HVAC Duct Installation

Discussion in 'Studio Construction & Acoustics Forum' started by aaronwiles1, Mar 22, 2004.

  1. aaronwiles1

    aaronwiles1 Guest

    Hello everyone,

    I've been reading through dozens of posts regarding HVAC stuff the last few days, and originally had some questions posted on John Sayers site, but it's been down lately, so here it goes...

    I've been reading Rod's posts about using the Johns Manville Super Duct product http://www.jm.com as well as several other options such as the flexible duct stuff.

    I understand I need to have the ducts turn several 90 degree turns, etc to reduce the travel of sound going through the ducts. I also intend to run separate runs to each room as well as a return from each room. The unit I have is a split unit w/ the air handler in the basement. I also understand I need to knock out another hole in the block foundation to allow a fresh air return w/ a minimum of 10% fresh air since the rooms are hermitically sealed (or soon will be).

    The questions I have are:

    1. Which type of duct work should I use to run through the walls of the control room etc. Should I use flex, or should I use the rigid board?
    2. When running the duct work through the walls, I am assuming they need to NOT touch the walls because of vibration. Correct?
    3. I need a method to hang the duct work to decouple it from the structure of the building.
    4. What type of vent panels would be best for both the send and return to reduce any whistling? I understand the larger the duct work, the slower the air speed.

    Thanks,

    Aaron
  2. timmayock

    timmayock

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    Aaron,
    Rod is on Vacation for 10 days. He is an expert on this stuff. I am more than half way to finishing my superduct system.

    I understand I need to have the ducts turn several 90 degree turns, etc to reduce the travel of sound going through the ducts.

    I believe that with superduct this is not quite so important. but some turns are recommended.

    1. Which type of duct work should I use to run through the walls of the control room etc. Should I use flex, or should I use the rigid board?

    Superduct is probably the best choice. Flex is often restrictive to air flow. If you use flex make every effort to keep the shape. Try not to use thin straping. The sag is bad.

    2. When running the duct work through the walls, I am assuming they need to NOT touch the walls because of vibration. Correct?

    My guess is that this is less of a concern with superduct.


    3. I need a method to hang the duct work to decouple it from the structure of the building.

    My guess is that this is less of a concern with superduct.

    4. What type of vent panels would be best for both the send and return to reduce any whistling? I understand the larger the duct work, the slower the air speed.

    Yes, you are correct the bigger the quieter. I was told that having dampers on the grills will cause noise.



    This is my experience with my recording studio’s HVAC. I want to stress that I am not a duct expert, but I hired a mechanical engineer to design my HVAC system and I highly recommend that.

    I am building my ductwork out of Superduct, a Johns Manville product. Superduct has favorable acoustic properties it helps to keep the sound of the HVAC system to a minimum. I am learning on the job and found a few techniques that I want to pass on. I am a novice “do it yourself” guy and I will mention, I got frustrated with the process, due to a few factors. I can follow directions fairly well, but I could not find much info about how to fabricate this sort of thing. I got advice from Rod Gervias and a few local guys. I had a HVAC guy come over and give me a quote after I was part of the way through building the system myself. He told me my ducts would all fall apart and that he would need to take them apart and redo them I used Home Depot foil tape and regular staples. He wanted $1100 to redo the ducts and finish the job. I got a second opinion. Many of the tin knockers I spoke to don't like this stuff and don't use it. I am way over budget and so I am in the process of finishing the job. I will go back and improve the initial job with the right kind of staples and a hair dryer. Let me say that this may fall into the list of things you want to outsource if you can afford it. I really disliked working with this stuff. It seems worse than fluffy fiberglass in terms of itchyness and it’s effect on your lungs. This part of my project is not going quickly, of course nothing ever does the 1st time and I will be happy to know i used the best material.

