Is the ac for my new house too small
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  1. #1
    Join Date
    Jun 2005
    Posts
    37
    1733 square feet, carrier 2.5 ton, live in Texas

    Tech has been out and ac is working fine. Just seems like it has to run all day. Plus it will not get the house to 72-75 on a 95 degree day

    floor plan
    ---------------
    http://www.perryhomes.com/homes/images/1733W_FP.GIF

  2. #2
    Join Date
    Apr 2004
    Posts
    7,680
    Chances are it wasnt designed to get to 72 on a 95 degree day, it was probably sized for 75-78 on a 95 degree day.

    Feel free to purchase and download HVAC-calc (blullseye at top of page), we cant guess based on square footage.

  3. #3
    as the previous poster pointed out:

    Systems are typically designed at an indoor temp of 75 F (78 F for Hi-velocity systems) with a swing of 3 F. During really hot weather, your house should hit 78 F or a little higher (but humidity will be low).

    Sounds like everything is fine.

  4. #4
    Join Date
    Jun 2005
    Posts
    37
    the problem is the ac can't even get the house to 75 on a 95 degree day. Aslo just to keep it at 80 it pretty much has to run the whole day.

  5. #5
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    There is a host of things that could be wrong.

    The most overlooked by techs ,is lack of required air flow.Give use the model numbers,main duct sizes ,return grille sizes,and brief description of the duct system.

    Use the laod calculation program on this site ,if the size is correct ,there is another problem.


    do you window coverings/blinds on all windows?It's usually sized assuming you do.

  6. #6
    Join Date
    May 2002
    Location
    Colorado
    Posts
    697
    Builder-installed system, right?

    No TXV, right?

    Amarillo, right?

  7. #7
    Join Date
    Jul 2001
    Location
    Gold Coast of Connecticut
    Posts
    4,568
    I have a 2 ton unit on 1850 sf in Connecticut and with 100% of the southern windows covered with room darkening shades I can maintain 75 degrees on 90+ degrees although we have a shorter number of hours it is beyond design. I would think you should be able to maintain 78. You unit should never shut down when at design temp, mine will run 12+ hours during really hot weather.
    Aire Serv of SW Connecticut- Gas heat, dual fuel and central a/c systems installed and serviced

  8. #8
    Join Date
    Mar 2001
    Posts
    287

    There may not be anything wrong with the a/c. What temp are you trying to get? I like 68-70 personally. I read your other post. It's worth it to blow in more insulation up to R 38-40. You need to do a heat loss/gain study with the software from this site. 2.5 tons sounds a tiny bit light for your house. Make the house fit the a/c....make sure you have NO duct leakage, good attic ventilation, and upgrade your insulation. Check your weather-stripping around doors and your window seals. Mine were terrible in my brand new house. I bet for $400 or so you can add extra insulation...

    You can always go to war with the builder, or pay another contractor to evaluate your current system. (good idea) Or you can get a 6000 BTU window a/c from the home depot or lowes --a really nice one too for less than $250. My neighbor did this for his master bedroom. (He likes to be able to cheaply zone off that room.)

  9. #9
    Join Date
    Jun 2005
    Location
    New York
    Posts
    207

    What??

    The man just bought a New House w/ central. Put in a wall or window unit??? OMG.

  10. #10
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,225

    Thumbs up Outline of " Quick Load " Calc

    Originally posted by smp7015

    1733 Square Feet
    2.5 Ton
    live in Texas
    Plan Review for One-Story
    No Sliding Glass Doors

    Direction # windows .. Area
    .................... Sq. Footage
    . Front ....... 1 ...... 20
    . Left ........ 4 ...... 76
    . Rear ........ 5 ..... 105 including 1 Door
    . Right ....... 3 ..... 58
    . Total .......13 ..... 259 S.F.
    . Front Entry Door ...Any Glass ?
    . Garage Entry Door ... Solid

    One should not expect >20'F dT cooling capacity with a appropriately sized unit.

