# Thread: Friction Loss

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## Friction Loss

For new installs, do you rely on a standard figure or are you using a formula to arrive to a given factor?

2. I beleive I read on the Udarrel site (one of the Pro's here) a recomendation of 0.05 or 0.06 water column per hundred ft of duct.

I'm shooting for lower static pressure so my new duct sytem is being designed closer to 0.04.

Key1

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I rely on ACCA manual J, D, S, T, RS, Quality Install, Right Suite Universal, and some others to come up with the correct friction loss and design.

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I know that manual D provides the formula for sizing and such, however I don't think it addresses the formula to obtain or verify the correct friction loss.

Aside from a rule of thumb method, how is friction loss verified?

key1cc: I could be wrong, but using .5/100' as a standard sounds incorrect. I mean I could be wrong, but if that is true you're saying a 6" round will flow around 220CFM. I have always been under the belief that a 6" has a flow closer to 110CFM. Referencing the ductalator, that equates to a friction loss of .1, which is 100% variation from .5

Now I am not a sheet metal guy, and I am not saying that using .5 as a standard is incorrect, but it dose seem right to me. Frankly this is why I have asked the question to begin with.

Without knowing how to arrive to the correct FL, you are essentially guessing.

5. Key posted .05", NOT .5"

And Manual D does have the FR formula.

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Originally Posted by beenthere
Key posted .05", NOT .5"

And Manual D does have the FR formula.

Thanks for the correction, I overlooked the extra digit. I suppose that using.05 dose make more sense in that it would yield a more conservative CFM flow, and perhaps build in some redundancy to help prevent A coil freezing on designs that may not have too much restriction.

One of the reasons I started the post is that I cannot find my book. It has been years since I have seen it. Can you bring me up to speed on the formula?

7. (asp*100)/tel=fr

Eg: (.18*100)=18,/295=.06"fr

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Originally Posted by beenthere
(asp*100)/tel=fr

Eg: (.18*100)=18,/295=.06"fr
Thanks

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