    Super duct comes in sheets 10’ x 4’. You need to fabricate the pieces to make up the ducts. Super duct is a rigid fiberglass that has a silver, bendable, outer skin and a black polymer coating on the inside. The polymer keeps the fiberglass from becoming airborne inside the duct. I chose the 1” thick product. The long sides of the ductboard have a 1” inner and outer relief, so a 4’ piece will fit into another of the same size.

    There are machines designed to make this stuff and it may be possible to buy it from a HVAC distributor already made into 4’ sections.
    Much of the mechanical engineers design called for 12” x 3” duct. Here is how I made it.

    I layed out the 4 x 10’ sheet black inner side up.
    I used a 4’ “T” square and chalk to mark the cuts. The basic idea is to remove a 45 degree section of the polymer and the fiberglass. I used 2 kitchen knives to do this. One short knife that I modified with a grinder to dull the point. And 1 large carving knife.

    I marked 3 places for each cut. I made my 1st mark 1” off the end (to make my 1st 45) and then made center marks every 12” and 3”. I made marks 1” from the center as a guide. The center cut is not to go through the skin. This is why you dull the point of the knife. After you have made this cut you bend the board the opposite way 90 degrees. Use the carving knife to make a cut in the 90 degree corner at 45 degrees cutting both sides of the duct at once. Use the chalk marks as a guide. Go slow and take care to not cut the outer skin. This gives you a pretty good corner. Cut through the skin of the 4 cut after you have made the 45.

    Take the newly made piece and fold it into shape. Apply 1 long piece of foil tape along the seam where both end join. I took an old hair dryer and used that on high to heat up the foil and also to rub the tape into the duct. This creates a pretty good bond. On many pieces I used multiple pieces of tape.

    I repeated this several times making all of my 12” x 3” pieces. Then I started to put these together. The 1” relief needs to be taped with foil tape, again I used the hair dryer method.
  3. Thomas W. Bethel

    Thomas W. Bethel

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    I have spent over $10,000 on my air conditioning system. It is very nice now but the major factor in getting all to work correctly was to find a good HVAC contractor. A contractor who would listen to what my needs were and respond in a professional way. I went though a lot of the "whats you needs" people and people who tried to shoehorn an "off the shelf" system into what I needed and wanted. None of them worked. Then I found a good HVAC contractor who is reasonably priced and who does wonderful work. His company has completely changed the way my system works and the efficiency of that system. I too would recommend having a good HVAC contractor do most of the work. They know the local building codes, they know their materials and they now how to work within a budget.

    How do you find a good HVAC contractor? You start by calling them and telling them you have a project that involves moving air quietly and efficiently and that you want them to come over and look over the job before you start construction. If they arrive with a brochure for an all in one system that can be customized to do everything you want it to do be polite and then show them the door. If they come over, listen to what you need and offer suggestions and say they will have to do some research and get back to you maybe you have found someone special. Also ask friends and neighbors who they trust. Also find other studio owners that are satisfied with their HVAC contractors and contact them. Get a second or third opinion from different contractors. If they do not know about things like superduct or they only have one type of grill available then you know they should not be in the running. Most times you will want to find a commercial and residential contractor. They have more equipment choices and they have probably done some very similar jobs to what you are requesting. Tell them your proposed budget up front and if they seem hesitant to do any more bidding ask them what there estimate would be. You may find that in the long run a little more spent up front will make a lot of difference down the road. It certainly was that in our case and the our current HVAC contractor says we could have saved ourselves about $4000.00 by having them do the install from the start. Hindsight is always 20/20 foresight is never that good.

    Best of luck!
  4. aaronwiles1

    aaronwiles1 Guest

    Tim,

    What is the 1" releif? HVAC is all new to me. This is one area I possibly will outsource, or at least have help with. I have to have one come out anyway and give me a quote for a new unit upstairs. (A month and a half after buying this house, the upstairs unit fried :( )

    As far as the knife, I think they make a utility knife that has a 45 deg. blade. I'll check into it.

