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Discussion Starter · #1 ·
I'm wondering if I can move this return trunk to the opposite side of the support beam. The video below is a "round trip". If it can't be moved to the other side of the beam, I would want to move it to the wall shown in the background when looking directly at the beam. I think either option would allow a better soffit solution regardless of where I end up on the design front.


I do plan to replace all the rigid ducts with the FlexMaster stuff thanks to Big's oft repeated recommendations across AVS. If I move the return trunk, is there a similar solution? DIY Ductboard?


I've seen folks post that HVAC work is one of the easiest to DIY. Is that really true? I'm going to bring in some HVAC contractors for bids and the resulting general advice, but I was curious how much I could do myself. If I had a helper how long would it take? An afternoon/whole day? How long if I could convince my kid's friend's HVAC pro dad to help?


Any input would be greatly appreciated.


The Trunk Round Trip (bad narration)
 

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I'm not a HVAC guy but I've just done a bunch in my HT build and posted some pics today (see sig). It seems perfectly reasonable to move the return trunk and you can certainly mix and match metal ducts with duct board with flex duct. A couple of things to keep in mind are that you don't want to add restrictions to the flow. The returns that pass through the floor look to have quite a large area. You will be hard pressed to come close to this area with flex ducts because of their shape. It looks as though you would be better off using duct board where you can maximize the area of the joist bay. There are a few techniques for joining duct board to metal ducts. Here is the guide that I learned from:
knauf fabrication instructions


Good luck.
 

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I basically did what you are proposing and is described in my build thread. What I don't get about your set-up is why they didn't run your return trunk between the forced air trunk and the beam. It looks like they tied in a joist space crossover right after where it left your furnace and then ran it on opposite side of the forced air trunk, yet most of the tie ins to the return appear to be coming from the opposite side of the beam
Seems bass ackwards to me, but may be some extenuating circumstances that I can't see in your video.


I'd wager a guess your HVAC estimate will come in at around $1000 give or take. I got quoted $1700 to move my return to opposite side of my beam and then move forced air over to the beam (where the return originally was). I did it myself for around $200 or so but I didn't consider it easy. Lots of measuring, cutting and cussing but it was only me doing the majority of the work. If you do it yourself make sure you have the right tools or it will take forever and you'll regret it for sure. I'd bet you'd spend the better part of a weekend on it.
 

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Discussion Starter · #4 ·

Quote:
Originally Posted by Moggie /forum/post/17001134


I'm not a HVAC guy but I've just done a bunch in my HT build and posted some pics today (see sig).

I have LOVED your build from the start! Very ambitious...


Quote:
Originally Posted by Moggie /forum/post/17001134


It seems perfectly reasonable to move the return trunk and you can certainly mix and match metal ducts with duct board with flex duct. A couple of things to keep in mind are that you don't want to add restrictions to the flow. The returns that pass through the floor look to have quite a large area. You will be hard pressed to come close to this area with flex ducts because of their shape. It looks as though you would be better off using duct board where you can maximize the area of the joist bay. There are a few techniques for joining duct board to metal ducts. Here is the guide that I learned from:
knauf fabrication instructions


Good luck.

So, if I moved the return trunk all the way to the wall (~12ft from current location), fab'ing ductboard box runs above the current romex and speaker cables for each of the returns would give me about 5"x18" internally. I'm not a math wiz but I think you are right that it would be much better flow than the flex duct. My concern is that by adding this additional length to each of the runs and the trunk that it will impact the performance of the entire system.


Thanks for chiming in and that link!
 

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Discussion Starter · #5 ·

Quote:
Originally Posted by fotto /forum/post/17001154


I basically did what you are proposing and is described in my build thread. What I don't get about your set-up is why they didn't run your return trunk between the forced air trunk and the beam. It looks like they tied in a joist space crossover right after where it left your furnace and then ran it on opposite side of the forced air trunk, yet most of the tie ins to the return appear to be coming from the opposite side of the beam
Seems bass ackwards to me, but may be some extenuating circumstances that I can't see in your video.

Well, I'm just going to keep telling myself it's all jacked up because I got such a great deal when it was built. But we all know the truth is some builders are simply trying to maximize profit, at the cost of doing things right. Crazy as it seems, I'd still rather them be in business today (as they are) due to their focus on profitability as opposed to other builders who went belly up for whatever reason.


