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  1. #1
    Join Date
    Jan 2013
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    West Chester, PA
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    23

    Return duct and filter box

    The attached pictures are of the community return duct and filter box, installed in a new house last August.

    The filter box is 20X25, and I use 5" MERV 16 filters.

    From an airflow perspective, the widening of the duct above the filter, and abrupt narrowing after, seems incorrect. Specifically, the manufacturer of the filter box specifies a maximum angle of 20 degrees downstream of the filter, and this sheet metal far exceeds that. The other issues are that the duct the filter box is in is much smaller than the return trunk above it, and the fact that there are no turning vanes in the duct where it makes the 90 degree turn to the blower inlet.

    I would propose that, for starters, this sheet metel should be replaced with a straight 20X25 duct all the way up to the return trunk, and that turning vanes be installed at to ninety to the furnace. I'd appreciate any thoughts.
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  2. #2
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
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    2,737
    Actually, from what I see, it looks like a very nice set up. The radius elbow is great. No need for turning vanes. I really like the filter in that configuration. Much better than slapped on the side as most do. There was a lot more work in doing it the way they did.

    I saw an earlier post where you stated you were unhappy with the workmanship on your home's HVAC. It looks like they make their own ductwork. They must have some pride in what the do.

  3. #3
    Join Date
    Mar 2009
    Location
    Mount Holly, NC
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    3,290
    Quote Originally Posted by George2 View Post
    Actually, from what I see, it looks like a very nice set up. The radius elbow is great. No need for turning vanes. I really like the filter in that configuration. Much better than slapped on the side as most do. There was a lot more work in doing it the way they did.

    I saw an earlier post where you stated you were unhappy with the workmanship on your home's HVAC. It looks like they make their own ductwork. They must have some pride in what the do.
    This is TOTALLY incorrect.
    you have to radius the inner bend on a 90 to have ANY effect on airflow. without it, turning vanes are still needed...

    radiusing the outer bend only saves metal costs...
    The TRUE highest cost system is the system not installed properly...
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  4. #4
    Join Date
    Jan 2013
    Location
    West Chester, PA
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    Quote Originally Posted by vstech View Post
    This is TOTALLY incorrect.
    you have to radius the inner bend on a 90 to have ANY effect on airflow. without it, turning vanes are still needed...

    radiusing the outer bend only saves metal costs...
    Seems to be a professional difference of opinion on this point.

    I'm not an engineer but I think I have a basic understanding of fluid flow. If I were building the return drop in its present location, I would have made it the full 20X25 size of the filter box all the way up. and included turning vanes.

    With the overall leakage of the panned joists, I'm not sure if this would just be perfuming the pig, though.

    Thank you for any more thoughts.

  5. #5
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
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    Quote Originally Posted by vstech View Post
    This is TOTALLY incorrect.
    you have to radius the inner bend on a 90 to have ANY effect on airflow. without it, turning vanes are still needed...

    radiusing the outer bend only saves metal costs...
    Maybe in a perfect world. I'm not saying this is correct or right, but (almost) no one in my area (of maybe 350,000 people) get a radius elbow. They're lucky if they get a
    25"x 16" filter. Most will use the boughten 20"x 16" boot/drop. Turning vanes..........Right!! Not even on EAC do they use turning vanes.

    Why do the geothermal systems ask for a radius heel, but not the throat.........just curious?

  6. #6
    Join Date
    Feb 2009
    Location
    Tallahassee, FL
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    6,051
    I agree that job looks really very nice.

    However depending on how much airflow the furnace a/c is required it may or may not be slightly restrictive.

    What you propose to do would improve the air flow especially if you built a stand to let the bottom of furnace return as well instead of single sided entry.

    Oh and merv 16 is really restrictive hope you change it often.

  7. #7
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    68,308
    The return drop could be better.

    What size furnace and A/C.
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    How many times must one fix something before it is fixed?

  8. #8
    Join Date
    Jan 2013
    Location
    West Chester, PA
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    23
    "The return drop could be better."

    That was part of my point: the trunk is 28" wide, and the drop is 14X25 (turned so that the drop is 14 inches mated to the trunk's 28 inch dimension).

    "What size furnace and A/C."

