# Planning on New duct work..any feedback...



## kilosos2 (Oct 14, 2010)

Wussup guys

I am planning to redo some of my duct work for 5 reasons. 
-Condensation on ducts connection
-Possible undersized duct work as indicated by loud air handler when on 2nd stage
-More Airflow overall
-Possible smaller plenum then should be and a new, bigger maybe needed
-increase some pressure to my family room downstairs which is furtherest from air handler

My air handler is a York 4 ton Mv16cn21H and Condenser Czh04811B with 2 stage compressor with Honeywell IAQ tstat. I currently have the cfm on 1350 high and 860 low because the noise is annoying when the unit runs full speed. I should be 1600 cfm. I am also thinking of putting it on 1700 cfm after I do the duct work.

I am going to break down my layout of my ducts and what I want to do and you guys can give me some feedback.

Plenum starts off the width of the air handler 21" x 21" then it transition to my old plenum which is 16" width by 21" length. The transition is about 10" inches.

As the plenum starts to go up toward the attic maybe 1 ft up, the interior wall on left side of the air handler has a 15"x12" rectangular duct enclosed behind the interior wall. That duct runs down to my first floor and it then connects to all the vents downstairs which are inside the ceiling.

As the plenum goes up to the attic it has 2 main flex duct trunklines . I don't know the exact sizes but either they are 10" or 12" ducts. I measured the duct all around and it came out about, I think if I remember correctly 42".. I guess you call that the diameter of it? lol I don't remember my geometry so well. The trunklines run each about 12 ft.

At each end of the trunkline there is a triangle shape mixer box measured 20x20x16 and 15" deep. On one triangle box I have these flexducts hooked up
1- Main trunk line 10" or 12"
1- 4 inch flexduct that goes to bathroom
1- 6" duct to one bedroom
1- 6" duct to another bedroom
Those two - 6" ducts lol seems to be connected on one side of the triangle box and it seems like they are sharing the connection. 


The other Triangle box has the following ducts hooked up.
1- Main trunk line 10" or 12"
1- 4 inch flexduct that goes to bathroom
1- 4 inch flexduct that goes to walk-in closet
1- 8 inch flexduct for the master room

Now other then that there is one 6" flex duct hooked up directly to my plenum that was added to the master room when I had the new system installed.

Also there is another room next to master room and it has a 6" duct also but that one feeds off the main trunkline that runs to master room. Its weird because the main trunk line doesn't hook up to a triangle box first and then give the 6" duct feed to that room. But instead there is a point where the maintrunk line makes a 90' turn and at that turn there is a junction formed and the 6" duct gets a feed from there and then the main trunkline continues to the triangle mixer box. I have attached 2 layouts for you guys to see all that I have described.

Ok my questions now

1. Is it worth it for me to make a new plenum that sizes with the width of the air handler and will run up to attic 21" x 21 " ? My current plenum also has some mold forming due to the condensation problem, so I kinda of have more reason to rip out the old plenum and make a new one.


2. When I make the new trunklines I am going to have my contractor use R6 1 1/2" ductboards but how should I have him size them? Is 10x8 rectangular duct good size trunk lines? I was told to use the ductboards as they are good in dealing with the noise issue I have. (I am planning to use the ductboards for both plenum and the trunklines) I can also tell you this I did do a heating and cooling load with Hvac- cal 4.0 and it said I need about 900 cfm downstairs and 700 cfm upstairs. I am glad I got that 15x12 duct running downstairs as that probably sends down plenty of air. I just may have to check when that 15x12 duct reaches downstairs how does it connect to the ducts as some vent's pressure are not that strong. Especially my family room the airflow pressure is low there. I am planning to cut a small portion of my ceiling where that 15x12 duct comes down to the first floor so I can see how that 15x12 duct connects the other ducts. I hope there is no triangle boxes there too! I will probably let you guys know what is there after I cut the ceiling.


3. What other feedback you guys have for me? Do you guys think changing my ductwork will help with the noise problem I have?? Can you guys tell from my current ductwork sizes if the ductwork is undersized for the unit? I understand about the condensation problem I have and that they need to be sealed up. I already have RCD mastic on hand to do that but I will do it after the new ducts are up. I also believe this may help give me much better airflow overall.



