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| Safety -- Make sure you are safe! |
2007-04-03, 7:03pm
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birdergirl ~o~
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Join Date: May 17, 2006
Location: Unorganized Territory
Posts: 2,002
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Is my fan too big?
My fan is very close to being installed and after talking with a friend I'm afraid it's too big ( of there is such a a thing) :
My studio is 6.5 X 8.5 feet with a 7.6 foot ceiling.
My squirrel cage fan is 800 CFM
Make up air will come from a part of the house not often heated in the
winter.
Is this going to inhale everything off my tabletop ( glass, silver leaf etc.)
And give me a hairdo like Marge Simpson? 
And most important.. Is the warm air going to be taken out so fast that I will have trouble staying warm ( in the freezing cold Maine winters?)
Thanks 
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~raised by wolves~sleeps with foxes~cooks for crows~feeds the bears~scrabbles with squids~antisymmetrical~politically agnostic.
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Torchering glass since spring '06~ gold cricket & oxycon!~
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2007-04-03, 7:48pm
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reaction junkie
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Join Date: Jun 11, 2005
Location: Edmonds, WA
Posts: 1,119
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Sally, I think the people who will know the answer to this are going to want to know what size hood you will be using - if it's big then I think 800 is ok, though it does sound a bit overkill (to me, no expert!). And you'll need to have make-up air that is coming from outside - you can't use inside air for make up even if you fan was smaller.
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Pam
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2007-04-03, 7:55pm
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In search of her path....
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Join Date: Jun 05, 2005
Location: North Seattle, WA (use to be Fort Wayne IN)
Posts: 7,285
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the 800 you should be fine with....but really it depends more on how far your duct work is running and how many twists and turns your duct takes and what kind of duct your using smoother or corrugated (smooth hard duct is best).
I dont know all the mathmatics of it I know Mike A. has them though.
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2007-04-03, 8:00pm
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I'm a lilac!
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Join Date: Jun 09, 2005
Location: Portland, Oregon
Posts: 8,793
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My fan is a two-speed squirrel cage that runs at, I think, 600 CFM on low. I can't really remember now, I bought it a while ago. It's far enough off the workbench that it doesn't suck up silver (unless I let some get airborne) but it does make it hard for me to stay warm in the winter. I have a gas heater in my studio, and with the fan off it would be way too hot in 10 minutes. Turn the fan on, and 5 minutes later it's chilly, even with torch, kiln, and heater going.
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2007-04-03, 8:05pm
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What, Me Worry?
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Join Date: Jul 09, 2005
Location: Texas
Posts: 343
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Well... if it runs at 800 CFM the room will be emptied every 30 seconds... so yes... you will have a 'heating challenge'.
Blue is right... Mike will want to know the hood size and ducting... so post it up  .
Me
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2007-04-04, 5:30am
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birdergirl ~o~
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Join Date: May 17, 2006
Location: Unorganized Territory
Posts: 2,002
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Hood size 2"x 3"
Duct size 8" ( two 90° turns ( unavoidable) /hard pipe.
Sorry forgot to add:
The part of the house where my MU air is coming from will have a door cracked open where my hoses come through from out side so there is an outdoor air source~ just hopefull a bit pre-warmed a tiny bit before it comes into the studio.
Thanks everyone!
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~raised by wolves~sleeps with foxes~cooks for crows~feeds the bears~scrabbles with squids~antisymmetrical~politically agnostic.
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2007-04-04, 6:21am
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In search of her path....
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Join Date: Jun 05, 2005
Location: North Seattle, WA (use to be Fort Wayne IN)
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Cadia how far is the duct running? how far does it run from your hood to the first and 2nd turns till it gets outside? that makes a difference too....
Also is the 8" the actual exit size from the fan or did you reduce the whole down to 8" to fit the duct?
