I have central ac in my home and at some point the kitchen was redone, blocking an existing vent permanently. The flex HVAC ductwork leading to the vent (probably 8 feet of it) is still there. Should I remove this ductwork to improve efficiency? How much efficiency are we talking about?


  • @FreeMan correct my dishwasher and cabinet are nice and warm in the winter.
    – Pinch
    Commented Nov 29, 2020 at 2:47

2 Answers 2


Having a dead end is actually a good thing. It will not harm your efficiency at all. You see this more often on large trunk lines, you will notice that the trunk goes past the last duct opening by at least a foot. This buffers the flow and will make the registers on the same trunk have similar flow depending on taper and such. If the vent was removed I would consider relocating it so the home is balanced.


If the duct is blocked off at the end so that no air flows through then it should have minimal effect on the system. Removing it should not be expected to make any efficiency improvement.

On the other hand, if that duct is just lost in the floor or ceiling somewhere and is discharging conditioned air into who-knows-where, then yes you might gain some efficiency by blocking/removing it so that the conditioned air goes into occupied rooms instead.

It's impossible to say how much efficiency might be improved. It depends on what fraction of the system's total air flow is blowing out through this duct and whether it escapes into the environment or stays reasonably well inside the house envelope.

All that said: it is nice to remove abandoned wiring, plumbing, duct work, etc when it's feasible to do so and there's confidence that it wouldn't be used again in the future.

  • The only place I would suggest a change is the home is no longer balanced without the duct being used so depending on the flow curve it may cost more to move air but it would be a small number.
    – Ed Beal
    Commented Nov 30, 2020 at 21:07

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