True cost of flex duct?
cnote75
| Posted in Mechanicals on
Hey Folks,
I’ve read many of the reports and advice about flex duct, friction loss, and reduced airflow. What I have not found is how this translates into actual dollars. Can anyone point me in the direction of such a study? Of two systems with one having properly installed rigid duct with short flex runs and the other having rigid trunk and all branch runs in flex with the typical bends, sags, etc. What will be the actual financial operating difference in the two?
Thanks!
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Replies
Your question is a good one, and you may or may not find such a study, or someone may post some calculations. Intuitively, unnecessary static pressure increases operating costs and long-term equipment wear, and degrades comfort at the far end. But regardless of the performance difference between a long saggy flex duct and a more optimal installation, the main point is that bad ducts mean bad workmanship, and the implications go beyond compromised performance. Any contractor that ignores the manufacturer's installation instructions, let alone the proud tradition of "workmanlike", may also have cut corners with more critical but less visible parts of the HVAC system. "Trust Cost", indeed! Even if it saves only pennies, I would take the time--or pay someone--to clean up the installation.
C. Maglio,
In theory, a well-designed and perfectly installed flex duct installation might work fine. In practice, almost all flex duct installations have undersized ducts with imperfectly sealed seams, with runs that are poorly supported, sagging, convoluted.
The main drawback to this type of system is reduced comfort, although if the ducts are poorly sealed, you can certainly have higher energy bills.
There are lots of variables here, and what you want is a conscientious duct system designer and a conscientious duct installer. Just getting the duct system indoors (instead of in a vented attic or crawl space) can be a huge battle with some installers... and if the ducts are outdoors, you've already lost the battle.