All this will make a difference to the actual CFM's your fan will pull just trying to help so all the info is here when Mike or someone a bit more mathmatically knowledgable steps in
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2007-04-04, 6:41am
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Safety ALWAYS
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Join Date: Jun 10, 2005
Location: Sauk Rapids, Minnesota
Posts: 2,401
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I hope you mean 2 feet by 3 feet and not 2 inches by 3 inches 
The min/max numbers are 100 and 125 CFM per square foot of hood. Your hood is 6 square feet, so your fan should be in the range of 600 to 750 CFM. 800 is slightly, repeat SLIGHTLY oversized, but that's not a concern.
My biggest concern is your statement that make up air will come from a part of the house not often heated in the winter....
Make up air *ABSOLUTELY POSITIVELY* has to come from outside. You *CANNOT* use air from the house for make up air.
Room size has nothing whatsoever to do with sizing of the fan.
One thing you can do to decrease the effect that outside air is going to have on your room temperature is to duct the fresh air directly to your workstation and bring it up through the bench top.
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2007-04-04, 8:31am
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Safety ALWAYS
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Join Date: Jun 10, 2005
Location: Sauk Rapids, Minnesota
Posts: 2,401
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I totally disagree. Squirrel cage fans with an external motor are far superior to in-line fans for many reasons.
1) In-line fans have the motor in the airstream. They rely on air-over cooling. If the air stream exceeds the design spec, usually 140 to 150 degrees F, the motor will quickly fail. While this may not be an issue on smaller torches like the minor, it *IS* an issue on larger torches, from the Phantom on up.
2) Many in-line fans like those mentioned above are designed as "duct boosters", for pushing HVAC air into low flow areas, usually from long duct runs causing a loss of air flow. They are designed to be used with air that is already moving.
3) Squirrel cage fans are a much better design and have higher static pressure tolerances because they can use a properly sized motor. In-line fans have natural restrictions on the size of the motor that can be used with them, squirrel cage fans do not.
4) The only time I recommend in-line fans are for large volume flows for multi-workstation installations where it is either not desirable or impossible to run multiple squirrel cage fans.
5) Squirrel cage fans are highly flexible and can be used in a variety of configurations and locations. In line fans can only be installed one way.
I also question your comment on "true CFM". There is no such thing as "true CFM". CFM is CFM is CFM. As with all air moving equipment, CFM varies with the static pressure of the entire system. This is true of ANY fan, including the fans you mention in your writing. The only difference is that a squirrel cage fan will have a wider range of static pressures under which it can operate under than an in-line fan does because of the motor sizing issue I mentioned above.
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2007-04-04, 9:06am
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birdergirl ~o~
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Join Date: May 17, 2006
Location: Unorganized Territory
Posts: 2,002
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Make up air etc.
Yes Mike, 2 feet by 3 feet is the hood size!
Duct will turn 90° after coming up through the hood, run 2 feet turn 90° then run 4 feet to pass outside.
The duct going to the fan is 8" then as it passes into the fan it reduces to a 7"
size. The part of the house where my MU air is coming from will have a door cracked open where my hoses come through from outside so there is an outdoor air source , there will be about a inch-1.5 inch by 6.6 feet of opening to outside~ just hopefull a bit pre-warmed a tiny bit before it comes into the studio.
Thanks all for helping me get all my ducts in a row !
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~raised by wolves~sleeps with foxes~cooks for crows~feeds the bears~scrabbles with squids~antisymmetrical~politically agnostic.
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Torchering glass since spring '06~ gold cricket & oxycon!~
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2007-04-04, 9:23am
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Safety ALWAYS
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Join Date: Jun 10, 2005
Location: Sauk Rapids, Minnesota
Posts: 2,401
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I would try to make sure that the door is open wider than that.
Don't use a duct reducer before the fan, use a duct plug and cut the 7" hole in that. A reducer is going to increase your static pressure significantly, but using an 8" duct plug with a 7" hole will not. Yeah, I know that may not make sense, so here are the mechanics:
A duct reducer decreases the size of the duct prior to entrance into the fan. There is a narrowing of flow, which creates turbulence and turbulence creates back pressure.