    The super duct stuff...I'm having problems trying to find it on Johns Manville website. I don't know if they are using a different name for it or ???

    Thank you for your feedback. I'm not far from having to run this duct work.

    Aaron
  5. timmayock

    timmayock

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    Aaron,
    the relief is a way to join 2 peices of duct together. It is a notched end.
    one side has the notch on the inside and the other has it on the outside.

    I got the superduct myself from a HVAC distributor. It takes some digging to get the right source.
  6. aaronwiles1

    aaronwiles1 Guest

    Tim,

    I can see where you would use something like this on metal duct work. So is this also true w/ just butting together the board stuff as well? Is it a metal piece or ???

    Or do you just butt together the fiberglass board and tape/seal it together? And use a hanging support to hold the weight at the seam?

    Thanks,

    Aaron
  7. timmayock

    timmayock

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    Aaron,
    It is simply cut out of the fiberglass middle of the piece of duct on the long 10' edge of the board.

    This is done at the factory. There is still foil on the female relief, it is best to fold back the foil and tape it to the male mating piece of duct.
  8. aaronwiles1

    aaronwiles1 Guest

    Just wanted to bump this up. Looks like Rod is back from vacation :D Hope all is well.

    Rod, can you give any insight or suggestions here?

    Thanks,

    Aaron
  9. Rod Gervais

    Rod Gervais Moderator

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    Hi Aaron,

    Actually you have gotten the best advice you could already.

    HIRE AN EXPERT....... and i do not mean just a contractor.

    You need a good mechanical engineer - preferably someone who has experience in these designs - Tim's engineer designed a state of the ART movie studio for me a few years back - as well as a national museum........ he knows "quiet" real well. I also gently guided him through the process to make certain that fresh air and static relief were properly dealt with.

    Then - if you want to try it yourself (personally I would not reccomend it) we can give you some pointers here........

    Rod
  10. aaronwiles1

    aaronwiles1 Guest

    I had the AC guy out Saturday to look at what I have going on. He made a few comments on the bends, etc for the returns. Being in Nashville, he's worked w/ studio installs before, so he knows what I'm trying to achieve.
  11. aaronwiles1

    aaronwiles1 Guest

    I'm reviving my thread. Ok, I got the AC guy out, and the quote to rerun just duct work is about $1400. For as much as I'd like to have someone else do this for me, the budget has gotten a little tighter.

    So, I'm going to attempt some of this on my own. I got some good pointers and ideas from the AC guy for returns.

    Here's what I have questions about now:

    1. For the send, I need a short height (6"-8"), but width I can go approx 24". What type of grill would I need to install for this type of area and what is the "rough in" i need to make the hole?

    2. Same question for the return. What is a recommended size and grill section I can use for the control room. Steel Studs are on 24" center.

    If you need some idea of what the area looks like, click here:

    http://johnlsayers.com/phpBB2/viewtopic.php?t=839&postdays=0&postorder=asc&start=178

    or

    http://johnlsayers.com/phpBB2/viewtopic.php?t=839&postdays=0&postorder=asc&start=211

    3. How do I decouple the duct work from the drywall or framing of the wall? Or is this even possible?

    4. Do I use the super duct stuff the entire way, or do I integrate it w/ some flex duct at some point?

    Thanks,

    Aaron
  12. Gibs Son

    Gibs Son Guest

    Aaron,

    A few clarifications will help me to better understand your system. Forgive me if they have already been covered in the 15 page thread you linked too.

    Is the AC shown a dedicated system for the studio or does it also serve the house? What are the sizes of the studio and control rooms?

    What size is the unit? It looks like a Trane, but what’s the model?

