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  1. #14
    Join Date
    Jun 2002
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    108
    Quote Originally Posted by bobb25 View Post
    Your return duct should carry ROUGHLY 1100 to 1200 CFM. Your return grill is rated at ROUGHLY (depending on velocity) 600 to 1000 FPM. Try removing your return air grill and see if the noise goes away.
    I don't have a grill on it yet, just a screen(screen door screen to prevent cats from adventures). It is not loud(not rattling or thumping), just the audible sound of a lot of air moving through an opening. It is only noticible in the hall where it is. I'm sure it will be louder with a grill(hart and cooley zero friction is on special order).

    How did you come up with these calculations? I thought it was something like 2 CFM per square inch on the duct size? I know the supply trunks(2) off the furnace are a combined 32 x 8. Both taper down along there runs. Returb is 26 x 8 the whole way until it enters furnace( gets larger) Not sure if this helps. They have another day left here, so I want to make sure anythingthat needs to be done is done. Thanks again for all the help.

    If the return duct is large enough, could I simply put another return opening on the other side of the wall? It would be aesthetically neutral. If so, how large?

  2. #15
    Join Date
    Feb 2007
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    Quote Originally Posted by roccol View Post
    I don't have a grill on it yet, just a screen(screen door screen to prevent cats from adventures). It is not loud(not rattling or thumping), just the audible sound of a lot of air moving through an opening. It is only noticible in the hall where it is. I'm sure it will be louder with a grill(hart and cooley zero friction is on special order).

    How did you come up with these calculations? I thought it was something like 2 CFM per square inch on the duct size? I know the supply trunks(2) off the furnace are a combined 32 x 8. Both taper down along there runs. Returb is 26 x 8 the whole way until it enters furnace( gets larger) Not sure if this helps. They have another day left here, so I want to make sure anythingthat needs to be done is done. Thanks again for all the help.

    If the return duct is large enough, could I simply put another return opening on the other side of the wall? It would be aesthetically neutral. If so, how large?
    A regular window screen causes more resistance than a return grill. Stand at a screen door or window on a windy day and then remove the screen and you'll see a big difference. Remove the screen from the return and see what it sounds like. I got those dimensions from a Southwark book they gave at seminar I went to years ago. Remember, those are rough numbers. There are a lot of variables.

  3. #16
    Join Date
    Jun 2002
    Posts
    108
    The screen makes no difference in this case. Sounds the same on or off. It the duct itself is large enough, I could easily put another 30 x 8 opening directly on the other side of the wall.

  4. #17
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    How big is your supply trunk duct? If you have more than one supply trunk duct, what are their sizes?

  5. #18
    Join Date
    Jun 2002
    Posts
    108
    Supply trunk 1: 14 x 8
    Supply trunk 2: 18 x 8

    Both taper down 4 inches in width at some point in the run.

  6. #19
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    Feb 2007
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    Quote Originally Posted by roccol View Post
    Supply trunk 1: 14 x 8
    Supply trunk 2: 18 x 8

    Both taper down 4 inches in width at some point in the run.
    I'm willing to bet that there's at least one take off on each of those trunks. If so, then you need at LEAST a 32 x 8 return duct. Get your contractor back and pay him to add some more return air.

  7. #20
    Join Date
    Jun 2002
    Posts
    108
    What do you mean by one take off? Also furnace is 2 stage. Reasonable quiet when fan and low stage is running. Obviously a little objectionable in stage 2.
    Also how can I test if static pressure is high without some sort of meter? Just to get an idea? Possible?

  8. #21
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    Feb 2007
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    You need to get your contractor back and address all these concerns with him.

  9. #22
    Join Date
    Jun 2002
    Posts
    108
    Yes of course. I just want to be armed with as much information as possible.

    So adding another opening to the return is not going to do much. I will need at least another 8 x 8 return. That may be hard to do in this old house.

  10. #23
    Join Date
    Feb 2007
    Location
    18951
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    Your contractor will be able to tell you what can be done. He can probably do almost anything, given enough time and money.

  11. #24
    Join Date
    Jun 2002
    Posts
    108
    Quote Originally Posted by bobb25 View Post
    If every contractor recommend a 26 x 8 central return, and you have better air flow now, then you did the right thing for heating. I just wonder why there’s no large return on the 2nd floor also, especially for cooling.

    Is it a loud bang when the system starts and stops, or more of a whistling sound?
    2cnd floor has a separate system. There are no bangs or clicks. Just the sound of air velocity, no whistling though.

  12. #25
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
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    18,836
    For two tons,the return duct and grille could be fine.

    #265 floor grille,Hart and Cooley,600 fpm ,.017 PD,at 800 cfms.

    8X30 duct,800cfms,.03 Friction Rate.

    Now your furnace may require more cfms.

    Model numbers??

  13. #26
    Join Date
    Jun 2002
    Posts
    108
    Furnace: Lennox GV32V5-100-5

    Dash the return duct is not 8 x 30, it is 26 x 8.

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