How Many Take Offs Can You Put On An 8x20 Trunk Line? - HVAC - DIY Chatroom Home Improvement Forum


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Old 05-09-2009, 05:31 PM   #1
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how many take offs can you put on an 8x20 trunk line?


I have a question about trunk/plenum lines. how many take offs can you put on an 8x20 trunk line? An 8x18? I had a guy get me all the material to do the install and the design for it, but he is having dificulty getting his drawing back to me so i can see/figure out how to run it all.

How far from the end of the trunk do you have to be on the last take off?
Another question, in a 15' x 17' room, how many vents? since i don't have his drawing, i'm thinking 4 because it has 2 out side walls and 2 windows one facing north and the other west.( using 6" round branch).

Thanks for the time and any help you may provide.

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Old 05-09-2009, 05:39 PM   #2
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how many take offs can you put on an 8x20 trunk line?


I believe that the last takeoff should be a minumum of 18" from the end. Others can help with supply duct CFM requirements for the room. Just be sure to allow for return air ducting as well. Good Luck.

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Old 05-09-2009, 05:49 PM   #3
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how many take offs can you put on an 8x20 trunk line?


Depends how long the duct is.

As much as that sounds like a S.A. answer.
You don't give enough info to tell you anything.

As far as how much air to that 15x17 room. Hard to say, ithout knowing where you are, and how much insulation it has.

Doubt it needs 4 supplies though.
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Old 05-09-2009, 06:49 PM   #4
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how many take offs can you put on an 8x20 trunk line?


house is in northeastern ohio. r-19 cieling and r-13 walls. 40" of 8x20 vertical to horizontal 90 to 5' run of 8x20 to horizontal 90 another 5' of 8x20 then reduced to 8x18 for another 8'. looks like an L. retro fit is fun! hope that might help
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Old 05-09-2009, 06:55 PM   #5
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how many take offs can you put on an 8x20 trunk line?


i forgot to mention the return is in the 15'X17' room.(16"x25" filter box) with louvered doors on the closet where the furnace is located in the adjoining hallway
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Old 05-09-2009, 07:17 PM   #6
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how many take offs can you put on an 8x20 trunk line?


2 6" at 80CFM each would be plenty for that room.

With those ells in that 20x8 duct. It makes it very restrictive.

Hope your not trying to move more then 700 CFM.

4 max take offs at 70 to 90 CFM per 6" take off.
3 at 100 CFM each.

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