    Is there turning vanes installed at the top of the vertical duct rise? If not, there should be. The horizontal run looks like it will be internally lined rectangular metal duct, correct? What’s that piece of floppy laying the vent stack for, a supply duct? Out of curiosity, did a professional install that vent stack? Long horizontal runs of vent pipe are tricky and can easily become a fire or monoxide hazard. Just want to make sure your code compliant and safe! (Max horizontal length= 75% of height as measured from connector at unit to the bottom of vent cap. An angle of 45 degrees or more is considered horizontal. Min slope of 2 degrees slope) What about combustion air into the mechanical room? Has that been addressed? Can you post another picture looking from the room at the AC unit? ( Looking into the RA duct prior to the Electronic Air Cleaner)


    >1. For the send, I need a short height (6"-8"), but width I can go approx 24". What type of grill would I need to install for this type of area and what is the "rough in" i need to make the hole? <

    Will you be installing sidewall grilles or ceiling mounted? How much CFM do have for each room? How many inlets/ outlets per room will there, or can there be?

    2. Same question for the return. What is a recommended size and grill section I can use for the control room. Steel Studs are on 24" center.<

    Same questions as above. Can you get your HVAC guy to purchase the grills for you?


    >3. How do I decouple the duct work from the drywall or framing of the wall? Or is this even possible? <

    If your using duct board I would not worry about it. Otherwise a simple canvas connection will do the trick. The photos raise another flag in my mind. What about fire dampers? If your studio will be used as a public space then you certainly have a separation of occupancy which would require fire dampers. If your going to run a business in there and have paying customers in your studio you really should check into you liability.

    >4. Do I use the super duct stuff the entire way, or do I integrate it w/ some flex duct at some point? <

    If your going to sidewall feed the rooms I would just keep with properly sized duct board, fewer transitions will be required.

    If you can stand it, check out my rather long-winded next post in which I will explain some HVAC basics. This should give some insight to general design practices to follow.

    Peace,
    Gibs.
  13. Gibs Son

    Gibs Son Guest

    I have read some HVAC related threads on this site. The advice I have seen has ranged from sound, no pun intened, to poor. I hope the following information will help clear up some issues, as well as create some thought and educate those whom know little or nothing about HVAC design basics. It is not ab all emcompassing document, but should give the HVAC challenged some insight and ammo when discussing their needs with a local contractor or design proffesional.

    If you’re trying to achieve a RC of less than 20, but not less than 15, then rectangular duct systems located above gypsum board ceilings should not exceed a maximum duct velocity of 1000 fpm (feet per minute). If it’s a round duct system then up too 1500 fpm may be used. Lower velocities are required if the ducts are above acoustical tile, and even less if they are exposed. These values also assume a minimum of ½ insulation is wrapped around the duct. Better yet, line the ducts ½” to 1” of acoustical lining.

    The final 7-10 feet of branch ducts serving inlets/ outlets will require much lower velocities. In many respects the final velocity of the duct will depend upon the free area of the inlet/ outlet. A final duct velocity of three hundred to 500 fpm is pretty safe bet for just about all inlet/ outlet’s I can think of except some perforated ceiling grilles. I have never seen a cut sheet on the stuff that Home Depot and the like sell, so do your homework. I recommend purchasing from a HVAC supply house or a local contractor who understands and has access to performance specs for that particular inlet/ outlet.

    While on the subject of inlets/ outlets, it’s important to understand that every time you add a new inlet/ outlet to a space, the mfr.’s published NC goes up, and so goes the room NC. Select inlets/ outlets that will result in a cumulative noise criterion (NC) of less than the RC you are trying to achieve. For example, if an inlet/ outlet has a NC of 10 at a published terminal velocity, that same device will be at NC 13 once you add another identical inlet/ outlet in the room. (<==Rule of thumb.) This is especially true when the inlet/outlet are within 10 feet of one another. When multiple diffusers are grouped together in a large space, the sound of the air devices are additive by up to 10 [log(number of devices)]. Additionally, the mfr.’s published data is based upon a 9’-0” ceiling, so if the ceiling is 8’-0” you need to extrapolate. The inlets/ outlets should be tested in accordance with ASHRAE Standard 70-1991 and the Air Diffusion Council Test Code 1062. There are other factors that will affect the NC added to the room from an inlet/outlet, and should be considered on a per project, per inlet/outlet basis, and preferably by an experienced professional.
    Side note: never, under any circumstances should you allow an opposed blade damper to be installed on a inlet/ outlet when noise is of concern.

