after that.
So all of the above is just my 2 cents and worth what you paid for it.

I am hoping some of our more experienced members will voice their opinions because I learn from each of these questions even when I learn I am wrong.

Good luck with it.
The Zombie Apocalypse is Upon Us.

Last edited by Speedslug; 2015-08-24 at 12:45am.
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Old 2015-08-24, 9:02am
JimW JimW is offline
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Join Date: Jul 14, 2014
Posts: 20

For rigid to work, and I gave it consideration, it would be too bulky and require the tables to be too far offset.
You can see how the velocity is reduced around the perimeter, especially close to the opening. Friction.

Info about funnels is really hard to find. I found that for welding funnels, big units, used for zinc coated metals, pull air in at 2000 ft/m at the opening they don't mention volume. But a dinky little torch is nothing like an arc welder, as far as pollution (for lack of a better word).
For biological hoods, and this, again, is nothing like good 'ole Encephalitis virus, the opening has to be 90-70 ft/m
Neither of those was much help.

In our real world.. we torch with the door closed down to about 9in, I use a block of wood to make sure nothing gets crushed. the side door behind my wife is half-opened.
No smoke can escape from about 2 inches outside the funnel opening and if you stay inside the 8in diameter, between the opening and the torch tip, it pulls the ashes off incense sticks.
I feel safe.

When I get a chance, I'll get the wattage the fan pulls. I have it plugged in to a dedicated 20Amp.
All the lights are 100w equivalent bright white LED at 18watts ea. I run 6.. really bright.

Here's a link to a supplier of ventilation systems, with specs.

Last edited by JimW; 2015-08-24 at 10:28am.
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Old 2015-08-24, 11:33pm
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Speedslug Speedslug is offline
Join Date: Mar 21, 2009
Location: Winnebago, MN
Posts: 2,489


I was just thinking that the flex right over the troches could be replaced with some of those 4 section 90 degree bends.
I have one on the tail end of my system twisted corkscrew style into about a 20 degree angle.
Any place you can reduce the turbulence will up the volume and increase efficiency.

Happy melting.

ETA: Aye, I remember going through that website some half dozen years ago.
My main concerns are about the stated rating of the fan you are using and the classical marketing method of setting up testing practices to with the absolute best possible conditions so the numbers come out smelling like roses but when the same equipment is placed in real world conditions the values drop to 10% of the advertised specs.

I also remember an LE member with industrial hygiene credentials named Dale (I think) and a few others stating that for a barley box or hood arrangement you want a minimum of 125 cfm per square foot of the open face of the work area.

I see ventilation as a classic case of more is better and I myself would not be comfortable unless I had twice or three times what you are working with here.
But I wont belabor the point.

The Zombie Apocalypse is Upon Us.

Last edited by Speedslug; 2015-08-24 at 11:53pm.
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cfm, garage, surface, velocity, vent funnel, ventilation

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