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  1. #1
    Join Date
    Jul 2006
    Location
    SoCal-OC
    Posts
    33
    I'm in SoCal and planning to replace my really old Central AC sometime this year and doing all the background research so I hope I'm somewhat prepared when I start getting proposals.

    One of my questions has to do with return grille size and location. I currently have a 3 ton system (I think, it's from the mid 60's and the model # has no tonnage info that I can see) that I assume would be designed to run at ~1200cfm. The return is basically just a grille below the furnace closet door and is 24"x10". From what I can tell, this seems undersized to me (it does make a fair amount of noise in cooling mode) and figured based on grille data I've seen it's probably running around 900 fpm face velocity. Given the fact that my Man J calc showed I probably need 3.5 ton, I would think it might be a good idea to add at least another return somehow to reduce noise and pressure drop across the grille. There is a wall around the corner in the master bedroom that has direct access to the bottom of the furnace closet and might even be able to use a larger grille size. Would that be a acceptable location or would it be much better to try and duct a return or two in other locations of the house?

  2. #2
    Join Date
    Jul 2006
    Location
    conroe tx
    Posts
    19
    You can put a grill there but you might want to think about the noise.Is it posible to run a duct into the return chase from the attic and flex duct to ceiling filter grills.

  3. #3
    Join Date
    Jun 2000
    Posts
    97
    being that you have done so much research and really put a lot of time into this, If I were you I would remove the unit from the closet, put it in the attic, and make the return whatever size you have calculated it to be in the ceiling.

    and when its all said and done you have an extra closet and noise would probably not be a factor as long as your return is not too short.

  4. #4
    Join Date
    Jul 2006
    Location
    SoCal-OC
    Posts
    33
    You mean noise from air passing through the grill or noise from blower now directly entering the room? In either case, probably a good suggestion to think twice about that. Also, I realized if the bedroom door is closed it might limit the effectiveness of the return. I suppose I could think about running duct from the return chase to the attic and connect to a fairly decent sized grille in a hallway ceiling. Might be 20' or so away.

  5. #5
    Join Date
    Jul 2006
    Location
    SoCal-OC
    Posts
    33
    Twospeed- Interesting thought. I have no idea how difficult it is to move to the attic, but it might solve some problems. I'll have to think about that one.

  6. #6
    Join Date
    Jul 2006
    Location
    conroe tx
    Posts
    19
    I'm thinking noise from the blower. The door in the bedroom being closed shouldn't be issue if the other grill is in the hall.Another way to reduce noise is to cover the cement floor with ductboard.

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