    Air distribution is as much an ART form as it is a science, and even more so when it comes to high volume spaces. When it comes to air distribution, high volume spaces present many challenges. A greater emphasis must be placed upon diffuser/ grill selection and placement. Manufacturers standard published data in regards to throw patterns no longer apply, rather, horizontal and vertical jet projections become the criteria to be analyzed. As a general rule, you don’t want airflow in excess of 50 fpm hitting people while cooling, 20 fpm during heating mode. Consequently, heating and cooling airflow performance must be evaluated separately because a downward jet of cold air will travel further, hot air less, than isothermal air.

    Location of supply and return outlets is crucial in studios and control rooms, not only because you don’t want air blowing on microphones or people, but because heating and cooling airflow characteristics are so different. Other important factors are inlet/ outlet proximity to corners and whether or not it’s a side wall, floor or ceiling mounted inlet outlet.

    The duct layout should incorporate the use of 45's instead of 90-degree elbows wherever possible. Do not arbitrarily add elbows and 45’s believing that they will reduce sound transmission. More often than not, all your doing is increasing turbulence and static pressures, which force the fan to work harder and increases the sound level anyway. Straight lengths of ductwork of at least 5-10 duct diameters between elbows, transitions, dampers etc., as well as room outlets, is one of the most important design practices to follow when trying to reduce aerodynamic duct noise. In critical environments, it doesn’t hurt to design to 8-12.

    Side note: If at all possible have the duct system sized using the Static Regain Method. This method of sizing ductwork requires allot more work during the design phase, and usually ends up with slightly larger ducts, but in the end it has a much greater propensity towards self balancing than does the usual, and all to often used, Equal Friction Method. Because the system lends itself towards self-balancing, balancing dampers inside the duct can often be omitted. This cannot be done with any other method of duct design.

    Other useful tidbits: size duct and duct elements for low velocities: Avoid abrupt changes in airflow direction by using 45's everywhere possible. Use low loss fittings as outlined by SMACNA or ASHRAE.: Air balance the system for the lowest possible fan speed with the dampers generally open.

    In a perfect world each room would have a separate duct run from the source equipment inlet/outlet but that is rarely feasible. If at all possible, supply/ return ducts should originate from the main trunk and not serve any more than one room at a time. Duct Sound Attenuaters may be considered in larger systems, but may be cost or space prohibitive.

    Although flexible duct can reduce airborne noise, flex duct does need to be kept to a minimum and maximum length. Three to six feet in length is standard. Some contractors and a DIY’ers might want to install longer lengths because flex duct is inexpensive, but I highly recommend that you don’t. It is important to keep flex duct straight. Notice I did not use the term “as straight as possible”. Where bends in the duct are required, they need to have as long of a radius as possible. A misaligned flex duct to a diffuser can add as much as 15 dB to that devices sound level.
    Some engineers wont use flexible duct above sound sensitive areas because of the potentially high breakout sound levels associated with flex duct. I'm of the opinion that the use of flex duct needs to be discussed with the owner and viewed on a case by case basis.

    The main supply and return air duct’s connection to the air handler should not be made by means of a rigid attachment. Duct rumble can, and does occur in the 16-100 Hz range. This is especially true when there is a dramatic change in airflow direction near the fan. Adhere to either ASHRAE or SMACNA’s outlet configuration design guide for fans to minimize any unwarranted problems in this regard. Consider yourself forewarned, ducts with internally lined sound insulation, duct mounted sound attenuaters or externally wrapped duct will NOT eliminate or reduce duct rumble caused by a poor duct connection.