Quote:
Originally Posted by fotto /forum/post/17001154


I'd wager a guess your HVAC estimate will come in at around $1000 give or take. I got quoted $1700 to move my return to opposite side of my beam and then move forced air over to the beam (where the return originally was). I did it myself for around $200 or so but I didn't consider it easy. Lots of measuring, cutting and cussing but it was only me doing the majority of the work. If you do it yourself make sure you have the right tools or it will take forever and you'll regret it for sure. I'd bet you'd spend the better part of a weekend on it.

I'm willing to pay someone a grand to do it all in a day and be done with it so I can start framing. I went back and re-read your thread and it was clear you thought it was a big PITA. So I guess the question for me is will I be able to keep telling myself "I'm saving a thousand dollars, I'm saving a thousand dollars, I'm saving a thousand dollars" while slicing my hands and cussing....
 

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HVAC quotes are usually quite ridiculous as they don't require very skilled labor and the tools required are minimal (most people usually have hack saws, tin snips, etc.) Materials are relatively cheap.


I only used flex duct. I rerouted 3 lines to run along the sides of the room and moved the return to the wall.


All in all, it probably cost around $150 in materials and a good day's worth of labor to do it right.


I was quote $2100 which was absurd.


The key to good and quiet flow is to keep the volume of the ducting large without restrictions. Bends/turns are good with flex ducting to reduce turbulence.


Just a few thoughts!
 

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Quote:
Originally Posted by Johnsteph10 /forum/post/17006028


HVAC quotes are usually quite ridiculous as they don't require very skilled labor and the tools required are minimal (most people usually have hack saws, tin snips, etc.) Materials are relatively cheap.

I can't possibly agree more...
 

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I also moved my cold air trunk from one side to the other. Yes the edges are sharp but the job is really not that difficult.


The first post in my thread (see signature) shows the before and post 8 shows the after.


As for using flex line, I would consider the comments about restriction to flow. Generally, they use the full space of the joist cavity. Any flex line would be a significant reduction in square inches.


It was a little trickly but I did this without help. A second set of hands would have come in handy just to hold the duct in place while I threw a couple screws in. Not exactly skilled labor, just a second set of hands with a second ladder.


Cordless drill with socket bit that fits those little screws

Extra little screws

Tin snips

You may need extra sheet metal but doubtfull. Generally the new drywall will take the place of much of the sheet metal provided you are drywalling.
 

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First off flex duct should never run more than 6', it is meant as a means to attach your trunk line to your register with no noise transmition. Secondly without knowing where your returns are upstairs there really is no definate answer. It is hard to tell where the return to your furnace is located but you may have to completely reroute that which could be why it is where it is. The key to having a quiet efficiently operating forced air system is to have everything sized right. Forget duct board, just use the existing duct, then you can buy "panning". You block off the end where the return comes down away from the trunk, you then use the panning to span the joist back to the trunk where it gets tied in. You effectivly turn your joists into the duct work. Save time and money on material. The biggest thing then is to figure out the best way back to the furnace return and getting that taken care of. The project would take a while depending on your skills and how many hands you have. If you get the right contracor this should not be a big expense for them either and they may even be able to reuse much of what is there already.
 

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Anyone who thinks their quotes are high keep this in mind. First off the company has to buy material, then someone gets paid to pick the materials up and deliver the material, then the wages of the installers needs to be paid, lets not forget about tax's, insurance, oh yes and some profit for the company. As far as not needing skill to do the job, while it may not be the job requiring the most inteligence there is definately skill involed in installing it correctly and nicely.
 

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Quote:
Originally Posted by Audixium /forum/post/17005949


I have LOVED your build from the start! Very ambitious...





So, if I moved the return trunk all the way to the wall (~12ft from current location), fab'ing ductboard box runs above the current romex and speaker cables for each of the returns would give me about 5"x18" internally. I'm not a math wiz but I think you are right that it would be much better flow than the flex duct. My concern is that by adding this additional length to each of the runs and the trunk that it will impact the performance of the entire system.


Thanks for chiming in and that link!

Glad to know someone is enjoying my build thread!


Back to HVAC ducting:


5x18 = 90 sq/in


By comparison:

6" round flex duct = 28 sq/in

8" = 50 sq/in

10" = 79 sq/in

12" = 113 sq/in


I see that bigbare is stating that flex duct should be no longer than 6' which is not really true. It might be the norm for connections off a metal duct like yours, but my house and just about all other houses I've seen in California use flex duct throughout the entire house from furnace to vent. Anyway I don't think you can get the flow you need without making rectangular ducts in metal or duct board. Rectangular metal ducts are problematic DIY because you need a sheet metal brake. I think you are left with two choices: DIY duct board to connect to the moved metal duct or pay a HVAC professional to construct sheet metal duct extensions.


