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  1. #1
    Join Date
    Jun 2005
    Posts
    5
    The heat pumps in my older (1940's) central Florida home are shot and must be replaced. It's a 2 story home with 2 central units, little to no insulation, and lots of windows. Have had 3 estimates. The first guy sells Trane and Rheem and recommended 2 ton Rheems, 12 seer. Said that would give me the best bang for my buck. The 2nd guy sells only Rheem and recommended 2 ton Rheems, 13 seer. The 3rd guy sells Trane and Rheem and recommended Trane, 14 seer, a 2.5 ton unit upstairs and 2 ton down. My questions: 1. Is there a significant difference in quality Rheem vs Trane? 2. Central Florida is hot and humid. What seer rating would make good sense? 3. The recommendation for a 2.5 ton unit upstairs has me confused. The guy took measurements and plugged it into a computer program. He said the recommendation was 2.3 but since they don't make them, he recommended 2.5. Should I be looking at a 2.5 ton unit?

    Many thanks in advance for any thoughts and/or suggestions.

  2. #2
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,429

    Arrow Sizing / Selection

    Originally posted by macavity
    The heat pumps in my older (1940's) central Florida home are shot and must be replaced. It's a 2 story home with 2 central units, little to no insulation, and lots of windows.
    What A/C equipment sizeS do you currently have?
    ( provide model #s / mfg)

    Will you add insulation?
    http://zipfoam.com/faq/index.html

    Will you add window tinting?

    What is the floor area and orientation of your house?

    How many windows and doors with glass on each side?
    Max.
    i.e 110 ___ S.F. facing East
    100 ___ S.F. West
    80 ___ S.F, North
    90 ___ S.F. South

    ... Seems like ~900 sq. feet each floor for 1st and 2nd floors.

    OR You can have someone perform a Manual J calc on your residence.
    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

  3. #3
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,613
    Both Rheem & Trane are excellent products. I prefer a scroll compressor and you won't find that in a 2 ton single stage Trane however.

    For Florida I'd suggest variable speed indoor units with whatever brand you choose. You can had a simple humidistat or a nice combo thermostat to slow the blower in times of high humidity. I wouldn't get too carried away on SEER. Take some of the money for a super SEER unit and put it towards insulation for example. Or window tint. Back to SEER, the Rheem RPMD-024 will reach 13.7 SEER with VS air handler, the RPMD-030 will reach 13.75 SEER. The RPMD is a nice unit, put one in for a friend's Dad recently.

    One thing to watch is exact unit capacity. Older units tended to be closer to the "ton" rating. A 2 ton would be 24,000 BTU. Nowdays, they aren't so you sometimes need a "2.5 ton" unit to get 25-26,000 BTU.


  4. #4
    Join Date
    Jun 2005
    Posts
    5
    Thanks for your thoughts. Currently have 2 2-ton units - a carrier about 22+ y/o and a janitrol about 18 y/o - neither work. The upstairs (where size of unit is in question) is a hair under 900 sq ft. There is about 4 inches of fiberglass insulation in the attic - no insulation in the walls - old stucco on wood lath. There are 14 windows in this space - 7 are on the south side, 5 west side, 6 north side and 6 east side. The downstairs has fewer windows, more protection from the sun, and is slightly smaller so a 2-ton unit does the trick.

    One of my original questions is whether I need a 2-ton or 2.5 ton unit upstairs. Now I'm wondering, should I look into more insulation? Also, what is a humidistat or combo thermstat?

    Thanks.

  5. #5
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,613
    If you get a VS blower, you can use a simple humidistat, like a whole house humidifier would use, to slow the blower when the humidity rises above set point. Pretty cheap way to do it. Now, several brands have thermostats with humidity control built in. Carrier started it with their Thermidistat, White-Rodgers and Invensys have it too. The stat lets you set desired humidity level. If it rises, the stat can signal the VS blower to slow down.

    Hard to say on sizing. If 2 ton has done fine all along, no point in going bigger. Often an upstairs has more cooling needs because the warm air rises from downstairs and the cool air from the upstairs A/C falls to downstairs so 1/2 ton bigger up probably won't hurt.

  6. #6
    Join Date
    Mar 2002
    Location
    Concord, CA
    Posts
    2,635
    Baldy is on the ball Mac. His comment was my question. Namely, does the existing two ton handle the upstairs? If so then you have empirical evidence that you don't need a 2.5.