    The air handler should have vibration isolation. A floor-mounted system on concrete can introduce low frequency rumble into the building if they are not somehow decoupled.
    Refrigerant piping, condensate lines, gas lines, and electrical conduit and are all sources of sound transmission and are often overlooked. None of these should have a rigid connection to the unit.

    Variable flow systems such as VVT, VAV, etc. can be useful and reduce energy consumption, however they do have pitfalls. Noise can be a killer, even if the design, control’s, installation and system balance are done correctly. The mechanical damper inside the Terminal Box will be modulating and will vary the pressure and velocity of the air in the duct. As these conditions change, the sound pressure levels of the box will change as well. The sound will be transmitted within the duct as well as radiate from the box into the ceiling space. Avoid installing any variable flow device in ceiling spaces, or anywhere near a room that would has an RC criteria of less than 40. If terminal boxes need to be located above a critical environment space, I would suggest a mockup first before closing up the ceiling.


    Peace,
    Gibs
  14. aaronwiles1

    aaronwiles1 Guest

    Hello Gibs,

    The unit shown is a dedicated unit for the basement. It is a Trane. It is gas heat. The unit is 1.5 ton (a little small, but I just bought this house and it came with it.) The unit is 8 yrs old. My upstairs unit fried a month and a half after buying the house :( And the window ac unit I had as a backup, fried last night :x

    Anyway, What are turning vanes? At this point, every piece of duct that is still attached this this thing is going to get removed from the unit before installing new duct work. So let's start with a naked unit.

    I know I'm going to have to bring in some fresh air from outside, so I guess I've got to knock a hole in the block.

    Oh, the total basement size is 1225 SF. The CR is roughly 18x16 at the widest points. w/ floating floor ceiling before drywall is roughly 87". I have a vocal iso that will be approx. 5 1/2' x 7 1/2' after walls. Other rooms will include 2 tracking rooms, the entry/kitchen/bar/extra tracking room as needed (all one room), and bathroom.

    The vent system on the unit was installed I'm assuming by whoever installed the unit 8 yrs ago. It was done to code at the time, as that's the only permit that has ever been pulled on this house in 30+ yrs.

    Once I have walls and ceilings up, I'll fork out the cash carbon monoxide detectors. The one I had was recently dropped and it's not working anymore. At least the warm weather is here now, so...

    I think the Ion cleaner or whatever it is quit working here recently. It won't even power on now. I don't know what's wrong with it?? I've got another roll of film I haven't developed yet. I'll try and get it done and posted. If you look on the 15 page thread, somewhere around page 9 or 10, there are some other pix that may show that. You'll see the electrical conduits from the panel coming out.

    Thanks,

    Aaron
  15. aaronwiles1

    aaronwiles1 Guest

    I forgot to mention the amp/power supply room. I'll need AC / return here too.

    Also forgot to mention that it wil probably be wall mounted not coming from the ceiling. I have a steel beam that is somewhat in the way of running duct work towards the front of the control room, so I'm going to have to place this duct on the back wall above where the broadband diffusor will go when I build it.

    The return will also be on the back wall near the door to exit the CR.

    I know I've forgotten another question or 2 you asked. If I forgot something else, ask, or if I find it after rereading again, I'll repost.

    "Edited" OK, what's the "RC" stand for in the world of HVAC?
    I think I got the one for "NC" (Noise Criterion)?

    The supplies for board, not a big deal. I know where to get board duct here in Nashville. The places I bought the Roxul also carry it.

    Ok, I'm going to sound like an idiot here...most of what you just posted, just went over my head. I picked up some of it, but I can learn fast. In fact, I consider it a challenge. Is there some links to the SMACNA or ASHRAE codes or design? Similar to what there is for the USG construction handbook. I'm sure it's got to be around on the web somewhere.

