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  1. #1
    Join Date
    Jun 2011
    Posts
    6

    Right System Size?

    Hello. Newbie here.
    I have a 4500 sq. ft. 2-story house in the DFW area. It is 7.5 years old. I have two AC units outside; one large (1st floor) and the other small (for the 2nd floor). The problem is that on very hot summer days, the smaller unit for the 2nd story never shuts off. I can not even get the upstairs temperature down to 81 degrees when the sun is out. My house has tinted windows, adequate insulation and the best radiant barrier foil in the attic. I'm thinking the system installed in my house is not the right size. It is a Lennox. I was interested in any professional feedback. Thanks.

  2. #2
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
    Posts
    2,744
    Quote Originally Posted by tmd820 View Post
    Hello. Newbie here.
    I have a 4500 sq. ft. 2-story house in the DFW area. It is 7.5 years old. I have two AC units outside; one large (1st floor) and the other small (for the 2nd floor). The problem is that on very hot summer days, the smaller unit for the 2nd story never shuts off. I can not even get the upstairs temperature down to 81 degrees when the sun is out. My house has tinted windows, adequate insulation and the best radiant barrier foil in the attic. I'm thinking the system installed in my house is not the right size. It is a Lennox. I was interested in any professional feedback. Thanks.
    Questions first....How large is the 2nd fl. area? What is the A/C size for said area?

    Where is the furnace/air handler located for the 2nd fl. system? What size and where is the filter for that system?

  3. #3
    Join Date
    Jun 2011
    Posts
    6
    Here's what I know off the top of my head: both funance/air handlers are in the attic. I have two air filters for the first floor and two for the second floor. First floor are 20x30 and 16x25. 2nd Floor are 16x25 each.

    I will look up and post the missing information A/C size and 2nd floor area later this afternoon when I get home from work.

  4. #4
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
    Posts
    2,744
    Quote Originally Posted by tmd820 View Post
    Here's what I know off the top of my head: both funance/air handlers are in the attic. I have two air filters for the first floor and two for the second floor. First floor are 20x30 and 16x25. 2nd Floor are 16x25 each.

    I will look up and post the missing information A/C size and 2nd floor area later this afternoon when I get home from work.
    Thank you. So far, I like what I'm hearing. In my part of the world (the midwest) contractors provide a room on the second floor for the utilities.

    Does your house have a basement?

  5. #5
    Join Date
    Jun 2011
    Posts
    6
    No basement. Most houses in Texas are built on concrete slabs.
    I found the area (luckily I saved the blueprint). Total 2nd floor area is approx. 1514 sq. ft.

    I found this # on the side of the 2nd floor A/C unit:

    M/N 13ACC - 030 - 230 - 01

    I'm not sure if that is the right code to tell you the size.

  6. #6
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
    Posts
    2,744
    Quote Originally Posted by tmd820 View Post
    No basement. Most houses in Texas are built on concrete slabs.
    I found the area (luckily I saved the blueprint). Total 2nd floor area is approx. 1514 sq. ft.

    I found this # on the side of the 2nd floor A/C unit:

    M/N 13ACC - 030 - 230 - 01

    I'm not sure if that is the right code to tell you the size.
    It's a 2.5 ton. It should be doing the trick. Has it ever been serviced?

    Double check to make sure nothing has come apart in the attic.

    I saw a attic system not to long ago where it was pulling as much attic air as indoor air. Not too efficient!

    One more thing to check.....I need the size of the ductwork to the 2 filter grilles (for the 2nd floor system).

    Where are the return grilles located for the 1st floor system?

  7. #7
    Join Date
    Dec 2007
    Location
    houston, texas
    Posts
    3,787
    Here in Texas for some reason all the homes were built with the big unit downstairs and the small unit upstairs WHERE THE HEAT LOAD IS. Never could figure that out.
    I'm not tolerating Political Correctness anymore, from now on it's tell it like it is.

    Veto Pro Pak - The best tool bag you'll ever own






  8. #8
    Join Date
    Jun 2011
    Posts
    6
    Me neither. I guess they just go by square footage.

    The units in the attic have never been serviced. I think it's time.

    How do I determine the size of the ductwork? Just measure the diameter of the opening inside the grille?

  9. #9
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
    Posts
    2,744
    Quote Originally Posted by tmd820 View Post
    Me neither. I guess they just go by square footage.

    The units in the attic have never been serviced. I think it's time.

    How do I determine the size of the ductwork? Just measure the diameter of the opening inside the grille?
    Yes. Measure the diameter. Hopefully there's a seperation or some distance between the collar and the filter.

    Do the filters only get dirty (round circle) in the middle?

  10. #10
    Join Date
    Jun 2011
    Posts
    6
    The diameter of the circle for the ductwork is 12". No, the filter does not get dirty only in the middle.

  11. #11
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
    Posts
    2,744
    Quote Originally Posted by tmd820 View Post
    The diameter of the circle for the ductwork is 12". No, the filter does not get dirty only in the middle.
    Your 2.5 ton A/C needs 1,000 cfm. The blower is probably able to move 1,200 cfm. I like to size to the blower and then some.

    12" flex, run properly, and if it's not too long, will move around 450-500 cfm @ .08 static. As long as the filters are clean and not too restrictive, you are close to having enough.

    But most people here will tell you that more return is better than "barely enough" when it come to efficiency.

  12. #12
    Join Date
    Sep 2002
    Location
    Virginia
    Posts
    3,335
    Try this ... take those expensive pleated filters out and throw in those cheap blue see through filters.

  13. #13
    Join Date
    Jun 2011
    Posts
    6
    Ok, I will try that.
    Do you think the expensive pleated filters may be too restrictive?

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