    Here is the whole setup:

    XC16-048
    EL296UH090XV48C
    Harmony III, three dampers, three zones, one per floor (basement is conditioned space with its own thermostat)
    3 Comfortsense 7000 thermostats, one per floor/zone
    HCWP3-18 humidifier
    Lennox Healthy Climate filter box with 5" MERV 16 filter
    What I consider poor quality ductwork (leaky and restrictive in all the wrong places) with building cavities used as returns.

    All of this is new equipment installed last August.

    Is it the right size? Who knows--there's no evidence the installer ever did manual J or D calculations.

    I use Lennox X6675 Carbon Clean HCF20-16 MERV 16 filters. The manufacturer recommends replacing them yearly, but I replace them at the beginning of each quarter. Which should tell you something about where I sit on the IAQ versus cost spectrum. Downstream of the filter, the manufacturer specifies a maximum narrowing of 20 degrees, or no more than around 4 inches per linear foot. This installation is about double that. I know what you're thinking, what does some PE with a fancy calculator know about airflow in the real world--still, one has to wonder why, if you're going to go to all this trouble, why not build the drop at the 20X25 dimension of the filter box all the way up and down? That, to me, doesn't show attention to detail, it shows a desire to cut corners on sheet metal (no pun intended).

    As I wrote elsewhere, I have lots of other issues with the system. If you zoom in on the pictures you may notice the unsecured wires going to the humidifier and humidistat. That's where I had to build my own circuit to get the humidifier to operate--after two attempts, the installer hadn't gotten it ever to come on (and wasn't going to, the way he wired it) and I really didn't want them back in my house. I'll try to secure the wires this afternoon--as you might guess, I have lots of other demands on my time and this wasn't how I imagined spending weekends in my new house.

    This is really better discussed in the other thread I started, but all of the ductwork, especially the panned joists for returns, are leaky. I've been sealing them myself, working my way out from the furnace and paying a lot of attention to the boots in the first floor, which were all left with holes you could drop a pen through to the basement. I have concerns about a long list of other things which may or may not be correctable at any kind of sensible cost, like the upstairs supply trunk running vertically through the garage; and the zone 2 thermostat being located in the upstairs hallway, far from the nearest supply or return, and subject to complete isolation from conditioned air if all the bedroom doors are closed. And so on.

    I don't want to come off sounding like an overly picky homeowner. I wanted a top quality system (which for me, begins with ductwork) and I was happy to pay a fair price for craftsmanship. I don't think "craftsmanship" is the adjective that comes to mind when I look at this system. Hopefully, this conversation will be helpful in locating a detail oriented HVAC professional in my area who doesn't mind working over someone else's messes. In the situation I found myself, I was stuck with an installer who didn't answer to me, and whom I couldn't replace, and whose outrageous markups on equipment I was stuck with. (He tried to be as opaque as possible but you know, equipment costs to dealers aren't really a mystery these days). Either way, I really do appreciate the comments.

  9. #9
    Join Date
    Jan 2013
    Location
    West Chester, PA
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    23
    You might have also noticed the large sheet metal patch just above the filter box. That patch is my work too. That was the installer's idea of where to put the single return for the basement (zone 3). When that was open, with a register over it, the return airflow from the top two floors was pretty much zero. As you might imagine.

    At least I had the foresight to put a ton of 4 foot flourescents by the equipment so I can see what I'm doing. Be even happier if it were a professional making use of the lighting, though.

  10. #10
    Join Date
    Jan 2013
    Location
    West Chester, PA
    Posts
    23
    I'm asking these questions because I'm genuinely interested in your opinions. So I appreciate all responses.

    To help with your assessment of the ductwork, I'm sure pictures are always helpful. The following are a typical floor boot the way the installer left it, and one after I sealed it up. The first one I did took me about two hours, using metal tape and zero VOC clear sealant. Fortunately, I'm getting faster.

    Also, just for fun, I attached two pictures of floor registers. Before is how it came and after is modified my removing the register damper and actuator, and sealing and insulating the edges so it fits tightly in a sealed boot. The registers of course are not the point of this discussion.