Check out my attachment and let me know what everybody thinks and if this is a good idea. The pdf file named ductworks is how my duct work is in my attic.


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## beenthere (Oct 11, 2008)

You have about enough supply flex for 500 CFM to move quietly.

What size is your return.


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## kilosos2 (Oct 14, 2010)

The air handler has a grilled closet door that is sized 7 ft x 2 ft wide. I also installed 2 additional return grills both sized 16x16. One grill is on one of the interior wall that faces my hall way and one grill is interior wall behind the air handler and that is above my stairs. Check pics.


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## kilosos2 (Oct 14, 2010)

beenthere said:


> You have about enough supply flex for 500 CFM to move quietly.
> 
> What size is your return.


So I don't need to increase any of my ductwork?


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## beenthere (Oct 11, 2008)

All of your supply runs for the second floor should be larger. And you should get rid of those restrictive pie wedges.

I'd run a duct board trunk line/lines and get rid of the 10 and 12" flex lines, and run all of the supplies off of a duct board trunk line.


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## kilosos2 (Oct 14, 2010)

Ok I will get rid of the flex trunklines and the triangle boxes. I will get my contractor to make me new ductboard trunklines. What about the plenum? Is it sized ok? If I don't have to remove the plenum then I will treat the mold issue ( bleach and water) and mastic the whole plenum up. I found this website 

http://www.hamiltonhomeproducts.com/images/ductwork/DuctChart.gif

Should I base my trunkline sizes with this chart? I figure I can add up the cfm needed on each trunkline and make the correct size. I attached pic of my cfm report from hvac cal.


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## beenthere (Oct 11, 2008)

The plenum size is fine. Up to you if you want to treat it or replace it.

16X21 trunk line after plenum is fine.


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## kilosos2 (Oct 14, 2010)

Ok awesome! :thumbsup:

I have been researching online for last few months and I have gone through a few contractors and no one would give me a straight forward answer! Thanks beenthere for your help! I greatly appreciate it!


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## kilosos2 (Oct 14, 2010)

*My first floor layout.*

Hey Beenthere, I have a few more questions.

I cut open 2 area's in my first floor's ceiling to see how the ducts layout. I first cut open a hole in my family room. I found that the family room has one maybe 8" or 10" duct running into the family room and then it attaches to one of the triangle mixer box. From the Triangle mixer box it spider's three ducts into the family room which also has the kitchen in it. The three ducts are a 8", 6" , and a 4" duct. 

So then I went and checked the main duct that is sized 15x12 that comes from the plenum upstairs. As you have seen in my first post pictures I showed a diagram of rectangular duct that runs from plenum to downstairs. So I cut that and surprise , surprise...as you can see in the picture. How poor work is done when they make modern homes. Anyways as you can see the choke of that duct between the 2x4's. All the pictures are of duct "C" run and also how it is choked. The other ducts I couldn't get clear pictures of them but the diagram shows how they are laid out.

That duct which I labeled "C" in my diagram is the one that runs to my family room. The airflow is poor quality and not alot of pressure. I wanted to do this and I wanted to know if it's a good idea. I want to connect where duct "C" is to where duct "A" position. Duct "A" airflow is very good and it is the duct in my living room. Then I want to connect duct "A" to duct "B" position. Duct "B" is also fair to actually poor airflow. And then duct "B" to duct "C" position. 

I believe if I connect it like this at least where I have the poor airflow the ducts will have straight duct runs without any bends. Now I don't know if your thinking If it is better to extend the 15x12 rectangular with ductboards. Maybe form a Tee shape distribution? I am open to all idea's. I also know the triangle mixer box in the family room need to go as it maybe adding to constricting the airflow. If I remove the triangle mixer box and maybe add a ductboard box there but the duct "C" still connects to it, will that be ok? OR is it better to have a rectangular ductboard supply run all the way to the family room and the each supply connect to them? I don't know of what extend the ductboard extension I can do as I don't know where all the 2x4's are located. But since I will be making the changes. I will be cutting like a 5ft x 5 ft area of the ceiling to reach all of the ducts so I should be able to see everything and then make the adjustment with my contractor. Let me know what you think. I am also thinking of adding dampers so I can balance the airflow after I do all the changes to the ductwork including the one's in the attic.