Cheers.
 

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Just because you see this doen does not mean it is correct. My profession is in the HVAC industry. Flex duct was never meant for ducting a house, unfortunately someone came up with the grand scheme to use it to get jobs done faster and cheap. Doesn't make it right. I can't tell you how many jobs that have had to be redone because someone over used flex duct and it was causing cooling and heating issues within the building which then costs the customer twice to get the job done right.
 

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Discussion Starter · #13 ·
For each return coming into the basement, there is sheet metal across the bottom of the joists. Then, the trunk runs across the basement, and of course under each return for the tie in.


My preferred option is to move the trunk to the far wall. This will introduce two 90 degree turns in the trunk. Then I would extend the current return ducts by just covering the bottom of the joists with sheet metal like they are now.


Given that some of those joist cavities have various power, RG6, and speaker cable running through them is it ok to just close up the joist and make it the duct run?
 

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For code, I'm pretty sure it's OK to have electrical run through a return cavity, but not forced air. I have at least one ran through on our original home build which passed code, and I remember something to that effect when reviewing NEC.


I was thinking moving that return to the wall was the easiest approach and just panning like you said, but with that you have the downside of all of those extended runs being flanking paths for sound (assuming they are within the HT area), since you can't really do much other than duct liner to insulate. Might not be a big deal for you though depending on goals.


I was probably being a bit over dramatic on my negative comments in my build about doing my HVAC. Like RPh Drew, I was a one man show for 90% of what I did, which was pretty frustrating. It's not easy getting an 8' long 8x20" piece of trunk to align with another section's S channels by yourself. Prop one end up, try to get the other end in place, go back to other end to screw into joist, drop screw and can't reach (can't get to floor without whole trunk coming down, yell "help" at the top of your lungs at 11:00 at night to wake up the wife for assistance, get reamed out by very cranky wife. Well, you get the picture.
 

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Will you be drywalling directly on the joists? If so, the drywall will serve the purpose of sealing the cavity and will eliminate the need to sheet metal the bottom of the cavity.


Second (and I am no pro on this so get some real advise from someone who is) if you have wires that enter or exit a cold air return cavity (the joist space in this case) the hole your wires enter or exit through need to be sealed with fire rated caulk.
 

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Discussion Starter · #16 ·

Quote:
Originally Posted by fotto /forum/post/17008121


For code, I'm pretty sure it's OK to have electrical run through a return cavity, but not forced air. I have at least one ran through on our original home build which passed code, and I remember something to that effect when reviewing NEC.

Thanks - I'll confirm, but it just seemed a little odd to me.

Quote:
Originally Posted by fotto /forum/post/17008121


but with that you have the downside of all of those extended runs being flanking paths for sound (assuming they are within the HT area), since you can't really do much other than duct liner to insulate. Might not be a big deal for you though depending on goals.

Hadn't even thought of that! I'd be bringing all those runs to the screenwall. I think that isn't a very good idea, since while watching movies at night I'm trying to avoid:

Quote:
Originally Posted by fotto /forum/post/17008121


wak(ing) up the wife

and then getting...

Quote:
Originally Posted by fotto /forum/post/17008121


reamed out by very cranky wife. Well, you get the picture.

Maybe I should just move it to the other side of the beam...
 

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Quote:
Originally Posted by bigbare /forum/post/17007062


First off flex duct should never run more than 6', it is meant as a means to attach your trunk line to your register with no noise transmition. .

Absolutely not true. There is no length restriction.


Is flex duct cheaper than running rigid ducting? Yes.


As long as you size it appropriately, plan out the run appropriately, and buy quality flex, it is every bit as good.


The key is to not undersize it.
 

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Quote:
Originally Posted by Johnsteph10 /forum/post/17008332


Absolutely not true. There is no length restriction.


Is flex duct cheaper than running rigid ducting? Yes.


As long as you size it appropriately, plan out the run appropriately, and buy quality flex, it is every bit as good.


The key is to not undersize it.

I guess the five years of trainig and 8 years of exerience in the HVAC trade must have all been wrong then . My bad. As for the electrical you'll have to check code on that one, I have seen piping and electrical run through them before however if it is up to code or not you'd have to look or ask an electricial.
 

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As a side note for the OP I highly doubt that you'll get much noise transmition from a return duct.
 
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