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Duct Construction and Uses
Discussion in fabricating and use of products that move air including spiral pipe, duct board and typical sheet metal work.
       


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  #1  
Old 09-05-2004, 12:57 PM
jessea1015 jessea1015 is offline
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Default air through elbows

We have a chart at my shop that tells how many feet different kinds of fittings are worth. It says an elbow with a square heel and throat has the same amount of air loss as an elbow w/ a radius heel and square throat.Is this true? Excuse me if my lingo is not correct.
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Old 09-09-2004, 09:08 AM
CadMan CadMan is offline
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I read thru the SMACNA Duct Design book and all I found was that a radius throat is about 70% better airflow than a standard 90. Couldn't find anything about the heel though. I was interested in where you got this chart and where I might get one.
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Old 09-09-2004, 02:36 PM
tazman tazman is offline
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Radius is always better then square, when it is about the air resistance.
We ALWAYS use elbows with a radius. Except for the inner radius, when there is too less space we use square.

I have a simple mind and see it simple. Air likes a quiet easy ride, and not a ductsystem like rollercoaster!
Also watch out for noises!!! I never here about sound in here. There are some golden rules.
One of them is sharp edges, they can cause some noise.
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Old 10-20-2004, 02:52 PM
bordontn bordontn is offline
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Be careful of those square throats on a radius elbow....I'm posting part of a chart which shows the resistance in feet of duct..
the itinerant tinker a.k.a. bordontn
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Old 10-27-2004, 05:26 PM
Gate Gate is offline
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A vaned square throat/heel ell is better for airflow than a radius heel with square throat. If you vane this configuration you need to run full vanes evenly spaced...

peace,
- Gate
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Old 03-05-2008, 09:25 AM
energystar energystar is offline
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I was told by an engineer that a radius throat with a square heal is the way to go. It's better than a sq/sq with no vanes
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Old 03-05-2008, 03:36 PM
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Better then vanes? I don't think so. The radius throat and heel is great way to fab elbows, and you really want to learn more about the radius to width ratio for maximum air flow or air flow with the least resistance. If you can't use a radius throat, you should probably consider vanes to help the air flow around the corner.
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Old 03-05-2008, 07:53 PM
legacy legacy is offline
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We once had a guest speak at a union/management committee day, he was representative from the ITI (body that governs all SMWIA apprenticeship programs). ...Anyway, he was retiring from the ITI and was moving from CA to TN and was having a house built. On one of his final trips to check on construction, he noticed that the HVAC constractor had used all srare throat/ radius heel 90's. He made the take them out and replace them with full (1-1/2X) radius 90's where they would fit and sqaur with vanes where they did not.

I have made sq throat/radius heel for people that have walked into my shop looking for duct, but have never made that fitting for one of my jobs.

Just like a point to point (no miter) offset, if you measure the distance from the inside of a square throat to the mid point of the radius heel of a sq/rad 90, its got to choked down by at leats 10%-15% I would think.
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Old 10-21-2008, 03:50 PM
cactassdupree cactassdupree is offline
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Antone heard of double Vanes? they are 2 pcs. per vane
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Old 10-21-2008, 06:23 PM
device device is offline
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the aerofoil type..
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