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.
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?