Duct sizes

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Old 01-19-04, 08:17 PM
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Question Duct sizes

I am in the planning stages of remodeling my basement.
I want to change the duct system to create more head room.

Currently there is one 8" by 8" duct running the length of the house with a total of 6 5" diameter ducts branching off of it within the section I need to modify.

I noticed at the Home Depot a low profile duct that was either 4" by 16" or 4" by 12" Both of the 8x8 and 4x16 size ducts have 64 inchs worth of room for air to flow though
However I recall reading something about air friction making the lower profile one less effective. Is this something even worth worrying about?
Also if it is only a 4X12 would the smaller size mean that this end of the house would get less heat then it is supposed to?

I'm not sure that I explained that as well as I could but I am not sure what else to add.
 
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Old 01-20-04, 04:31 AM
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I'm kinda having a brain freeze right now but 8"X8" seems small for 6-5" runs. Those ducts you saw at HD are for running a supply up a wall.
 
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Old 01-20-04, 05:59 AM
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Thumbs down Duct size

Boy some one looked at the book here for sure . But didnt put any thing in for the so called pot.

5" pipe =60cfm so 6 runs X 60= 360cfm. A 8X8 duct 300cfm . so your short to start with and need more duct.

First I would not run 5" pipe would have used 6". Would have made the duct 8"X14" to feed the 6 -- 6" round pipe.

That poor furnace sure has to work hard to heat that home ED
 
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Old 01-20-04, 07:41 AM
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There should be a maximum of 5 5" takeoffs from that 8X8 duct so it is already overblown.

Don't use the 3 1/4 X 12 wall stack as trunk. There is no way to make a takeoff and it will turn into Frankensteins monster. As Ed has pointed out, you could get a sheet metal shop to fabricate a duct that will work. I would also suggest the 6" runs. If you were to have a duct made to accomodate 5 6" runs it would need to be about 6X16 inches rectangular.
 
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Old 01-20-04, 09:13 PM
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Size updates

Just a few more details to give.
I actually made a mistake, The duct starts as a 12X8 with 3 5" runs from it, there is a run where the 12X8 reduces to 8X8 and then 2 more runs after that.

With this current setup has never been a problem heating the home. However 2 of the runs (1 in the 8X8 and 1 in the 8X12) were to the basement and were closed most of the time.
Also there is another duct running the other way from the furnace to a couple other rooms in the house.

As far as changing the 5" pipes to 6" its not going to happen because all of the pipes are already there and I dont want to upgrade all of them.

If I do use a couple 3 1/4" X 12" pipes running side by side how many 5" vents would be able to run off of each, attaching is not a problem because all the vents would attact on the 12" side. I know using this is not advised but I really need to save the head room as the vents are going to be running right down the main hall way.
 
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Old 01-21-04, 06:40 AM
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That 3 1/4X12 is just what we call a wall stack and feed it with a 6" pipe thats a 100 cfm

A 5" pipe is 60 cfm It just dont work out for you.



ED
 
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Old 01-22-04, 09:07 AM
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Stupid question

I think I already know theanswer to this but I am going to ask anyways.
Right now the current 8X8 vent is suspended about an inch below the floor joists. I know this is so that the vent doesn't heat up the wood and start a fire right.

How big of a deal is it if I get rid of this gap and move the vent up against the floor joists? If I gained an extra inch it would be very close to my beam running across the basement and I could live with that.

The other option I have is to run side by side a 5" round vent from the utility room to each of the 6 registers in place, this would probably fix my head room problem.
 
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Old 01-22-04, 09:50 AM
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Id say check for code there. In some places you can put the heat duck to the joist and others you need that 1" down. Check it out.
ED
 
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