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Old 06-17-2010, 06:26 PM   #46
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New 22' Trunk Line


You'll find a fair number of your rooms upstairs will be better off with 7". Better off not using 5" on the first floor. First floor needs more heat in winter. Second floor more cooling in summer.

Its easier to install dampers in the supply runs and throttle them down for balancing. Then it is to get more air out of a smaller pipe.

The CFM's are generally ok in HVAC Calc.

A copy of Manual D and a duculator will help you figure out what size ducts to runs.

Manual D will help you determine what friction rate to use. And eh Duculator will tel you what size duct will have that friction rate for that CFM.

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Old 06-17-2010, 11:22 PM   #47
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New 22' Trunk Line


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Originally Posted by beenthere View Post
A copy of Manual D and a duculator will help you figure out what size ducts to runs.

Manual D will help you determine what friction rate to use. And eh Duculator will tel you what size duct will have that friction rate for that CFM.
Is there maybe a typo in the above?

That or I'm confused

I managed to pull out each room cfm (HVAC-calc) and picked an existing duct size (7 inch) and was able to figure out the friction rate based on the length of the run.

Now what do I do with all the friction rates?
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Old 06-18-2010, 02:54 AM   #48
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New 22' Trunk Line


Now u try to stay as close as to those friction numbers.

Never seen a resi duct redesign that didn't have to scarfice somewhere to make any kind of an improvement to gain optimal airflow and till be quiet enough
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Old 06-18-2010, 04:52 AM   #49
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New 22' Trunk Line


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Originally Posted by unixb0y View Post
Is there maybe a typo in the above?

That or I'm confused

I managed to pull out each room cfm (HVAC-calc) and picked an existing duct size (7 inch) and was able to figure out the friction rate based on the length of the run.

Now what do I do with all the friction rates?
How did you determine what the length was. What did you use to determine what the equivalent length is of the register boots, and the take offs, and transitions in the duct.

How did you determine what the friction rate was? Did you measure the actual CFM through each of those pipes, and then measure the pressure drop for each of those pipes?

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