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kilosos2 10-16-2010 10:55 PM

Planning on New duct work..any feedback...
2 Attachment(s)
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.

beenthere 10-16-2010 11:03 PM

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

What size is your return.

kilosos2 10-16-2010 11:20 PM

3 Attachment(s)
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.

kilosos2 10-16-2010 11:21 PM


Originally Posted by beenthere (Post 518165)
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?

beenthere 10-17-2010 04:11 AM

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.

kilosos2 10-17-2010 05:23 AM

2 Attachment(s)
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

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.

beenthere 10-17-2010 06:34 AM

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

16X21 trunk line after plenum is fine.

kilosos2 10-17-2010 05:40 PM

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!

kilosos2 10-28-2010 06:37 PM

My first floor layout.
5 Attachment(s)
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 , 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.

beenthere 10-28-2010 07:10 PM

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.

kilosos2 10-29-2010 07:07 AM

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 11-07-2010 09:27 AM

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 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 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?



beenthere 11-07-2010 10:44 AM

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.

kilosos2 11-07-2010 10:58 AM


Originally Posted by beenthere (Post 530200)
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 I will only probably need to adjust them to balance.

beenthere 11-07-2010 11:02 AM


Originally Posted by kilosos2 (Post 530209)
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 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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