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Discussion Starter #1
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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Discussion Starter #2
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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Discussion Starter #3
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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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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Discussion Starter #5
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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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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Discussion Starter #7
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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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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Discussion Starter #9
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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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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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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Discussion Starter #12
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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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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Quote:
Originally Posted by dc_pilgrim /forum/post/0


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?
 

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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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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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Discussion Starter #17
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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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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Quote:
Originally Posted by dc_pilgrim /forum/post/0


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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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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