    Thanks again,

    Aaron
  16. aaronwiles1

    aaronwiles1 Guest

    I think I found one. I'm reading it now...

    http://www.energycodes.gov/comcheck/pdfs/403text.pdf
  17. Gibs Son

    Gibs Son Guest

    Crap, you edited your post! Oh well, based upon your original post:

    >What are turning vanes? <

    Turning vanes are installed inside rectangular ducts to assist airflow changes in direction, minimizing noise and static pressure. Starting from scratch I would install a square to round transition at the unit so the first turn I made was with round duct; if space permits.


    >I know I'm going to have to bring in some fresh air from outside, so I guess I've got to knock a hole in the block. <

    Correct, you will need outside air. But please don’t confuse outside air with combustion air, they are two entirely different matters. And, it looks like the unit might now be in a Confined Space, which can complicate matters. A confined space is defined as “ A space having a volume of less than 50 cubic feet per 1,000 BTU’s of the aggregate input rating of all appliances installed in that space” Key words here: Aggregate, appliances, and input. It’s pretty simple math but don’t forget about the cloths dryer being in the same room or water heater etc. Also, the input, not the output is what you need to consider.

    >Oh, the total basement size is 1225 SF. The CR is roughly 18x16 at the widest points. w/ floating floor ceiling before drywall is roughly 87". I have a vocal iso that will be approx. 5 1/2' x 7 1/2' after walls. Other rooms will include 2 tracking rooms, the entry/kitchen/bar/extra tracking room as needed (all one room), and bathroom. <

    Off the top of my head, with a 1.5 ton unit it’s going to be tight. You have one saving Grace, your in a basement. I saw some windows so I presume that at least five feet of wall is below grade? Which direction do the windows face? The unit you have will be capable of providing 500 to 700 cfm, depending upon balancing and static pressures. Since it looks like you will sidewall feed the rooms from the mechanical room, static pressure loss due to long duct runs and excessive turns should not be a factor. Let me go back and look some more at the photos so I can better understand which room is which. Maybe then I can give you some CFM numbers to shoot for.

    >It was done to code at the time<

    Then it’ probably ok and in compliance with the 92 UMC. However, you gotta realize that I am not familiar with your local codes and ordinances, especially what they were 8 years ago. Wouldn’t hurt to call your local building department just to find out what they were then and what they are now because according to most recent IMC, IBC and UMC, you will be required to bring your HVAC up to all the current standards. Better to be safe than sorry and have the inspector tell you to yank it all out during your final inspection.

    >I'll fork out the cash carbon monoxide detectors.<
    Don’t get the ones that are a Smoke Detector/ Carbon Monoxide ceiling mounted combo. CM is heavier than air so by the time the CM get’s to the ceiling, well you get the picture. Just MHO.

    >It won't even power on now. I don't know what's wrong with it?<

    Got Power? Internal overload protection ok? Is the door in place properly making the safety switch? If so, check the cells. If the cells are not seated just so those air cleaners wont come on. If it’s not one of these simple things you may want to call a contractor who works on them. That is of course unless you feel comfortable with forging your own path and troubleshoot the unit yourself. I’d get it repaired or replaced, those are great units. It’s a Honeywell right? That and an electrostatic air filter result in a virtually dust free environment.

    Let's see, you also wanted to know about links to ASHRAE and SMACNA codes and standards? First of all neither one are code. Many ASHRAE standards are adopted into code, but by themselves they are nothing more than "Standards". As far as links to the Standards, I dont think so. Im a member of ASHRAE but dont visit the site very much. Even when I have been to the site to try and find something I have had to either purchase the Standard as a seperate document or look it up in one of the Handbooks. There are a few exceptions, but none the less, I think you need to be a member of ASHRAE to get to those areas.

    As far as SMACNA, pretty much the same story except worse. I gave up on trying to visit their site 3 years ago. It was lame and kept promising grand updates but they never came. Im not sure if you can purhcase the SMACNA books without being a member or not.

