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Old 03-01-2009, 06:12 PM   #1
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duct trunk diy site


I have a two story home built in 1945. The house is 24'x24'. The current trunk line in the basement starts off very large and then gets progressively smaller on the supply and return lines.

I'm planning to have the furnace replaced with a 92% or higher efficient furnace.

I would like to make the trunk smaller so that I can get more headroom for a basement washroom. I figure this would be a good DIY project. Is there a good site that I can learn about duct design?

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Old 03-01-2009, 07:41 PM   #2
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duct trunk diy site


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Originally Posted by unixb0y View Post
I have a two story home built in 1945. The house is 24'x24'. The current trunk line in the basement starts off very large and then gets progressively smaller on the supply and return lines.

I'm planning to have the furnace replaced with a 92% or higher efficient furnace.

I would like to make the trunk smaller so that I can get more headroom for a basement washroom. I figure this would be a good DIY project. Is there a good site that I can learn about duct design?
http://ateam.lbl.gov/Design-Guide/DG...worksizing.htm

The requirements of your high eff. furnace might conflict with reducing the duct size.

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Old 03-01-2009, 08:26 PM   #3
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duct trunk diy site


The first thing you need to know is the furnace size. If sized properly not off the old one there may be a chance of making the duct smaller. If adding A/C you may not be able to reduce. Size equipment first.
See more info on furnace sizing
www.comfort-calc.net/home-page.html
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Old 03-01-2009, 08:34 PM   #4
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duct trunk diy site


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Originally Posted by unixb0y View Post
I have a two story home built in 1945. The house is 24'x24'. The current trunk line in the basement starts off very large and then gets progressively smaller on the supply and return lines.

I'm planning to have the furnace replaced with a 92% or higher efficient furnace.

I would like to make the trunk smaller so that I can get more headroom for a basement washroom. I figure this would be a good DIY project. Is there a good site that I can learn about duct design?


Your duct size will have to be matched to the CFM'S of the blower @ ???? static pressure.If you decrease the duct size. You may get some air noise in the house & may not get enough air flow across the A/C coil or heat exchanger

Last edited by kenmac; 03-01-2009 at 08:40 PM.
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Old 03-02-2009, 05:37 AM   #5
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duct trunk diy site


If your old furnace was an 80,000 BTU output, it probably moved about 925CFM.
A new 60,000 BTU output furnace will need to move the same 925 CFM to stay within its safe temp rise ratings.
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