How Do You Figure Out What Size Vents/ducts To Put In? - HVAC - DIY Chatroom Home Improvement Forum

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Old 11-13-2010, 09:33 PM   #1
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how do you figure out what size vents/ducts to put in?

I have limited space and bought a 6" flex duct tube and a 10x6 register to see if it would fit where I want it to go. It'll fit just fine. So the question is how much flow do you get from this size duct?
I have NO central air and wanted to at least get the vents in place now that I have the roof mostly off.

Am I looking at this the wrong way? For example, if I use 6" duct through out the house, then if 1 room is twice the size of the others, just have 2 ducts in there.
Or is this more of using baffles/limiters to restrict flow to some to get more to others?


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Old 11-14-2010, 05:21 AM   #2
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A 10X12 bedroom on the north side of the house needs less cooling then a 10X12 on the south side of the house.

A 20 foot long piece of duct moves less air then a 10 long piece of duct.
A 20 foot long piece of duct ran straight moves more air then a 10 long piece of duct with 3 90 turns in it.

A room by room load calc will tell you what size A/C you should have. And tell you how much air each room should get. Which then allows you to size your duct work.

Its worth its 50 bucks.


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