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## beenthere (Oct 11, 2008)

LOL... I had to read your post 3 times. To make sure i wasn't confusing C, A, and B.

Yes. your thinking is on target. Double check the size of that C duct. Even a 10" will struggle to supply enough air to a 8, a 6, and then a 4" duct. if there isn't enough space to run a 12" without crushing it. then the 10" will still provide more air then what you have had, after you relocate its position on the 15X12 duct.


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## kilosos2 (Oct 14, 2010)

Ok cool. I will keep you posted on the outcome. Ya I proofed read my post 5 times to make sure everything was making sense! LOLL. So the triangle mixer boxes I should just leave alone? ( especially the mixer box in family room?) . If I don't have to mess with it, that will be one lesser place to cut and patch. :thumbsup: 

thanks again for the help
-kilosos2


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## kilosos2 (Oct 14, 2010)

I needed some info on dampers. I am getting closer to redoing my ductwork. I am planning actually to remove my old plenum and install a new one. I am also planning to move up the 15x12 rectangular duct (that runs to my downstair) to the top of the plenum where it is in the attic.

In the attic I will (my contractor lol doesnt want the job..im doin this alone now) install the new trunk lines and also I want to put there dampers on each trunk line before the take off from the plenum.

My question is can I put there motorized dampers that I can control with some tstat or some other device so that when I want to adjust my dampers I don't have to keep goin up in the attic to adjust them manually. Also I can then use the damper controls to balance the whole system and maybe setup certain zoning in my home. 

And if it is possible can you guys give me some names of devices I can use for controlling the dampers? Something that will work and also not break the bank. I want the controls to be independent of my tstat which I have a honeywell iaq. I will have 3 zones because I will have 3 trunklines. I figured to put the dampers at the take off of the supply lines will be the easy way to install them. 

One more question about trunklines....what is the standard for when you attach the flex to the ductboard trunklines ..how far apart each flex supply should be from each other to maintain good airflow and pressure. I also read as the trunkline connects with each flex one should make the trunkline slightly smaller in size to maintain the pressure of the airflow? Is that true?

thanks

-kilosos2


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## beenthere (Oct 11, 2008)

Only need to reduce it if its long. Your trunk line isn't long enough to need to be reduced.

Dampers in each supply are a good thing. however. Motorized dampers are cheap, if your putting them in each supply.


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## kilosos2 (Oct 14, 2010)

beenthere said:


> Only need to reduce it if its long. Your trunk line isn't long enough to need to be reduced.
> 
> Dampers in each supply are a good thing. however. Motorized dampers are cheap, if your putting them in each supply.


You mean they aren't cheap. May not be worth it uh? Ya I saw some of the prices...they are up there. I guess it'll go manual...lol I will only probably need to adjust them to balance.


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## beenthere (Oct 11, 2008)

kilosos2 said:


> You mean they aren't cheap. May not be worth it uh? Ya I saw some of the prices...they are up there. I guess it'll go manual...lol I will only probably need to adjust them to balance.



LOL... Ya, I meant not cheap.

Once balanced. you shouldn't need to adjust then again.


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## kilosos2 (Oct 14, 2010)

thanks again beenthere


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## kilosos2 (Oct 14, 2010)

Hey Beenthere and DIY community.

I made some changes this past weekend on the ductwork downstairs. After I started opening some of the ceiling I really saw what was going on with my ductwork. LOL I had one 6" duct off the plenum that feed a distribution box and split into a 8" and 6" . No wonder I had crappy air pressure from those vents. Anyways I fixed it by making it a 8" duct from plenum feeding into a 8x6x6 wye. I insulated the wye also. I placed dampers also on the 8" duct although I didn't need to balance much. The other 6" duct run I just made it feed into a new 8x8 drop box with a 3 way vent. That 6" also has a damper installed at the start off collar. Everything came out very nice. 

