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rick31797 03-07-2013 03:16 PM

Need help with duct work
As the pictures show this is a mess,i was told because these run offs are so close to the end, there is no static pressure.. there fore i am not getting the heat i need in other ares of the house.

I have a piece of hot air duct, 8x12, so that i can extend this 3 feet, that's as far as i can go, there is a wall.
I would like to straighten a couple of the runs and would like to move them closer to the end of the new piece i am putting in.
My question is how close to the end of the 8x12 hot air duct can i get, before i end up messing it up, like it is now. Thanks

Marty S. 03-07-2013 05:11 PM

At least 18" away from the end.

rick31797 03-07-2013 05:15 PM

Duct work
Exactly what i needed , much appreciated, thanks

jagans 03-07-2013 08:02 PM

Someone on another post said that no takeoffs should be installed closer than three feet from the end of the main supply duct. Here you say 18 inches. Thats half. Which is it, 36 inches, or 18 inches, and what is the reason?

:whistling2::whistling2::whistling2::whistling2::w histling2:


REP 03-07-2013 09:29 PM

18 inches is fine.While you have this opened up you might want to install some balancing dampers on each round run.

rick31797 03-08-2013 10:43 AM

Duct work
I am finding the heat is not balanced through-out the house, the ductwork that goes to the front of the house is fine, the ductworking coming off the back of the furnace is not, plus the rooms are larger, so i will change the ductwork at the back as in the picture, i am not sure i would want any dampers as i need more heat.

i am thinking of putting in a damper at the front side of the furnace to force more air to the back.. the duct work at the front is 16 x 8, i would need to open that up and install a damper there.

beenthere 03-08-2013 03:20 PM

Those take offs being at the end of the duct like that, aren't your heating problem. More likely the trunk line is under sized. take offs at the end of the trunk line cause turbulence, not loss of static pressure.

In crease your trunk line size, and use a warm air start collar to attach it to the plenum.

rick31797 03-08-2013 03:33 PM

Duct work
I have had a few people in , and everybody says something a bit different, i do agree with you, maybe i should get larger duct, similar to the front of the house.. and use the 8x12 to go under the crawl space to supply the rooms upstairs that are colder then the rest of the house.

right now i have 2 6 inch hot air and one cold air in a room 18x20 with 10 ft ceiling and a large window and sliding door.
if i had the 8x12 under the crawl space, i could have 4 -hot air ..

what is a warm air start collar used for, it looks like what we have on our cold air return, i was told it was to help with vibration noise.

beenthere 03-08-2013 03:48 PM

You probably have a flexible duct connector on your return.

Its a starting duct that is bigger at the plenum end the trunk line end. EG: 12X16 at plenum transitioning down to 8X12.

rick31797 03-08-2013 05:08 PM

Duct work
what if i do this, the duct-work on the back side that i am not getting enough heat is 8x12
on the front it is 16x8.. if i use 16x8 on the back also, then i would tie into the 16x8 with 8x12 and run it 20 ft under the crawl space with several round pipe off it.
here is a picture of the 8x12 on the back, you can see how it is conected,
the other picture is what i have on the cold air return that i thought was for vibration

beenthere 03-08-2013 05:20 PM

Thats just a flex connector on the return, it is to prevent vibration noise.

You would need to run the 16X8 into the crawlspace, then afte it supplies 2 of the branches you could reduce it.

rick31797 03-08-2013 05:31 PM

Duct work
I think i am getting what you are saying , i will draw a picture tonight, what i think you mean, too show you..

rick31797 03-08-2013 06:05 PM

Duct work
This is what i think you mean , hope its clear, i didnt put the length of each duct size. would this matter.

Patrick Eubanks 03-08-2013 07:08 PM

Just go get some round balancing dampers. Your making this way too hard.

beenthere 03-09-2013 03:33 AM


Originally Posted by rick31797 (Post 1132767)
This is what i think you mean , hope its clear, i didnt put the length of each duct size. would this matter.

Thats basically what I mean.

16X8 is barely enough for 700 CFM. How big is your furnace(in BTUs).

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