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post #1 of 44 Old 02-06-2007, 06:46 AM - Thread Starter
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Here is the situation. I need to figure out how to get air into my theater. I am working with an HVAC pro, but this sound isolation stuff doesn't sync up. At this point he has asked me to tell him what I want.

We are zoning the system (1 zone per floor, 3 total). There are some beams that have caused problems. To the right of NASTY BEAM 1 - the bays go East- West - on the other side they go North-South - - this has caused LOTS of problems on the retrofit (we moved the furnace from one side of the beam to the other).

Here is where we are now. Some of the final stitching together of the ducts isn't done yet.

  • The HVAC guy plans to run 2 "7's" of flex as supplies into theater. He says we can only run them 14 feet from the last point of tin where they branch off (presumably inbetween the furnace and the theater wall).
  • He says that the supplies will be pretty manageble from a sound isolation perspective since they only share the basement zone
  • The return is on a party line, so would be hard to contain sound
  • Also, there was some reason why I couldn't just run flex to the return (sorry he talks in jargon, its hard to keep things straight) Might have been a capacity or distance issue.
  • He suggested, essentially venting the H.T. into the utility room
  • That struck me as a lousy idea since I am building a staggered stud wall with GG and 2xdrywall, so big vent holes seem bad
  • I know I need a return though . . .
  • He likes to work with flex and tin ducts, I mentioned ductboard to him, he said he didn't like the stuff and doesn't work with it

So how do I hook my return in? Assuming I can get some bends in the supplies (although the 14 feet distance makes it hard to snake into the other room, the return is the tough one. The dotted line in the diagram is a soffit line, and isn't etched in stone.

I seem to remember seeing something about a baffle box in the archives. I tried a search, but might that be an answer?
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post #2 of 44 Old 02-06-2007, 07:09 AM - Thread Starter
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Oh, and the guy was real concerned when I mentioned I was planning to put in halogen sconces. My wife heard that and nixed the halogen sconces, so back to the drawing board for those.
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post #3 of 44 Old 02-06-2007, 07:39 AM - Thread Starter
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This is the thread I was thinking about.

http://archive.avsforum.com/avs-vb/s...e&pagenumber=1

An interesting idea was put forward by Bigmouth, and discussed by BasementBob - Some quotes -

Big
Quote:
I would make a serpentine box sitting on the floor where you have the vent currently exiting the room. Line ALL interior surfaces of the box with either fire resistant egg-crate foam or the rigid fiberglass. The air path should resemble an S curve with no direct sight line from entrance to exit.

Connect the exit to an INSULATED flex duct (not that noisy thing you call a flex duct) and make another couple of bends and connect to the main branch of the return further back away from the other return. Just patch up the hole made for that thing you've got there.

Time to start trying some DIY. You should be able to do all I described for under $200 including tools.

Bob
Quote:
BIGmouthinDC's idea of a "serpentine box" I think is called a 'plenum with baffles'. And that works well. I got a 25db(C) reduction with a 2'x2'x1' one lined with NRC0.85 acoustic ceiling tile (I had some broken pieces from the office laying around at the time). I made it out of a cardboard box. It might have cost me $2 in duct tape, and just as obviously it's not what you should build it out of.

I don't think you'd want to put fire resistant egg-crate or just any rigid fiberglass into them though -- use something that's HVAC rated (little dirt build up to reduce the effectiveness in 3 months, no mold, doesn't flake fiberglass into the air).
e.g. http://www.jm.com/insulation/perfor...0_superduct.pdf

I need to think about this some. Maybe I'll try to draw a picture to work out the particulars. This might have been how my HVAC guy was proposing to vent into the utility room. Jargon is a bear.
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post #4 of 44 Old 02-06-2007, 07:40 AM
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It seems to me like the HVAC guy undersized your furnace to give you a lower price and is trying to make up for it by running a shorter return.
Now, I don't understand his concern about halogen sconces. What did I miss?

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post #5 of 44 Old 02-06-2007, 07:51 AM - Thread Starter
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The halogen is an outlier - beacuse they are hotter than other lights.