If you use an 8" duct plug and cut a 7" hole in it, and mount the cut duct plug directly to the fan, there is no reduction to create turbulence. The fan draws air directly from the 8" duct through the 7" hole.
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2007-04-04, 9:48am
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birdergirl ~o~
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Join Date: May 17, 2006
Location: Unorganized Territory
Posts: 2,002
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In case I am not saying what I mean here is a pic with dimensions-
right now I have the 8" duct fitting on the out side of the 8" ring - the reduction of size is built into the fan. The hole going into the fan is 5" ( sorry for the previous 7" quote) Hope this clears it up. (?)
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~raised by wolves~sleeps with foxes~cooks for crows~feeds the bears~scrabbles with squids~antisymmetrical~politically agnostic.
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2007-04-04, 9:52am
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Safety ALWAYS
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Join Date: Jun 10, 2005
Location: Sauk Rapids, Minnesota
Posts: 2,401
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Well, in this case Trey, yeah, I do know better. I've been involved with industrial ventilation far longer than I have been selling eyewear for lampworkers. I've designed fan selection software for a leading industrial air moving company, so I think I know just a teeny tiny bit about fans, fan design and ventilation.
I also disagree with your comment about building temperatures in your duct. Go visit a foundry sometime and feel how hot their exhaust ducts are. You are making meaningless comments about something you know very little about. What works for you (and I'm glad it does) may not and probably will not work for someone else.
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2007-04-04, 9:53am
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Safety ALWAYS
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Join Date: Jun 10, 2005
Location: Sauk Rapids, Minnesota
Posts: 2,401
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Sally ----- ah!!!! Got it! Excellent! No worries on the reduction then.
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2007-04-04, 10:59am
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Gentleman of Leisure
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Join Date: Jun 10, 2005
Location: A Little Bit West of Yosemite Valley
Posts: 5,200
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Did I miss something.... Seems that some post may have been deleted?
Dale
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2007-04-04, 11:12am
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Senior Member
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Join Date: Nov 28, 2006
Location: New England
Posts: 1,096
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Mike, you should've quoted. I would have loved to have read this. Why do people feel the need to act like experts when they're not, argue, and then delete??? Is ist because they feel like idiots now? I guess so.
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2007-04-04, 11:15am
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Safety ALWAYS
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Join Date: Jun 10, 2005
Location: Sauk Rapids, Minnesota
Posts: 2,401
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ROFLMAO --- well, the next time this person makes a post that I am going to respond to, you betcha I'm going to quote him.
'Twas Trey Cornette, btw........
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2007-04-04, 11:18am
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DSDWC
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Join Date: Nov 04, 2005
Location: Born in the backwoods. Raised by a bear
Posts: 1,268
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I Just chose not to argue with King A.
Its just not worth it 
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2007-04-04, 11:31am
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birdergirl ~o~
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Join Date: May 17, 2006
Location: Unorganized Territory
Posts: 2,002
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Well thank you all for your help - you made Ed my carpenter (see below !) very happy - He was waiting in the wings until I had the answers!
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~raised by wolves~sleeps with foxes~cooks for crows~feeds the bears~scrabbles with squids~antisymmetrical~politically agnostic.
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2007-04-04, 2:43pm
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Gentleman of Leisure
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Join Date: Jun 10, 2005
Location: A Little Bit West of Yosemite Valley
Posts: 5,200
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Quote:
Originally Posted by Trey Cornette
I Just chose not to argue with King A.
Its just not worth it |
If you can't run with the big dogs, stay on the porch.....
Let me explain.... Some time back when LE first came into existence, I made some comments, and received some really bad reaction about my comments. So my thinking was to delete the messages or edit them out, to ease the situation. To my surprize the castigation I received for trying to remove the offending remarks were worse than if I had let them remain....
So... IF you comment on something and its proven wrong, its best to say "I made a mistake in my post and.....". When you try to remove them and gloss them over, it just looks poorly on you....
Dale
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