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Earnie 02-10-2010 12:56 PM

Re-Ducting Proposal
2 Attachment(s)
I would appreciate you guys taking a look at my proposed re-duct and point out any issues you may see. I've attached a drawing and I'll explain what is happening. Figured a picture would be easier than trying to explain in writing.

Reasons for the re-duct is to change from R4.2 flex duct to R8 rigid and make room for a humidifier.

Current Configuration: No idea why right duct is 14". Heat Loss/Heat Gain Duct Report calls for 8" @ 200 CFM to supply two bedrooms. The 14" duct is 10 ft long and the last 6 ft is un-used and end capped.

Attachment 17617

Proposal 1: Install TrueSteam humidifier to end of plenum. Will that work? Will the steam still make it into the left and right ducts?

Use existing 14" start collar, add 14" 90 degree elbow, then reduce to 12" to supply 8" and 10" ducts. Or, install 12" start collar and 90 degree elbow.

Proposal 2: Install 12" start collar on end of plenum to supply 8" and 10" ducts. Install TrueSteam humidifier to side of plenum.

Attachment 17618

I'm fairly confident the duct report is providing correct duct size for required CFM/FPM. I'm just not sure of the best location for the humidifier and the least restrictive configuration the 12" supply trunk. Straight 12" off the plenum end or a larger 14" duct with a 90 elbow off the side.

Many thanks.

beenthere 02-10-2010 05:12 PM

Post pics of the set up.
I wouldn't reduce any trunk sizes.

Earnie 02-10-2010 06:27 PM

Hi BT,

What exactly do you want to see in the pictures? Just where the trunks connect to the plenum?

beenthere 02-10-2010 06:31 PM

A pic of the air handler that shows the return and supply connection.
And pics of the duct attachments to the supply plenum.

The Truesteam needs some clearance for its nozzle so it doesn't put steam against the duct work and condensate.

Earnie 02-10-2010 08:51 PM

Here's some info till I can upload the pics, hopefully tomorrow.

Trane XL1200 3 ton Heat Pump w/ variable speed air handler. 1100 CFM.

Three pipes off the supply plenum:

14" rigid 18' long, 4 flex branch ducts; 3 - 8" dia. and 1 - 6" dia.
14" rigid 10' long, 2 flex branch ducts; 1 - 8" dia. and 1 - 6" dia.
10" flex 30' long, 5 flex branch ducts; 2 - 8" dia, 2 - 7" dia. and 1 - 6" dia.

Three pipes to the return plenum:

2 -12" flex ducts 7' long.
1 - 10" flex duct 30' long.

I know I've asked a lot questions in previous posts and some in around-about way, maybe leaving out important info. In my opinion, what I have here is a real mess. I have used a few different HVAC companies in hopes of finding a quality one. No luck yet. That leaves me to research these duct problems and possibly correct them myself, or guide a HVAC company in how to fix them.

The original install had only two supply ducts for the Upstairs. Master Bedroom (22' x 14') had one 8" flex duct with a 4" x 12" floor boot mounted in the ceiling. Loft (17' x 10') had the same, one 8" flex duct in a 4" x 12" floor boot. Both were supplied by a 10" flex duct. The Master Bathroom had NO ducting at all.

After we moved in, I asked a HVAC company about adding a duct to the Master Bath and improving the cooling in the Master BR and Loft. One 6" flex duct was added to the Bath with a 4" x 10" ceiling mounted floor boot. One 7" flex duct added to the Master BR in a 4" x 12" ceiling mounted floor boot. And another 7" flex duct to the Loft, also in a 4" x 12" ceiling mounted floor boot. The original 10" flex duct was used.

All companies that have worked on the system were either Trane or Trane Comfort Specialist certified. Maybe its me; maybe its where I live. Who knows.

I do appreciate the time and information you guys have provided. I now know more about HVAC than I ever thought I would.

beenthere 02-10-2010 11:12 PM

Your duct system is messed up.

Trane CS doesn't mean much. Sent a couple guys to a Trane course or 2. And thats about it.

Earnie 02-11-2010 06:37 AM

Thank you BT. In a strange way that make me feel that what I'm dealing with isn't just me.

Will get those pics uploaded today.


Earnie 02-11-2010 09:32 AM

6 Attachment(s)
This is the right side 14" rigid trunk duct off plenum. Feeds the 8" and 6" bedroom ducts.

Attachment 17632

Other side of 14" bedroom trunk. This is the 8" duct.

Attachment 17633

14" bedroom trunk and upstairs 10" flex trunk connection to supply plenum.

Attachment 17634

Living room, Kitchen, Bath 14" rigid trunk connection to supply plenum.

Attachment 17635

10" flex return air from upstairs 14" x 20" grill.

