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jbw35

A/C replacement

jbw35
10 years ago

We live in Atlanta in a 3000 sf two story house built in 2001. We need to replace our units so we received four quotes and they are very different. The last quote we had was to replace the A/C units only (the rest were for A/C and heat at the same time). So that's my first question, (1) if the heat is working fine now but is 12 years old, should we wait to replace them when broken versus now to get economies of scale. (2) The second question is we currently have 3 ton down and 2.5 up. the cooling has been fine for the most part though lately those upstairs complain that it is too hot. Should we get 3 ton for both? (3) the last quote was for upstairs 2.5 ton 16 SEER system single stage and downstairs 3 ton 2-stage 16 SEER. It was for carrier infinity. Does that sound right?

Appreciate any advice I can get.

Comments (4)

  • tigerdunes
    10 years ago

    Several questions.

    What size living area for downstairs and upstairs?

    How would you describe home's insulation and building qualities especially for upstairs? Attic insulation is good?

    Tell me about your existing furnaces; age, brand, model, size, efficiency, var speed or not.

    Post back.

    IMO

  • jbw35
    Original Author
    10 years ago

    The approx split must be about 1600/1400 because the den is open to the second floor and the foyer is open. The home was built new in 2001 so the furnace is that age. It's a basic Lennox system - builder minimum, but according to the guy who maintains it, it is in good shape. I never asked him how long he thinks it would last.

    The insulation is good. The ductwork has some re-routing to do because airflow in a couple of rooms is not as good as it could be. As far as heating goes, the upstairs hardly ever comes on because the heat from below in the open den area heats the rooms well enough. The lower level gets chilly but that's also because of the open den area, and the fact that the den air vents are mid wall instead of at the bottom of the wall. Also the air vents themselves are split in three with the 1/3 pointing left, 1/3 right and 1/3 straight.

    Does that help any?

  • udarrell
    10 years ago

    A heat gain/loss needs to be performed separately on both floors.

    Normally the first floor requires less Btuh to cool than the 2nd floor area; in your case that may not be the reality.

    Free Whole House or, 1st & 2nd Floor Areas' Load-Calcs performed separately.

    You can easily reduce infiltration rates yourself, therefore, IâÂÂd use 0.4 ACH (Air Changes per Hour) be sure to add the (Air Changes per Hour) CFM into the âÂÂFresh Air Recommended âÂÂline-slot, or it wonâÂÂt figure the Infiltration & fresh air Btuh.
    You can experiment with changing the design temperatures in both heat & cooling, (or start-over showing the New Retro-R-Values) also to see whether the equipment exceeds, at those particular temperatures & new retro conditions.

    You can't save the completed calc, so when you think it's right, Print it. The Snipping Tool can be used to capture an on screen image of the completed calc., which may be uploaded to this thread.

    The 2.5% summer design in Atlanta, GA is 92ðF & 74ðF wet bulb for about 43% RH; calc may show a lower design temp; use it.

    Here is a link that might be useful: Free Whole House or Floor Area Load-Calc

  • tigerdunes
    10 years ago

    "A heat gain/loss needs to be performed separately on both floors.
    Normally the first floor requires less Btuh to cool than the 2nd floor area; in your case that may not be the reality."

    I agree with above.

    Sounds like you have some ductwork sizing/design issues that should be pointed out to dealer for possible improvement.

    If you are satisfied with the heating, then furnaces can remain. But if they are conventional furnaces, you will be limited to 13 SEER condensers with matching coils. I would want a good model that has full cooling BTUs for the rated size. Many don't.

    IMO

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