Anyways I wanted to ask beenthere there is one 10" duct that makes a run into family room. I first thought that 10" was being cramped by 2x4( as I originally post about it here on diychatroom) but it is not and it makes a nice clear run without much sag and maybe just 2 turns. The 10" connects into a triangle distribution box and then it feeds the a 4" , 6" and 8". Is it a good idea to make a ductboard trunkline in replacement of the triangle distribution box? After I made the ductwork changes this past weekend my family rooms air pressure also increased. The 8" has good pressure, the 6" is ok but kinda low and the 4" is crappy still. I was wondering if getting rid of the triangle distribution box would help. I also think the ducts need to be sealed with mastic. Do you think it will be a good idea?


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## beenthere (Oct 11, 2008)

It won't hurt. Those triangle wedges are crappy for air flow. They're very turbulent inside and the air doesn't get forced out the way some people say it does. Just too much turbulence inside of them.

Also fix any sags you can. How long is the 10" again.


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## kilosos2 (Oct 14, 2010)

Ok I will remove that triangle box and make a 10x8 ductboard trunkline maybe about 4 ft long.k I will also just seal up the ducts. The 10" duct run is about 20 ft I think more or less. I can also just make ductboard trunkline from the plenum into the family room but that is going to require cutting into more ceiling space!! loll


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## beenthere (Oct 11, 2008)

You would want a 12X8 duct. A 10X8 won't carry as much air as a 10" round.


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## kilosos2 (Oct 14, 2010)

Hey Beenthere

I have been pondering about what to do with replacing the triangle box. I cant make a ductboard trunkline to fit on the plenum.. it seems to be too much labor/cost/cutting and finishing involved. loll The 10" duct isn't leaking at least from the plenum, I still havent opened that area in the family room to check the triangle box to see if its leaking or not. I will be cutting into it on tuesday. What do you think about using a tri wye? I found some on this website

http://bestbuyheatingandairconditioning.com/Merchant2/merchant.mvc?

I made a wye for that 8" that split 8x6x6 and it came out nice.
What combination of the tri wye would have good air flow and air pressure with a 10" duct as supply. What I was thinking of do is placing 3 ducts with 2 having 3 way vents. The 3 way will kinda of shoot off everywhere. And 1 ( a 8") duct is going to be on the wall adjacent to the vaulted ceiling (12-13 ft high ceiling) shooting down into the family area. I am going to post pics later of how the ceiling looks to give you a idea. I will also place a damper on the 10" startoff collar. Someone also told me to install at the 10" take off a scoop damper for more air pressure. I am thinking a 10x8x5x5 tri wye or a 10x7x5x5. What do you think?


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## beenthere (Oct 11, 2008)

I would probably use something more like a 10X8X6X6. And use a damper in the 8 inch to help put more air to the 6" if needed.


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## kilosos2 (Oct 14, 2010)

Ok I am going to try that configuration. I'll let u know how it pans out. And should I try that scoop damper or no?


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## kilosos2 (Oct 14, 2010)

I just ordered a 10x8x6x6 tri wye lol...ouch its $65 with shipping. Let see how this works out.


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## Earnie (Jan 24, 2008)

This is what Lxxxs home improvement store sells on the shelf. I have ordered duct components through the store.

http://www.standexadp.com/catsearch.php


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## beenthere (Oct 11, 2008)

kilosos2 said:


> Ok I am going to try that configuration. I'll let u know how it pans out. And should I try that scoop damper or no?


A scoop definitely won't hurt.


And those Tee's aren't cheap, but worth the money for the air flow improvement you get.


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## kilosos2 (Oct 14, 2010)

Thanks for the website Earie. They got a big selection. Ya beenthere it is worth it. I hope I receive everything by friday so I can try on the weekend. Thanks again for your guys help and guide. I really appreciate it big time.:thumbup:


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## Earnie (Jan 24, 2008)

Thanks for your link too. You may have saved me some money. 

I'll be changing out four 90 degree branches off a main trunk. Instead of using four single Wyes, looks like I can use two Tri-Wyes.


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## kilosos2 (Oct 14, 2010)

LOLL Awesome! Well good luck with that!!!!!


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