    As a point of information, the basement (zone 3) is OFF at its thermostat. The furnace is in the basement. With the fairly small amount of sealing I've done, the basement temperature has dropped by three degrees (at the same outside air temperature).

    All comments on ductwork are appreciated but here's a specific question: what do you think of using building cavities for return ducts?
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  11. #11
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
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    7,445
    Quote Originally Posted by homeownerjim View Post
    I'm asking these questions because I'm genuinely interested in your opinions. So I appreciate all responses.

    To help with your assessment of the ductwork, I'm sure pictures are always helpful. The following are a typical floor boot the way the installer left it, and one after I sealed it up. The first one I did took me about two hours, using metal tape and zero VOC clear sealant. Fortunately, I'm getting faster.

    Also, just for fun, I attached two pictures of floor registers. Before is how it came and after is modified my removing the register damper and actuator, and sealing and insulating the edges so it fits tightly in a sealed boot. The registers of course are not the point of this discussion.

    As a point of information, the basement (zone 3) is OFF at its thermostat. The furnace is in the basement. With the fairly small amount of sealing I've done, the basement temperature has dropped by three degrees (at the same outside air temperature).

    All comments on ductwork are appreciated but here's a specific question: what do you think of using building cavities for return ducts?
    Using building cavities for returns is old school and not good. I do blower door tests and the worst leakage duct systems are panned returns or building cavity chases used for return air. I'm pretty sure it's against code to use building cavities for ducting.

  12. #12
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    Jan 2013
    Location
    West Chester, PA
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    23
    Quote Originally Posted by jtrammel View Post
    Using building cavities for returns is old school and not good. I do blower door tests and the worst leakage duct systems are panned returns or building cavity chases used for return air. I'm pretty sure it's against code to use building cavities for ducting.
    It ought to be against code, that's for sure. I think it's permitted in my part of Pennsylvania, but I'll find out for sure. I was dismayed when I saw what they'd done but as I explained earlier, I was stuck.

    I'm trying to get an audit done so I can find out exactly how bad the leakage is. And manual J calculations, which I don't believe were ever done. The question becomes what can reasonably be done to improve the return air leakage.

    You guys that are pros at this, I think this conversation is maybe of interest. I'm someone that wanted the best HVAC system and IAQ I could get, and was perfectly willing to pay a fair price for quality work. Instead I got the same old junk from someone who really wasn't interested in finding out what I wanted and providing it for a profit. Typical of the conversations I had with this installer: I pointed out once that the insulation on the suction line had fallen off. He made a face and told me that that was "just there so the line won't sweat." Grudgingly, he agreed to take five minutes to secure a new piece of insulation with six zip ties.

    To put it mildly, I didn't appreciate being treated like an idiot. Doesn't it make more sense to do quality work at a fair price? Again, I'm asking because I'm genuinely interested.

  13. #13
    Join Date
    Jun 2011
    Location
    Houston area
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    Quote Originally Posted by homeownerjim View Post
    .........I know what you're thinking, what does some PE with a fancy calculator know about airflow in the real world.........
    Quote Originally Posted by homeownerjim View Post
    .......I'm not an engineer but I think I have a basic understanding of fluid flow........
    I thought you were.

    Wow, close to a million bucks and you have to put up with that kind of horse manure?

    Other than the shooting, how was the play Mrs. Lincoln?

    Just a couple of comments;

    The floor boots looked pathetic.

    To me the return air duct looks odd with the filter where it is and they should've made it larger.

    Building cavities can be used for return chases if they are sealed properly but it's a last resort and not a best practice.

    Contract or not, I would have been on that builders a$$ like stink on a fresh turd. Totally unacceptable.

    If you can physically get to the ducts Aeroseal is a decent option.

    The insulation on the suction line is primarily to prevent sweating but the installers attitude says all, especially in front of a homeowner. Complete lack of professionalism. I'd bet a dollar he was young.

    Wireless thermostats are an option these days.

    Good luck Jim, keep us posted.
    The picture in my avatar is of the Houston Ship Channel and was taken from my backyard. I like to sit outside and slap mosquitos while watching countless supertankers, barges and cargo ships of every shape and size carry all sorts of deadly toxins to and fro. It's really beautiful at times.....just don't eat the three eyed fish....

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