do these sound right for cfm rating of flex duct?
for instance I have been told 6'' flex is 110 cfm
this says 6'' flex is 75 cfm
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do these sound right for cfm rating of flex duct?
for instance I have been told 6'' flex is 110 cfm
this says 6'' flex is 75 cfm
the cfm depends on the static the system is based upon. Usually a 6" round is about 120cfm using galvanized pipe. With flex pipe, there is a greater resistance to airflow so the cfm may be less with a higher pressure. I would anticipate that you would get somewhere between 100 and 120 cfm through the 6" flex. It's not that 6" flex or round pipe "is" or "isn't" a certain cfm. The size pipe is 'capable' of a certain airflow at a certain static pressure.
Can you expand on the context of your question?
All the best, John.
There is also a FPM limit for each type of pipe. I'm not sure why (noise, turbulence, duct abrasion...), but Manual D lists these limits. Smooth metal duct has the highest limit, and flex the lowest.
So there are two limits: velocity (feet per minute), and static pressure loss. You can't exceed either one.
Cfms for 6" duct are what they are .depending on the duct system.
First a Manul D to determine the actual Friction Rate (FR)when designing the duct system.
6" round metal
@.04FR=67 cfms
@.06FR=82cfms
@.08FR=96cfms
@.10FR=107cfms
If flex it wil be less cfms in each case.
The more resistance,turns,length,etc., that the duct system has the Lower the FR will be.
There is a ductulator for flex.
Nice specs....how many feet are those based on?.....like a ductulator is based on per 100 feet after calculating in turns and elbows to arrive at a distance. The reason I ask is that I couldn't imagine running 100 feet of running flex on a run and figuring 15 feet per turn and hoping for even achieve 82 cfm
The FLEX #'s I posted are right off the FLEX ductulator. Flex has different rules:
Flex Sizing is based on 20' of EQUIVILENT duct
EQUIVILENT means each 90 = 10' , when 40' EQUIVILENT is met, you have to increase duct size X 1 size... 2' or less = decrease X 1 size
Most of the installations I find with radically excessive duct statics are cause by misinformed contractors using a regulator DUCTALATOR instead of a FLEX ductulator.
I wish I had access to a flex ductulator so that I could prove to my boss why I want to over size runs instead of going with tin standards ....all I can try to do is use logic. Many times logic loses to profit.
Disturbing but true ----
The data is available @ www.atcoflex.com
or call them @ 800-877-3828 and buy a ductulator
Thank you for the link coolguysfl!