You make a good point about the furnace, that I should have stipulated. It *IS UNDERSIZED* - but it isn't his fault. The builder put in an undersized unit, this guy just moved it.
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post #6 of 44 Old 02-06-2007, 07:52 AM
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Halogen put out allot of heat if he is putting fabric on the walls maybe she is worried about fire. A few years ago there was allot of issues with Halogen lamps starting fires.

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post #7 of 44 Old 02-06-2007, 07:58 AM - Thread Starter
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His concern was 300W orso of halogen would further heat the room, thus needing more A/C. Of course they will mostly be dimmed so its probably less of a concern.

Also, my wife's house caught on fire a few years back, so she had been concerned about them for a reason similar to what Don mentioned.
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post #8 of 44 Old 02-06-2007, 12:27 PM
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I hate to tell you but even after zoning......if you have an undersized unit you really have a problem. I would deeply consider upgrading to the correct sized equipment for what you are attempting to heat/cool. Chances are over they years it is going to cost you a considerable amount of money to keep going the way you are.

With tax incentives for higher efficiency units coupled with the added comfort replacing your incorrectly sized units with new, you will likely come out ahead.
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post #9 of 44 Old 02-06-2007, 12:51 PM - Thread Starter
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Interesting point Grisby. I had a couple of HVAC guys in. On said it was undersized after doing some calculations (the one who is doing the work) - the other said it was fine, but didn't really do anything other than glance at it and say "its fine".

The suggestion was to run zones, so that it would run more often, but be more equal to the job in the zones. Its only 2.5 years old, "energy-star" (although aren't they all?) so replacing it seems counter-intuitive. Real tough to swing in the budget right now, also.

Is it the under sized unit that limits its ability to handle longer flex runs for supplies? That is what is killing my ability to run the ducts through the soffit with a turn or two. I am thinking I just run the supply to the front part of the room (not behind the screen), drop into the soffit area for a quick turn or two and back to the furnace. For the return, I am debating a "plenum with baffles" either hooked to the return or dumping into the utility room (maybe with a fan that can run off 12v triggers from the receiver?)
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post #10 of 44 Old 02-06-2007, 12:55 PM
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I've used halogen bulbs and fixtures for ages without event. Unless a halogen unit is defective, fires are usually caused by improper installations, believe me I've seen some shabby work.
An experienced plumber screwed up a faucet that had been back ordered for months - because he liked to figure out puzzles - he totally F'd it up.
We couldn't use our shower for two months.

Note to journeymen: no matter how much you think you know, read the instructions (occasionally, things change).

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post #11 of 44 Old 02-06-2007, 01:30 PM
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You need to find a HVAC guy that will do a full load calculation on your house. This entails measuring the heated/cooled space, taking into account windows, direction of the sun, size of supply/return ducts, etc.

When you have the load calc. numbers then they will be able to tell you if you have the right sized unit. Sometimes zoning can help alleviate the problems with an undersized unit, but more than likely the brain of the zone system will keep calling for heat as each zone makes a request. Meaning that your unit never shuts off AND that no one zone is ever truly comfortable.

What you have now may work okay for your existing space but when you tack on your basement you are going to be putting a solid strain on your system. I know this is painful, I just recently came to the same unfortunate conclusion. I am going to have to add a 1.5 ton unit to supply my lower level. I am a fairly experienced diy-er and found an online source for the equipment, I just have to find someone to come charge it when I get it installed. But even still the equipment is going to run me $2K........at least I will know that I will be comfortable.

Another consideration is.......could you sell your current equipment to help offset the cost of the new? That stuff is always on ebay....

I plan to put all the ducting in and keep finishing the room.....I will add the new HVAC system when I am ready to move into the space......
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post #12 of 44 Old 02-06-2007, 02:07 PM - Thread Starter
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You make a strong case. I'll think about it.

I have to admit, I am probably going to try to come up with a rationalization to "try" the undersized unit and see how it goes. Hopefully I don't cut off the nose to spite my face. Paying a little extra with innefficiencies is appealing in the short run while so much cash is going towards finishing the basement. I'd rather replace it next year. But that's just financing when it comes down to it. . . .
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post #13 of 44 Old 02-06-2007, 06:21 PM - Thread Starter
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Got more feedback by my guy tonight. The 14' thing is a Massachusetts code thing.