    I am guessing the window area, but I would bet the actual total is Very Close to or slightly < 259 S.F.
    Glass area is likely > 210 S.F.

    My " Quick Load " calc approximates a formal Manual J.
    I also include "9 Person" + Infiltration loads.

    I can perform a realistic " Quick Load " if you provide the following:
    1. Front of House Faces ___ N S E OR WEST

    2. Wall Height ......_____ [ 8 or 9 feet ]

    3. Wall R-Value ......_____ [ 11 to 19 ]

    4. Ceiling R-Value...._____ [ 11 to 30 ]
    ......Note: R-30 would be Much More than
    sufficient for a southern climate

    5. Window Tinting ... ____ Yes / No
    ...... Dark ___
    (DARK = similar to sun glasses or Auto windows tinting)

    ...... Light ___

    SMP7015,
    Please verify 1 through 5.

    [Edited by dan sw fl on 06-23-2005 at 08:57 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

  11. #11
    Join Date
    Jun 2005
    Posts
    37
    Dan sw fl

    Thanks I would appreciate it.

    Front door has glass panes on it.

    1.)Front of house faces West

    2.)9 foot walls. Valted ceilings in the kitchen, living room, and master bedroom, entry way, master bath

    3.) Wall R-value I am guessing 18 but I am not sure

    4.) ceiling R-value 30 with 12 in adverage in attic

    5.) Window tinting none

    Thanks for everyone's help I appreciate it

  12. #12
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,225

    Thumbs down Larger Unit Required due to ...

    Walls and Ceiling R-Value used = 19
    Outside Temp. 97'F

    Load ....... BTUh
    Windows ... 14,600 ... 270 S.F. including Front Door
    Ceiling .... 3,830 ... could be higher due to Vaulted Areas
    Walls ...... 2,410 .. R-19
    Floor ........ 120 .. Negligible . slab on ground
    Duct ........4,120 .. R-6
    Infiltration.2,220 ..
    InternalGains2,770 .. ( Appliances, Lights,...
    People ......1,480 .. 5
    Total.......31,620 BTUh SENSIBLE

    Equates to a 3.5 Ton
    42,000 Total * 0.75 SHR = 31,500 Sensible

    Note that the windows are HALF ( 46%) of the total load which IMO is the usual case for CLEAR Windows.

    You may wish to pursue a Formal Analysis and even legal avenues, IF you are not able to acquire necessary enhancements through normal negotiations.
    A formal ACCA Manual J analysis can address the exact windows sizes, more specific R-values for ceiling with attic and vaulted ceiling characteristics.

    However, the bottom line is
    that based on 97'F Design Temperature ( ? ), 120'F attic for duct load, 270 S.F. Clear windows
    the Sensible Cooling Load is more than 31,000 BTUh.

    NO Matter which way a calculation is performed,
    a 2.5 Ton (30,000 BTUh Total, ~22,500 BTUh Sensible) system can NOT be justified.

    [Edited by dan sw fl on 06-24-2005 at 07:17 AM]
    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
    Join Date
    Apr 2004
    Posts
    7,680
    Ok, I get no where near that jusing J8.

    First off he has one window facing West (fron of house facing west) and it is under a porch overhang. One door facing West (front door) and the garage. On the south side he has 3 windows. blah blah blah, semi tight construction, infiltration 5 people 3 appliances in kitchen, I did the whole shmeal since you did R-30 ceiling r-19 in walls. Also using the room dimentsions, using wright draw, I come up with 1577 sq feet, it appears the garage is being considered in the builders sqare foot.

    I ploted his house identical to his link with the front facing West (bottom). on Right-Suite draw and J.

    I get....

    21,115 Sensible. with a CFM requirement of 1132 which would be about a 3 ton machine. I am not sure what you used for windows, and no sense arguing it but I think he should do his own to be sure.

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