Help me plan new duct routes!


Old 03-14-18, 07:52 AM
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Join Date: Mar 2018
Location: USA
Posts: 3
Help me plan new duct routes!

OK, so whoever built my house was on crack. It's really neat and I love it, but it has a lot of vaulted ceilings and little alcoves and it's just generally insane. It's a 2 story house, and most of the entire system and ducting resides in the attic above 2 upstairs bedrooms and the upstairs hallway bathroom.

Whoever installed the AC/Heating system picked a stupid location for the Coil/Furnace (I think at least), and did not know how to run ductwork for the life of them. The ducts are way too long in some areas, make multiple u-turns, are weird sizes, all leading to poor airflow.

There are only 3 drops from the upstairs attic leading to the downstairs rooms. (I have them labeled 'DS Supply Trunk', and are colored Yellow.) So ran from the plenum, down about 10 feet through the upstairs bedroom/bathroom walls, then deployed through furdowns downstairs. All the drops are undersized, and I can see them crushed in the walls, so they are pretty much useless

A few weeks ago, I went up in the attic and at least straightened what I could, and strapped it all up (It was all just laying draped everywhere) and it helped airflow considerably, but I saw how much better it could have been designed. So, I broke out my chart making software and went to town. I have the ductwork squared off, but it'll obviously be straighter in real life. It's not exactly to scale, but it's close enough.

I have included a Current Upstairs and Downstairs. I'm looking for opinions on my Future plans. I'll post a mock-up of an idea that I think will be a lot better, but I want to maximize airflow (obviously).

So, feel free to offer tips and pointers on how best to do this!

Here's the Attic/Upstairs
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Here's the Downstairs
Name:  Downstairs Current.jpg
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Also, when I attach the images, they get smaller, but it looks like you can 'Right Click>Open Image in New Tab'
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Old 03-14-18, 08:57 AM
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Join Date: Mar 2018
Location: USA
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OK here's potential future plans for downstairs. The furdowns are vastly too big, and can be trimmed back exponentially. I'll have hard ducting in them to maximize airflow. I have a supply to the garage, too. It's right below the master bedroom, so keeping it even slightly stabilized should help the temps in there too.
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Old 03-14-18, 09:14 AM
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Join Date: Mar 2018
Location: USA
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OK I have 3 versions of the Upstairs Future. My biggest concern is getting adequate airflow to downstairs, and the master bed/bath.
Note how I now have ducting coming from the far left end of the main plenum, so air can flow right into it and not have to divert to a side duct. (I think that enough will divert, however, to get the areas right around it, as they are short runs.)
Also note how the lines for the secondary bedrooms aren't so back and forth.

And again, the ducting in real life will be more straightforward; I have it squared off for easy viewing.

1] Uses squared secondary plenums, much like how it is now. They are just better situated.
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2] Uses a raised triangular plenum at the main break. The main duct goes in the bottom and is split 3 ways: downstairs1, downstairs2, and master bed/bath. I have a few wyes in place on the master side of the house.
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3] Uses nothing but wyes; no secondary plenums. I believe this will be the most efficient method, but also the most expensive. (Large Wyes are EXPENSIVE. I may use triangle ductboard splitters instead, and cordon off the interior corners as I'm assembling them to maximize airflow.
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