On the plus side, we have the "cadilac" of zone dampner controllers going in. We could in theory run a thermostat to practically every room.
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post #14 of 44 Old 02-06-2007, 07:07 PM
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Quote:
Originally Posted by dc_pilgrim View Post

Got more feedback by my guy tonight. The 14' thing is a Massachusetts code thing.


On the plus side, we have the "cadilac" of zone dampner controllers going in. We could in theory run a thermostat to practically every room.


Zone dampers area a good start for an undersized unit. Depending on the number of people in your home and assuming that most people occupy the same spaces you would ideally use occupancy sensors. In the end you can have a very efficient system. The down side is that if you ever have large numbers of people in your home the unit will never keep up. It can cost you almost as much installing all the necessary controls as it would to replace the unit. The question I would have to ask based on the current installation is was the sizing of the duct plenums based on the undersized unit? What happens when you replace the unit with greater capacity is, with the existing plenum, you get greater air velocity and hence more air noise.


Can your zaccommodates accomodate occupancy sensors?

Bruce Haugh, P.Eng.
Mechanical HVAC & Plumbing Designer
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post #15 of 44 Old 02-06-2007, 07:35 PM - Thread Starter
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Thanks Bruce, that's encouraging.

I would assume the plenums are based on the existing unit. We are two adults plus a toddler. Plan to have another one sooner or later. Once a year or so we'll have a very full house when the in-laws arrive.

My guy didn't mention occupancy sensors. The thermostats will be progamable. He showed me the dampner control board and it is a EWC "Ultra Zone". There are 7 dampners to control 3 zones. My ductwork is a bit of a spider web.

Given that the 14 foot limit is a MA code issue, we might be able to push it a bit. I guess national code is 50 feet, but MA never kept up with improvements in the tech. Or at least that is how the difference was explained to me.

I explained to him GG, RSIC and all that. He looked at me like I was nuts. Not all wrong. I am thinking about the baffle plenum to vent into the utility room to address the return. Might consider hooking a fan onto it and trigger it when the receiver turns on.
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post #16 of 44 Old 02-06-2007, 07:51 PM
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Hi Dave,

I've had three diferrent people at my home to take a look at my basement for HVAC and no one has mentioned that a supply can only be up to 14'. In fact im gonna need 3 supply lines that will be approx 18'.

The last guy that came out is a friend of a friend and he suggested doing the baffle plenum to vent into my utility room as well. Tough to remember the Jargon but he said that he would put the opening in the bottom and some sort of insulator up the wall to make the air go up about 48" and this would keep the noise down. Hopefully this will work if not I will be able to somehow run a return later on.
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post #17 of 44 Old 02-06-2007, 07:57 PM - Thread Starter
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The 14' is a limit on flex duct. Metal ducts don't have this limit. I guess once upon a time flex duct was just a bit better than saran wrap, so if you did long runs it wouldn't be effective.

Interesting that the baffle plenum was also a suggestion.
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post #18 of 44 Old 02-06-2007, 08:45 PM
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Next house If I need to run flex duct I'll use something like:

http://www.casco-flex.com/Commercial...Silentflex.htm

Instead I ran down to HD and got that off the shelf brand of flex duct that has a plastic inner sleave. While it was better than the round tin I ripped out I don't think it comes close to the sound control properties of flex duct that is built with an acoustically transparent inner sleave which allows for more absorbtion by the insulation.

There are several products out there using the same concept.
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post #19 of 44 Old 02-06-2007, 08:53 PM
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Quote:
Originally Posted by dc_pilgrim View Post

On the plus side, we have the "cadilac" of zone dampner controllers going in. We could in theory run a thermostat to practically every room.

Can you provide more info on your zone dampner system (brand, ballpark price, etc.)?
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post #20 of 44 Old 02-07-2007, 04:35 AM
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Ask him about whether or not there are limits on using duct board. That'll give you the quietness and potentially allow you to extend the amount of non-tin in the system.

