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  1. #1
    Join Date
    Feb 2010
    Posts
    5

    replacement heat pump and adding new vents

    I am in Florida in a 40 year old house. My 10.5 year old Lennox heat pump with air handler installed in garage attic has never been particularly reliable -- has always required service almost every year. With 10 year parts/labor from my local AC company, all was fine. With the $1500 tax credit, I would like to replace the system even though it is currently running fine. I got quotes from my current company, one other big local outfit, and Sears.

    A few years ago, I added 300 sq ft of living space (80 sq ft space plus 220 sq ft space). I need to up the size of my system from 3 ton to 3.5 ton and I want to add new ceiling vents in those 2 rooms.

    I am considering replacing all the duct work in the attic with new flex ducts. The system now is very unbalanced with rooms at the far end of the house getting very little air. I thought I needed new ducts to solve this problem. 2 of the quoting companies did recommend replacement and the 3rd said the ducts were fine and that they could add 2 new vents and still balance the whole system. To my layman's mind, that seems unlikely. BTW, I have seen the duct work sweat a lot of water right through the paper covered insulation in the summer. It seems like modern use of distribution boxes and dampers is better than what I have now.

    So my main question right now is, do you think I can really get away with current duct work and get 2 new vents off of it, or is replacement of all duct work really the only option?

    Thanks.

  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,314
    You might not need a larger A/C.

    Just a proper duct system.
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    How many times must one fix something before it is fixed?

  3. #3
    If the ducting is of proper size and is in good condition. I would recommend staying with the current size and zoning the system. Carrier Infinty system is awsome! Use a long standing Carrier dealer in your area not Sears. If you wait til March the Carrier rebates come out and you could save even more $$$$ including the tax credit.

  4. #4
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,323

    Question Specifics ... ?

    Quote Originally Posted by artsd View Post
    I am in Florida in a 40 year old house. My 10.5 year old Lennox heat pump with air handler installed in garage attic has never been particularly reliable

    A few years ago, I added 300 sq ft of living space (80 sq ft space plus 220 sq ft space).

    I am considering replacing all the duct work in the attic with new flex ducts.

    The system now is very unbalanced with rooms at the far end of the house

    To my layman's mind, that seems unlikely. BTW, I have seen the duct work sweat a lot of water right through the paper covered insulation in the summer.
    It seems like modern use of distribution boxes and dampers is better than what I have now.
    Sq. Footage _ _ _ _ _ _

    # of windows & sliding glass door(s) on each side of the house
    _ _Windows _ _Doors__
    i.e.
    N 2 _______ x
    S 3 _______ x
    E 4 _______ x
    W 4 ________ 2
    Total 13 ________ 2

    Have the windows every been Replaced?
    _________________________ Tinted?

    Do you set the thermostat to 78'F in summer?
    If not, it is set @ _ _ 'F.

    Does the current system maintain this setpoint in mid-late afternoon?

    Does the current system maintain < 45% relative humidity?

    I doubt that an additional 300 square feet would need a unit to be upsized
    when other mitigating efforts could be pursued.

    Air distribution could likely be improved with a longer supply header.
    Last edited by dan sw fl; 02-04-2010 at 07:03 PM.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  5. #5
    Join Date
    Feb 2010
    Posts
    5
    Thanks for the replies everyone. The house was originally 1650 and is now about 1950 sq ft. My current system is 3 ton 10 SEER (I think that is the SEER rating).

    Sears used a thorough looking computer program where a lot of variables were entered including sq footage, glass, house orientation, etc.. His software calculated about a 3.2 ton unit was needed. BTW, it was Sears who said I could use existing duct work.

    I do have a well respected local Carrier dealer -- the ones who sold me the Lennox 10 years ago. They quoted on a middle line Carrier system (Performance). Is the price increase to Infinity worth it?

    I am usually able to maintain my desired temp in summer (but system is always on it seems).

    What about sweating ducts? It seems like re-insulating is more work than replacing.

  6. #6
    Infinity is worth every dime! The rebate is a really nice chunk of change. If your Carrier dealer doesn't offer it then call a different dealer. Check the Carrier web site for Dealers and rebates. Keep in mind the zoning. If you don't do it now, but may in the near future. Make sure you purchase the Infinity zoning stat it will function with or without the zoning system in service but, the standard model will not work with the zoning system.

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