Working on a job, and typical me I start asking questions versus just go with the standard of what I know. Reading some articles on duct design, and now here I am. Question, I got my ductulator right here, and question on static pressure, and velocity. What should I be using? Is there a difference between residential sizing and commercial sizing? What static pressure should I be using to size my ductwork? Normal a .10? If I change static pressure how does it work? How does velocity work with my cfm? Thanks for your help guys. I read a few articles and always have more questions than when I first started
I don't believe you will find an option for .10 static pressure on your ductulator. what your likely looking at is friction rate.
Friction rate is calculated not picked, based on the total equivalent length of you duct work and the available static pressure your blower can work against.
Google "The ACCA Wedge" you will find a good description on how to size your duct work
"The only way in which a human being can make some approach to knowing the whole of a subject is by hearing what can be said about it by persons of every variety of opinion and studying all modes in which it it can be looked at by every character of mind.
No wise man ever acquired his wisdom in any mode but this."
John Stuart Mill
"The only way in which a human being can make some approach to knowing the whole of a subject is by hearing what can be said about it by persons of every variety of opinion and studying all modes in which it it can be looked at by every character of mind.
No wise man ever acquired his wisdom in any mode but this."
John Stuart Mill
Got good info yesterday for determining friction rate to use in sizing ducts. After weeding thru a hundred different opinions and answers ill apply it in the real world and go from here. Thanks guys
Another question, still dicking with this ductulator. If I line up the standard .10 and my cfm I'm supposed to go look at the duct size. Using this rule of thumb, I look at 1200 cfm @ .10 and I see the velocity is 1000 fpm. Which is higher than the recomended 600-900 fpm. Am I using this ductulator incorrectly? Or is velocity a different method to use versus friction rate?
Basically with ductulator at that friction rate this much air (cfm) will be moving this fast(fpm) and will be loosing. 0.1" static each 100 equivalent feet(factor in the fittings).
Got good info yesterday for determining friction rate to use in sizing ducts. After weeding thru a hundred different opinions and answers ill apply it in the real world and go from here. Thanks guys
Another question, still dicking with this ductulator. If I line up the standard .10 and my cfm I'm supposed to go look at the duct size. Using this rule of thumb, I look at 1200 cfm @ .10 and I see the velocity is 1000 fpm. Which is higher than the recomended 600-900 fpm. Am I using this ductulator incorrectly? Or is velocity a different method to use versus friction rate?
No your not using the ductulator right. You can't pick a random friction rate. you need to calculate it based on the total equivalent length of your run.
The duculator does not know if your looking for the size of a straight run 100 ft long or a run 100 ft with 10 fittings in it. If you just pick .10 friction rate it will size the duct the same for 100' straight duct or 100' with 10 fittings
"The only way in which a human being can make some approach to knowing the whole of a subject is by hearing what can be said about it by persons of every variety of opinion and studying all modes in which it it can be looked at by every character of mind.
No wise man ever acquired his wisdom in any mode but this."
John Stuart Mill
Or is the FPM incorrect of 600-900? The more articles u read, the more different opinions and answers u get, and then ur confused more than ever. I'm gonna do my calculation like article u sent and size my ductwork accordingly then see what the real world tells me and quit reading **** lol
Ok so people that just use the .10 on ductulator are doing it wrong. So I'll determine my duct length and pressure drops and come up with the correct friction rate and size my ductwork accordingly
That's what I'm trying to determine. I see people just grab a ductulaor and pick the .10 and say here's your duct size. Length, fittings etc etc how can anyone just come up with the right size. I got the formula method down, thanks, now just trying to determine how the .10 method doesn't work. Appreciate your help guys. Spent all day Sunday on this crap, and this am. I'm hat much smarter now
Reply With Quote
Originally Posted by Iceman_pdx