Bryan

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post #21 of 44 Old 02-07-2007, 05:44 AM - Thread Starter
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Quote:
Originally Posted by bpape View Post

Ask him about whether or not there are limits on using duct board. That'll give you the quietness and potentially allow you to extend the amount of non-tin in the system.

Bryan


He is very reluctant to run duct-board because he doesn't like the product. He thinks its prone to mold and generally inferior. I might be able to push him on this one room.

My latest thought is if I can push it a bit on the length, I'd run two supplies of flex through the bays to the opposite side of the room (right of the screenwall), have turn one by the drop, and turn two be coming back to the side of the soffit, then vent into the room. If he won't push past code I might have to put the vents in the ceiling, not the soffit which will only give me one turn.

Then on the left side of the room I make a plenum baffle, use the premium flex that Big linked to above, line the box with linocoustic or similar and run the return from the side of the soffit on the shared wall in to the utility room with a horizontal "S" or two "S's" if I want to go horizontal, then drop into the staggered stud wall and vent into the utility room. Maybe add an in duct fan (as quiet as possible) to facilitate the flow. I expect I may need to DIY the plenum baffle.

My thinking is I get my turns in the supplies, and the long-ish runs might lessen the flanking there. On the return, I might be better off risking a flank to the utility room (under the kitchen) than a flank to return (connected to all the rooms).

But this is the speculation of an amateur. I welcome further advice.
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post #22 of 44 Old 02-07-2007, 05:55 AM - Thread Starter
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Quote:
Originally Posted by snooktarpon View Post

Can you provide more info on your zone dampner system (brand, ballpark price, etc.)?


The dampners themselves (I have 7 for 3 zones) are about 100 apiece at the local supply house. Item # 130074602171 on ebay is exactly what I have being put in the big ducts (the local supply house is about the same price once shipping is factored apparantly). I know that price because I had to add some more in a change order. There will also be a round variation for the flex runs.

The control board is the EWC Ultra Zone. I would assume the "brain" is few to several hundred dollars as a part. The killer has been the labor. They yanked all of my supply ducts in my basement so that they could be broken into separate feeds per floor, sized appropriately. They then had to add additional dampners because the ductwork was running front and back in the house. I think the break down is two dampners each for the basement and bedroom floor. Three for the main floor. My house is about 1000 sq ft per floor (little less in the basement since the concrete walls are thicker.
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post #23 of 44 Old 02-07-2007, 08:07 AM
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On the sconces, if you really want to keep the heat down - go LED. Intital cost is high but almost no heat and VERY efficient and no bulb costs.

Enbryten Sconce

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that is clear, simple, and wrong.


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post #24 of 44 Old 02-07-2007, 10:00 AM
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Quote:
Originally Posted by snooktarpon View Post

Can you provide more info on your zone dampner system (brand, ballpark price, etc.)?

Go to the EWC website here . They have a lot of info including prices. You can also download the .pdf catalog.

Hey DC, can they run round pipe a partial distance then the flex for the last 10 feet or so? That might eliminate the 14' issue. They did that in my house. I have about 8 feet of round pipe then it goes to flex for about another 10-15 feet.

Andy
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post #25 of 44 Old 02-07-2007, 10:55 AM - Thread Starter
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Andy -

The beams and the zoning create some of the problems there. At this point if I can sneak a few extra feet past the 14 with Flex I should be okay. The installer said it will be two feet from the supply to the beam (figure + 1 foot there). The room is 12 feet. So if I go to the far side and back its 2+1+12+(1 or 2) I am around 16-17 feet, as long as there is no lateral distance spent (haven't seen the supply, so not sure how wide it will be, and if it lines up to the bays okay).

Its quite an education this stuff.
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post #26 of 44 Old 02-07-2007, 11:01 AM
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Dave.

If good quality duct board is used and properly cut, assembled, and sealed, there is no reason it's not just as good if not better than flex.

Bryan

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post #27 of 44 Old 02-07-2007, 12:00 PM
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Grigsby or anyone, (Grigsby seems to be quite knowlegable on this subject)

I dont' mean to highjack this thread, if I should start a new one please let me know.

