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Thread: system sizing question

  1. #1
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    system sizing question

    First post, been lurking a bit & looking for advice from some pros.

    My system is original-- a 22 year old Amana "4 ton" system and the evap coil is leaking, condenser fins are brittle, etc. But I say "4 ton" in quotes because I pulled all the model #s and specs for all the important pieces:

    4 ton condensor coil
    42000 BTU compressor (3.5 ton)
    3.5 ton evap coil (CHA42TSC)
    1450 CFM blower (3.5 ton @ 400 CFM/ton)

    Appears to be a piecemealed system. I'm not the original owner, but the original owner saved all paperwork and I found the coil was originally a 3 ton and had problems with ice, so the builder replaced it with a 3.5 under warranty. But I digress...

    Been working with contractors and they want to sell a complete 4 ton or even a 5 ton system. So I pushed them farther & got some model #s for the condensers, evaps & air handlers, and these are fully 4 or 5 ton systems, both with increased BTU and CFM.

    I am in notorious Houston, TX where humidity removal is the most important thing. This old system has a 22 degree difference between supply and return, and will keep humidity at 45-50% and I'd like to keep it that way. Afraid going full 4 ton will cycle and won't remove humidity. I've been in cold clammy apartments with oversized units and it sucks!

    So my question is- should I get with these contractors for a complete 3.5 ton system instead?

  2. #2
    Join Date
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    Personally without a load calculation I'd go 3.5
    Unless redoing all ductwork going bigger is a mistake as your current ductwork is likely marginal at best
    You don't squat with your spurs on.
    And you NEVER put the torches away before pressure testing.

  3. #3
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    Post the actual model number of the condenser.

    A 42,000 BTU compressor. May be rated that at 105, or 130 condensing temp. So the condenser model number is important.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  4. #4
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    Thread Starter
    Quote Originally Posted by beenthere View Post
    Post the actual model number of the condenser.

    A 42,000 BTU compressor. May be rated that at 105, or 130 condensing temp. So the condenser model number is important.
    So that is an Amana RCC48A2B.

  5. #5
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    Okay, you currently have a 4 ton system.

    A new 4 ton could have a compressor rated at 40,000 or 42,000 BTUS . Depending on unit SEER/EER rating.

    You never go by compressor rating only.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  6. #6
    Join Date
    Nov 2004
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    Quote Originally Posted by former_weedhead View Post
    First post, been lurking a bit & looking for advice from some pros.

    My system is original-- a 22 year old Amana "4 ton" system and the evap coil is leaking,
    condenser fins are brittle, etc.
    But I say "4 ton" in quotes because
    I pulled all the model #s and specs for all the important pieces:

    4 ton condensor coil
    42000 BTU compressor (3.5 ton)
    3.5 ton evap coil (CHA42TSC)
    1450 CFM blower (3.5 ton @ 400 CFM/ton)

    Appears to be a piecemealed system. I'm not the original owner, but the original owner saved all paperwork and I found the coil was originally a 3 ton and had problems with ice, so the builder replaced it with a 3.5 under warranty. But I digress...

    Been working with contractors and they want to sell a complete 4 ton or even a 5 ton system. So I pushed them farther & got some model #s for the condensers, evaps & air handlers, and these are fully 4 or 5 ton systems, both with increased BTU and CFM.

    I am in notorious Houston, TX where humidity removal is the most important thing.

    This old system has a 22 degree difference between supply and return,
    and will keep humidity at 45-50% and I'd like to keep it that way.

    Afraid going full 4 ton will cycle and won't remove humidity.
    I've been in cold clammy apartments with oversized units and it sucks!

    So my question is- should I get with these contractors for a complete 3.5 ton system instead?
    Age of Residence ___
    Square Feet per Floor ___ .. ____


    R-13 Walls ?
    R-30 Ceiling ?

    # of Windows
    North
    South
    East
    West

    Double Pane ___
    Single Pane

    Tinted __ ?


    Sizing/ MATCHED SYSTEM Selection depends on your responses above


    For Starters ...
    ______ Setup = 350 CFM/ Ton
    Designer Dan __ It's Not Rocket Science, But It is SCIENCE with Some Art. _ _ KEEP IT SIMPLE & SINCERE ___ __ www.mysimplifiedhvac.com ___ __ Define the Building Envelope & Perform a Detailed Load Calc: It's ALL About Windows & Make-up Air Requirements. Know Your Equipment Capabilities

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