  7. #7
    Join Date
    Jun 2005
    Posts
    5
    I will definitely check into the humidistat. Nobody has ever mentioned that before. As far as whether the old 2-ton did an adequate cooling job, I really don't know. It was bought and used as a rental, and I am just now moving into it.

    Thank you so much. Any other ideas would be greatly appreciated.

  8. #8
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,429

    Evaluation using Quick Load

    Originally posted by macavity
    The upstairs (where size of unit is in question) is a hair under 900 sq ft. There is about 4 inches of fiberglass insulation in the attic - no insulation in the walls - old stucco on wood lath. There are 14 windows in this space - 7 are on the south side, 5 west side, 6 north side and 6 east side.

    1.
    One of my original questions is whether I need a 2-ton or 2.5 ton unit upstairs.

    2.
    Now I'm wondering, should I look into more insulation?

    Using Room Temperature Set-point 74'F
    ...... Outside Design Temperature 93'F
    ................................ 19'F Delta T

    " Quick Load " Estimate

    1. Window Load....12,300 BTUh ~310 Sq.Ft.Total
    Ceiling Load... 3,000 assuming R-11
    Wall Load ..... 6,300 assuming R- 3
    Internal Gain.. 2,200 . People, equipment i.e TV, ..
    Misc. ....... 1,200 . Infiltration, duct
    Total Sensible. 25,000 BTUh
    for 900 Sq. Feet in Central FL
    Therefore,
    _ 2.8 Tons req'd based on Sensible Heat Ratio of 0.74

    .. I.M.H.O. HIGHLY
    _______ . Recommend 2.5 Ton MAX _____
    ...... considering Much Higher than normal glass area
    ...... and less than normal wall insulation.

    TRANE XL 16i .. 4TTX 6030 with 4TEE3F037.
    If Relative Humidity Is a concern.

    http://<a href="http://www.trane.com...XL16i.aspx</a>

    ALTERNATE: Depending on your budget,
    XR12 .. 2TTR 2030 with TWE031E

    2. Reducing the Wall Load to ~ 1/4 of existing
    ( R-3 increased to R-11) leads me to revise my recommendation to 2.0-Ton ..( 2.3 ton req'd after mod 20,600 BTUh Total)

    __ R-11 equivalent ... 2.8" of spray foam ...
    might be in the ball park of
    __ $ 1,600 for the walls only

    General undersizing of ~10% leads to improved humidity control.

    [Edited by dan sw fl on 06-04-2005 at 03:04 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

  9. #9
    Join Date
    Jun 2005
    Posts
    5
    Many thanks to everyone who has taken their time to pass along some advice. I really appreciate it. As my son says, "you can meet some pretty cool people on line." Since I need to do this a/c thing asap (gasp, it is very hot and humid here right now) I will go with the 2.5 unit upstairs, but, as time and money allow, I will follow-up with insulation and window tinting. Thanks again.

  10. #10
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Add the insulation to the attic ,now ,as adding it later will likely make the 2.5 ton,oversized.

    Dan's effort though noble,may not be the correct size ,and if it included R30 in the attic ,might be 2 ton.Insulation is the better way to go.


    Plus being in Florida there's a 70% chance that your duct system is too small ,and leaks a lot of cool air into the attic.Going larger requires a larger duct system,in most cases.Fixing the duct leaks ,helps with sizing as well.

    [Edited by dash on 06-05-2005 at 05:51 PM]

  11. #11
    Join Date
    Jun 2005
    Posts
    5
    Is there a significant difference (cost, effectiveness, longevity) in the types of insulation? ie foam, fiberglass, batt, blown, etc., etc.

  12. #12
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,429

    Lightbulb Insulation

    R-11 should be sufficient.

    Spray foam is a more effective vapor ( infiltration) barrier.

    http://www.zipfoam.com/pdf/ZIPFOAMBrochure.pdf

    R-19 is standard value of ceiling
    SPRAY FOAM insultation ( 5" ) for New Constuction.
    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

  13. #13

    Equipments sensible rating...

    Originally posted by Irascible
    Baldy is on the ball Mac. His comment was my question. Namely, does the existing two ton handle the upstairs? If so then you have empirical evidence that you don't need a 2.5.
    There are a lot of 2 tons systems out there that won't keep up to a 20 year old 2 ton just based on their capacity.

    You really need the advice and help of a persona knowledable enough to check this out for you...

    A 2 ton is not a 2 ton in all cases.... S
    AllTemp Heating & Cooling

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