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Little Shop of Duct Design Horrors

Stumpy, The Duct Amputee, Making A Mess Of Conditioned Air Distribution In An Unconditioned Crawl Space

And now for a little Friday fun, here’s one of my favorite duct design failures. I call it Stumpy.

What’s happened here is that the contractor who retrofitted the duct system just cut this one off mid-run. The problem is that the duct leakage will be high, and the duct will eventually just fall apart completely. Notice they used duct tape on the end to ‘seal’ it up. Unfortunately, although duct tape is good for many things, sealing ducts is not one of them.

What’s wrong with that?

This duct amputee was just the tip of the iceberg in the home’s duct system. The limp flex duct hanging over Stumpy’s parent was supposed to carry air all the way to the back of the house but was so poorly installed that the master suite stayed uncomfortable most of the time. The leakage in the duct system was, as you might expect, really high (506 cfm25, for you duct testers out there).

It’s fine to retrofit a duct system and stop using a run, but the proper way to do that is to cut it off where it first starts, not halfway down the run.  In this home, there were so many problems, the best solution would be just to rip all the ducts out and start over. The first step would be an overall HVAC design that includes Manual J and Manual D calculations and an actual duct design. Imagine that!

Sadly, the unsuspecting homeowners actually paid for this. An HVAC contractor left them this little present.


Allison A. Bailes III, PhD is a speaker, writer, building science consultant, and the founder of Energy Vanguard in Decatur, Georgia. He has a doctorate in physics and writes the Energy Vanguard Blog. He also has a book on building science coming out in the fall of 2022. You can follow him on Twitter at @EnergyVanguard.


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This Post Has One Comment

  1. Unfortunately, Ted, I wasn’t
    Unfortunately, Ted, I wasn’t involved in the work to fix this house, so I don’t what they did. I’m pretty sure, though, that they didn’t do the heating & cooling load calculations or the duct design. I’d recommended that they rip out the ducts completely and start over, but I doubt they did that either.  
    Sadly, this was NOT a DIY job. It was done by an HVAC contractor during the remodel that happened a few years ago.

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