Attachment 17636

All air return ducts. Nearest is 10" flex from upstairs. Other two are 12" flex from hallway 20" x 25" filter grill. As noted before, the two 12" are squeezed between floor joists making them about 10" x 13".

Attachment 17637

I have a few more but need to delete the uploaded ones since there is a six pic max upload.

beenthere 02-11-2010 10:09 AM

Your supply plenum is a turbulance box. Built too short. And with that 10" coming off the end of the plenum when its as wide as the plenum doesn't help it.

The 10" flex isn't able to carry as much air as its branches want/need.
The 14" are oversized for the branches attached to them.
All branches should be Wye's instead of tee's. But, that can be lived with.

The 10" return looks to be at too hard of a 90 where it attaches to the plenum. That restricts air flow.
Increasing it to a 12" and increasing its return grille would help your system a lot. And allow for the other 12" runs crimping.

Your system static pressure should be checked. Along with the actual CFM of each supply. And then the supply CFM checked to what a load calc says it should be for that branch/supply.

In many ways, it would be easier to start from scratch and redo all the duct work.

How much redo are you looking to do, or invest in?

You can make a second post and put more attachments in it.

Earnie 02-11-2010 01:50 PM


Other than you comment on the supply box being too small, I sort of knew the rest was designed wrong even without any HVAC knowledge. It just looked wrong.

As far as a re-do, that is what I am working towards. What I now know and from what I can see, this system will never be as efficient as it should be. I'll have to live with that as I 'm not going to pay another company to do any duct work. Twice is enough.

I have made one improvement so far for the positive. As mentioned in a previous post, the 10" flex supply and return was going through the roof rafters, directly against the roof decking. They pulled out the insulating batts to install the ducts. Wonder what the heat loss/gain was? I have changed those two flex ducts to 10" rigid and up graded to R8 insulation. I had to sacrifice space in a closet, but now the ducts go from the crawlspace through conditioned space then into the attic. Even without test instruments, I can "feel" the difference in air flow and temperature.

So, after seeing the pictures, which drawing at the beginning of the post is "best"? I'll look into getting a larger supply box.

Earnie 02-11-2010 02:02 PM

Re-Ducting Proposal Part 2
3 Attachment(s)
Here are a few other pictures.

Air Hanlder is sitting on concrete blocks above the dirt floor. Plan to remove those and slide under a 1" - 2" piece of Dow blue foam board.

Attachment 17650

This shows the 10" flex return from the upstairs filter grill. Wonder which is restricting more air, this or the tight bend going into the return box.

Attachment 17651

I thought this was interesting. Start collar with foam seal attached to the outside of the insulation cover vs against the duct itself. You think there's air leakage?

Attachment 17652

I guess those are enough to make my point.

beenthere 02-11-2010 03:56 PM


Proposal 1: Install TrueSteam humidifier to end of plenum. Will that work? Will the steam still make it into the left and right ducts?

Use existing 14" start collar, add 14" 90 degree elbow, then reduce to 12" to supply 8" and 10" ducts. Or, install 12" start collar and 90 degree elbow.

Proposal 2: Install 12" start collar on end of plenum to supply 8" and 10" ducts. Install TrueSteam humidifier to side of plenum.
Use existing 14" duct with a 90 and a Wye/Tee. Increase your current 10" to 14" and run a 14" to the supplies that use to be on the 10". And run a 10" to the supplies that use to be on the 14".

Its like they read a drawing wrong, and ran the wrong size trunk line to those 2.

You don't have enough clearance on your supply plenum to install a Truesteam.

I'd get a longer plenum made. Atleast 18" longer, so you have the clearance to mount it between the air handler and the 14" take off.

Earnie 02-11-2010 05:35 PM

1 Attachment(s)
Somehting like this:

Attachment 17657

If that is what you mean, I have two final concerns and that should be all I need.

beenthere 02-11-2010 05:38 PM

Yes. that way the 10" only has 2 supply branches, and the 14" will provide much more air for the other 5 supplies.

Earnie 02-11-2010 06:21 PM

Ok, last few questions.

Dampers. Are they good or bad? Originally I planned to install one on each trunk off the plenum. So in the final drawing, damper on the left 14", damper on the right 14" after the Wye, and a damper on the 10".

Left 14" rigid pipe. My Heat Loss/Heat Gain and Duct Report says the total CFM need for the rooms is 569 CFM and calls for a 12" rigid pipe. I was planning to reduce it to 12" which would give me a bit more physical room when dealing with the squeezed 10" return. See the middle picture in Part 2 post. Would it be wrong to reduce from 14" to a 12".

Final question, I hope. You suggest a 10" off the 14" Wye to supply air to the two downstairs bedrooms. Report says it can be done with an 8" rigid as total CFM need for the two rooms is 200 CFM. Pipe distance for either room will not be over 15" from the plenum.

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