Duct Size

[dhslc]

Well I'm back again kicking arround more ideas. The issue that I am trying address is that the house I am purchasing has the furnace in the center of the house and the duct work running across the floor joist is large enough that it makes the ceiling too low to get from one side of the basement to the other. I am looking for ideas on how to reduct the basement without loosing ceiling height. How do I figure out how big my ducts need to be, and are there any helpful hints that anyone has to offer?

Thanks

[coolwhip]

Your looking at it all wrong. Its not that the duct is too big..its because the floor is too high.

[jrbenny]

9' walls.

Without them, you get low ducts. Period.

[jeffshvac]

you can always purchase a ductulator and an hvac contractor to reconfigure your duct system. thanks

[coolwhip]

There is only one way to do it. You need to know how much cfm you need in each room and design your duct accordingly useing a .1 friction rate.

[tinner73]

make the duct shorter and wider. you'll need a ductulator and someone who knows how to use it.

[beenthere]

Tear out the ducts, and furnace, and install a boiler.

The copper is alot smaller then duct work.


Ok, how much heigth are you trying to gain.

You might not be able to make your duct as short as you would like.

[dhslc]

There are two sections of the duct where I am trying to gain about 6 inches. The current main ducts are 18"by30". The areas I am trying to raise are at either end of the main duct. As I understand it, I need at least 6" ducts to feed each vent. I was wondering if I could simply cut the main ducts shorter, and break to individual runs earler? I realize that this will unbalance the system some, and that I'll have to control it at the vents. Does this sound like a reasonable solution?

Thanks

[deejoe]

wow! ...30 x 18 mains.
why not just close off the other 40 rooms and live in a small part of the basement

[jeffshvac]

what size furnace do you have down there?that supply trunk is way oversized for a residential application.call in an hvac contractor and have your duct properly sized and reconfigured.

[beenthere]

It may or may not work, as you increase the length of those 6" runs, you may decrease the flow.

Can you take pics of the duct work, and post them. Also the brand an model of your furnace.

[dash]

Originally posted by coolwhip
There is only one way to do it. You need to know how much cfm you need in each room and design your duct accordingly useing a .1 friction rate.

.1 is just a rule of thumb,Have a Manual D( from http://www.acca.org ) ,duct sizing Calculation done to find the correct friction rate.

[dash]

To reduce the 18" to 12",the 30" must increase to 50".


Taking the branch runs off closer to the pleunum,would allow the trunk to be educed,may requie the 6' rounds to be 7 or 8"s.Really need that Manual D calculation.

[jrbenny]

Damn. 18x30. I was envisioning a h/o upset with the standard soffit. Wow. That's some big duct. I'd hit my head on that, and I'm only 5-10.