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Thread: Air Flow

  1. #1

    Air Flow

    I think i have a problem with air flow. the return opening is 12" by 23" and the furnace is rated at 1600 cfm. The AC cycles on and off every 15 minutes respectfully. The thermostat is set at 79 but if i set it lower it takes longer to cool the house (1700 sq ft). I have a york h1zd model condenser that is 13 seer. it is a 410a system with a suction pressure of 127 and a head pressure of 245. I think i have adequate ducts coming out of the supply. i have four 6" ducts, one 10" and one 14" trunk coming out of the supply plenum. i have a feeling that the unit is starving for air. comments? suggestions?

    more information --

    The furnace and coil sit on a platform in the attic. the unit lays on it's side and an opening the size of 13" x 23" is cut out on side that lays on the platform. a 20" x 30" return plenum attaches to the bottom of the platform and a 20" x 30' return grill attaches to the bottom of that plenum. i think i need to add a 10" flex duct from the plenum to the unit since i can't cut the opening any larger.
    Last edited by squarepants; 08-04-2009 at 10:04 PM. Reason: more information

  2. #2
    Join Date
    Jul 2009
    Location
    Alabama
    Posts
    63
    Your return duct is approx. good for 1300cfms at best not taking into account any elbows or transitions etc. If it is internally lined it is only good for 900 cfms based on .05 static design. The supply mains add up to 1650 cfms based on .08 static design and not accounting for any elbows,fittings etc. What size and type is your return grille?

  3. #3
    Quote Originally Posted by DLR View Post
    Your return duct is approx. good for 1300cfms at best not taking into account any elbows or transitions etc. If it is internally lined it is only good for 900 cfms based on .05 static design. The supply mains add up to 1650 cfms based on .08 static design and not accounting for any elbows,fittings etc. What size and type is your return grille?

    i have a bar type grill and it is 20" x 30" but the opening in the plenum is 13" x 23" so i think i need to add another return grill to get more air. if i use a 10' flex, what size return grill should i get?

  4. #4
    Join Date
    Jul 2009
    Location
    Alabama
    Posts
    63
    Not a DIY site. You need a tech to check for proper static and total cfms.

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