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DIY duct work

787 Views 5 Replies 3 Participants Last post by  EGrant23
Greetings, again! It looks like there is a boatload of information and knowledge on this forum so while I'm here, I'd like to run a few other questions by everyone. I am preparing to do the ductwork for the basement I am finishing. I followed the builders plans. Two smaller 11'x11' bedrooms, a 14'x24' living room, a bathroom, laundry area, and a small storage closet. I've gotten some advice from my neighbors who have recently finished their basement. This home was built 2 years ago and the duct work seems pretty straight forward. It's a split level in Minnesota with the basement 1/2 underground and insulated well. The main trunk runs the length of the basement splitting the basement in half while the return trunk runs about 1/2 the length of the basement. I'm going to run ceiling supply and low wall returns. 1 of each in the bedrooms and 2 of each in the living area. The builder had already ran a supply in the basement to one of the future bedrooms so I will be copying that with the other 3. 6" leading to a 10"x4" for the 4 supplies. I will be using oval duct for the returns. My questions are these: The ceiling is getting a little crowded already, I was planning on using flex duct for the two bedroom returns but it'll approximately be 15' of straight-ish run. Is this acceptable? Also, I've read varying opinions on tape and/or mastic. If I could get away with just using tape, I certainly would but I also want to do the job right so if both are recommended, that's what I'm going to do. Thank you so much!
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Flex ducts have to be sized larger than metal to get the same airflow.

There's a danger of starving other rooms in the house if you add too much supply to the basement. The trunks have to be sized for the branches connected, you can't just add as many branches off an existing trunk as you'd like.

Basements have relatively low heat loss.

With ceiling vents, best to keep the velocity high so the warm air gets forced towards the floor and mixes well. If velocity is too low, warm air just rises to the ceiling.

I would use 3x10 registers even with a 6" pipe feeding to keep the velocity up.
usually don't run return ducts through interior walls, the wall cavity itself is used and joists are panned off to create a path back to the return trunk.

This style return system is a bit leaky but it does work.
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