DIY duct work

788 Views 5 Replies 3 Participants Last post by EGrant23, Mar 30, 2020

EGrant23

Discussion Starter · Mar 30, 2020

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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EGrant23

Discussion Starter · #4 · Mar 30, 2020

beenthere said:
Oval duct does not flow the same amount of air as the same size round duct. EG: 7" oval only flows as much air as a 6" round duct.

Establish how much air a room needs, then you can establish how much air it needs.

The basement will often not be as warm as the upper level. If you don't zone it.

So, would you recommend 7" oval for the returns through the wall then? I am OK with the basement not being as warm as the upper level as that's pretty typical here in MN. I do want it to be comfortable though. It's pretty standard around here to have 1 supply/1 return in each bedroom and 2-3 in living rooms, etc depending on the size. I just figured I would be safe copying what the builder did size wise. Maybe not though?

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EGrant23

Discussion Starter · #6 · Mar 30, 2020

user_12345a said:
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.

Unfortunately code here requires that ducts be used in interior walls. This changed a handful of years ago.

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