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What's The Function Of The Buffer On These Boots?

 
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Old 08-13-2019, 11:45 AM   #1
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What's The Function Of The Buffer On These Boots?


Hi guys general contractor replacing some of this ductwork on an old house, ductwork dates back to the old gravity furnace wanting to know why the ductwork overruns the boot, like a small buffer area just past each vent. Plan to just replace with standard sizes but trying to figure out why it was done that way to begin with.

Picture attached, but if you can't view the boots are large and square, and the square ductwork extends about a foot past the boot and terminates.
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Old 08-13-2019, 12:00 PM   #2
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Re: What's The Function Of The Buffer On These Boots?


If you are referring to a cloth or rubberized type of material it is to reduce vibration and allow the duct to flex.

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Old 08-13-2019, 12:11 PM   #3
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Re: What's The Function Of The Buffer On These Boots?


I'm guess the box extends so the hole for the boot can be cut later. Just another way to do it.
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Old 08-13-2019, 12:11 PM   #4
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Re: What's The Function Of The Buffer On These Boots?


Griz, the whole thing's (rusted) sheet metal. I was wondering why the ductwork sticks out past the register. It's got to be intentional because they're all like that in the house. I think it must be something to do with the way the air would move in the old gravity furnace system but I can't for the life of me figure out what or why.
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Old 08-13-2019, 01:47 PM   #5
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Re: What's The Function Of The Buffer On These Boots?


It has nothing to do with airflow, it's just fabrication/installation sequence.
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Old 08-13-2019, 07:08 PM   #6
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Re: What's The Function Of The Buffer On These Boots?


I was once told it was for dust, the dust will collect there instead of blowing into the room. Not sure if true or not but gravity air systems were very dusty.
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Old 08-14-2019, 09:38 PM   #7
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Re: What's The Function Of The Buffer On These Boots?


Quote:
Originally Posted by rrk View Post
I was once told it was for dust, the dust will collect there instead of blowing into the room. Not sure if true or not but gravity air systems were very dusty.
They aren't because they don't blow air.

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Old 08-16-2019, 05:15 PM   #8
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Re: What's The Function Of The Buffer On These Boots?


It would maximize the temperature of the air leaving the boot into the room, the colder air returning in the bottom half of duct.

No change in elevation no "chimney effect"....

And a tee would always flow more then the same sized 90 degree elbow,

plus I'd think it would be an "anti-reversion" device to reduce back flow when the bimetallic controlled damper closed the air feed to coal fire....

You wouldn't want the gravity furnace running backwards, hot up the floor return, cold returning through the ductworks...
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Old 08-29-2019, 11:30 AM   #9
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Re: What's The Function Of The Buffer On These Boots?


My guess is that it's a standard section of "rec-duct" and the installers didn't want to cut it down.



After all, it appears there's plenty of space for it, and who wants the left-overs on that?
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Old 08-29-2019, 08:27 PM   #10
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Re: What's The Function Of The Buffer On These Boots?


Not suppose to tap off the very end of the duct. As it can cause turbulence.

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