    Oh, Energy Codes are NOT the same as design codes or standards.


    NC is Noise Criteria, RC is Room Criteria. For what your doing, they are exactly the same. I.E. NC 35 is equal to RC 35. The only time you really need to seperate the two is if you were actually performing calculations to determine the noise in a room.

    Anyway, let me go digest your photos and re-read my post. I thought I wrote it pretty plain english but perhaps I didnt. I did slap it toghther without much proofreading.



    Peace,
    Gibs
  18. z60611

    z60611

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    Hmm.

    I have a 13"x5" (65 in^2) rectangular duct feeding hot forced air, from which I intended to run four 6" insulated flexible ducts (113 in^2) about 20' using long soft S turns, i.e. 2 humps where the duct is moved 9 inches. So, this duct is 0" at 0', 9" at 5', 0" at 10', 9" at 15' and 0" at 20'. Basically just enough of a bend that I can't see through any part of it. There will probably be 90degree metal bends at both ends.

    My purpose with the flex duct is for sound attenuation, both from the furnace machine and from the room to the rest of the house.

    Are you suggesting that this is a bad way to go ?
  19. Gibs Son

    Gibs Son Guest


    Not knowing anything about the system type, equipment location and configuration, duct type and routing, air flow quantities, ceiling type, existing noise from surrounding equipment, and your personal noise level expectancy, just to name a few variables, it’s impossible for me to respond in an emphatic Yes or a No. Only you can make that determination.

    Quite honestly, for most homeowner types the 20’ of flex duct is not going to make an appreciable difference either way. Especially if the system serves the rest of the house as you say. The reason why is that the average home's main trunks were never designed with low velocity and sound attenuation in mind.

    Nonetheless, if it were my shared system, I would install acoustically lined metal duct, with a hard 90 off the main trunk, one 20’ straight run and then ninety into the grille/ diffuser. I would also install turning vanes in the elbows if it were rectangular duct, and locate the balancing damper right before the first elbow. If possible, make the final straight run of duct between the grille/ diffuser be 5-10 duct diameters long,

    If you know what CFM your working with I would be happy to quickly verify your duct size for velocities.


    Peace,
    Gibs
  20. z60611

    z60611

    Joined:
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    Location:
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    Gibs Son:

    Let's see.
    RSIC walls, with 3 layers on the inside and 2 layers on the outside.
    Kinetics ICW ceiling with 3 layers and 15" of space.
    Kinetics RIM floor, wood, inside the walls.

    I don't want to hear the furnace, or the wind, nor the noise of the room to escape. I expect the former two, but the latter will probably not be perfect givin the 85db 20hz room.

    Certainly the walls/doors are plenty to defeat furnace noise. Even though the furnace is right beside this room, and the main duct runs along and just outside the wall of this room.

    The 13x5" rectangular duct that runs off the main 12x8" duct goes over another equipment room that's outside of the quiet room. The 13x5" duct is 36" from the furnace down the 12x8" duct. The 13x5" duct is 10' long. It is not lined, but it is decoupled with a fabric. The furance is mounted on 1/2 rubber feet. The return air, and the main duct are also decoupled with fabric.

    The furnace, in 'continuous fan only mode' makes 50db(C) of noise at 6". I did a frequency distribution of the furnace, and it outputs a bell curve of noise with the loudest point around 630hz.

    The ducts, at the point I was talking about, should feed about 100CFM in 'continuous fan only mode'. Based on the estimated output of the furnace fan as provided by the manual at that blade speed, and then using a percentage of that for the 13"x5" duct vs the other holes in the main duct, and then deducting by 10% (as my guestimate of duct losses without bothering to look it up).

    Why on earth did I type all that? Here's a pic
    http://groups.msn.com/BobGoldsHomeTheatre/shoebox.msnw?action=ShowPhoto&PhotoID=18
    Please ignore the pic text, as it's out of date.
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