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Go Back   Lampwork Etc. > Library > Safety

Safety -- Make sure you are safe!

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  #1  
Old 2021-05-17, 9:58am
eastcoastbeginner eastcoastbeginner is offline
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Default Duct reducer?

Hi, I'm new here

I am setting up a small workshop in my shed, and have a question about duct size for ventilation - the hood I've got has a 7" duct opening. As most inline fans are widely available in 6" and 8" versions, I'm wondering how to join 6" or 8" ducting to the hood. If I bought an 8" inline fan and 8" ducting, what would happen to the CFMs if I add a reducer to 7" right where the ducting joins the hood? Will that kill the power of the fan? Should I go with a less powerful 6" fan with 6" ducting instead, and add a duct increaser right where the ducting joins the hood to fit the 7" opening? I'd rather do the first option if it lets the more powerful fan still do its thing, but if by reducing the opening to 7" I'm dropping the CFMs of the fan, then maybe I should just buy a smaller fan and go with 6" ducting?

Ducting will be minimal - 2-3 feet of ducting above the hood plus the fan plus a 90 degree elbow to vent outside.

Thanks for any insights!
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  #2  
Old 2021-05-17, 10:40pm
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Speedslug Speedslug is offline
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My first thought is; Is there any possibility of getting the hood opening increased from 7 inches to 8 inches.
Lots of heating, ventilation and air conditioning companies can snip the hole size easily for a price.
They do it all the time and hardest part is getting the hood to them (much cheaper) or them to find a room in their schedule to come to the hood (read: house call $$$).


Any change in size effectively turns the entire rest of the ducting after the change to that size.
A smaller size will increase the speed of the flow through the restriction and puts strain on the motor doing the propulsion. Most motors can handle a little extra strain but it will shorten how long that motor will live.

If you then go back up in size to the size before the restriction the flow will slow down and some of the particles suspended in the flow will fall out and coat the inside of the ducting.

There is a lot of discussion about ventilation in the safety threads here.

Short answer; since you aren't setting up an industrial 24/7/365 factory then yeah, go for it.
If the fan is at the wall and outside is just an elbow the same size of the fan outlet you should be fine.
Keep the same size duct from the hood to the fan and then the same size from the fan to the outside dump.

If you get seriously addicted to molten glass you would be better off getting the hole on the hood increased and running the same size duct on the whole run.

Bigger CFMs is better when you can and don't believe any CFM marks on bathroom fans. They often flat out lie and aren't even a quarter as good as they say they are. They just move shower steam and farts so no one calls them on it.
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Last edited by Speedslug; 2021-05-17 at 10:42pm.
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  #3  
Old 2021-05-18, 3:43am
eastcoastbeginner eastcoastbeginner is offline
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Thank you this is very helpful. I didn't think about contacting a metal worker to enlarge the hole - that would totally be the best idea, so I can set things up properly from the start. I will call someone today and see what the possibilities are.

My intended fan (its sitting in my amazon shopping cart right now) is the AC Infinity Cloudline S8 that gets good reviews - I'll do a search here on the forums to see if anyone else has had success with that.

Thanks again!
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  #4  
Old 2021-05-18, 6:47am
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Speedslug Speedslug is offline
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And welcome to your addiction.

I suggest buying a little cheap glass to begin with.

You body, torch bench, posture, chair, lighting, cooling, heating and ventilation for your own comfort, where to put the drinking water and the quench bowl are all just some of the stuff you are going to be learning what works for you in the first weeks of playing with glass.

You don't want to add spendy glass into that mix to begin with because that makes it kind of like trying to learn to ride a bicycle in a tuxedo. You wind up stressing out instead of enjoying the play aspect and remembering to play is important.

Enjoy.

Be sure to add your name and address to the Random Acts of Glass Kindness list so we can keep track in case the computer systems takes a hiccup or something.
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  #5  
Old 2021-05-18, 11:00pm
eastcoastbeginner eastcoastbeginner is offline
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Thanks! I definitely plan to start with cheaper glass until I gain confidence I won't ruin the good stuff. Looking forward to getting started!
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