I'm fairly new to this site. I currently have a 90%high efficiency furnace and a 5 ton A/C unit to heat and cool a 3100s.f. home. I have a full basement and will be putting in a dedicated H/T space approx 15 Ft. wide by 22ft. long. Will branching off my existing ductwork to heat and cool the theater with returns effect the efficiency of the furnace or A/C unit? I belive the A/C unit is a 12 or 14 seer unit.

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post #28 of 44 Old 02-07-2007, 08:07 PM
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DC:
What is the square footage of the home and its age?
What size is the furnace BTUH, Eff.(hi or mid), Blower capacity(1200-1600cfm)?
What size is the A/C? What type of Bypass duct are you using?
Could you use the soffit as the return duct and just line it with acousti-duct insulation?
Can you bring the return flex duct through the ceiling beside where the beams meet in the utility room and then tag it in to the return main, doing the S turns (if required incase it still is transfering noise)in the utility room ceiling.
I'd strongly suggest that you upsize the 7" flex to 8" flex for lower branch duct velocity. Look at the link provided by Bigmouth, at 200cfm a 7" has a 600fpm velocity and an 8" has a 500fpm velocity. In residential constant flow design, 600fpm is recommended in the branch ducts, however you are building a quiet theater and your installing a zoning system that will run at higher static pressures. The cost difference will be minimal maybe $15.00 per 25' lenght.

Bill
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post #29 of 44 Old 02-07-2007, 08:27 PM
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When selecting DX components it actually does NOT help to be oversized. You want the compressor to work hard. If you need 6 tons and your options are 5ton or 10 ton...you are better off with a 5 ton unit from a system standpoint and from the comfort standpoint you will be fine for 90% of the time.

Definitely the best option is to install a booted transfer from the theater to the utility room. I do this all the time with lined duct and elbows on both sides...but since you can't have an elbow on the theater side just put 2 elbows on the utility room side. Have to line the duct though....
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post #30 of 44 Old 02-08-2007, 05:47 AM - Thread Starter
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Quote:
Originally Posted by uxbridge View Post

DC:
What is the square footage of the home and its age?

2000 Sqft above grade (1k per floor) a bit less below grade about 900, about 650 Sq finished space. The house is 2 and a half years old.

Quote:


What size is the furnace BTUH, Eff.(hi or mid), Blower capacity(1200-1600cfm)? What size is the A/C?

Not sure. I'll confirm tonight. They call it an "energy star" house - which I assume is primarily driven by the fact that the house and windows are pretty efficient. But the furnace selection may have been a factor. It is forced hot air, gas powered, with air conditioning.

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What type of Bypass duct are you using?

Is this for the zone dampners? The Dampners are motorized, not springs. My HVAC guy was recomending allowing them to go to 80% closed in the "closed" position rather than closing them 100%, using a bypass dampner and feeding the treated air back into the return. He felt it was more efficient, as you aren't cycling the air, and you let a small amount go into the non-called zones. Seemed logical to me. Is that what you were asking?

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Could you use the soffit as the return duct and just line it with acousti-duct insulation?

Don't see why I couldn't. Bryan Pape is helping with accoustics, so I'll need to see if he was planning to use that real estate for treatment. I'll need to run electrical and low-voltage, but that shouldn't be a problem unless code says otherwise.

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Can you bring the return flex duct through the ceiling beside where the beams meet in the utility room and then tag it in to the return main, doing the S turns (if required incase it still is transfering noise)in the utility room ceiling.

There is a lot going on right at that intersection, so there might be a traffic situation. Assuming I am going to run flex, am I correct to assume I could go over the beam closer to the water heater, and then come back with flex (with the desired S turns)?

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I'd strongly suggest that you upsize the 7" flex to 8" flex for lower branch duct velocity. Look at the link provided by Bigmouth, at 200cfm a 7" has a 600fpm velocity and an 8" has a 500fpm velocity. In residential constant flow design, 600fpm is recommended in the branch ducts, however you are building a quiet theater and your installing a zoning system that will run at higher static pressures. The cost difference will be minimal maybe $15.00 per 25' lenght.

Bill

I will request this change. Thanks Bill, this is really helpful.
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