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  1. #1
    Join Date
    Jun 2012
    Location
    Folkston, GA
    Posts
    6

    Is the Air Conditioner Oversized?

    1089 sq foot brick home built in 1954 in S.E. GA facing southeast with very little shade. On a Crawlspace with insulation between floor joists, blow in insulation in the attic about 6" deep, single payned wood windows, solid wood doors, blow in insulation attempted to be placed in walls, not sure of effectiveness.....

    Was originally built with a floor furnace and an Attic Fan. Not sure when the 3.5 ton central heat and air was installed but the installer said the date of the original unit was 2001. This was a Bryant and continuously ran to keep the house at 78 degrees.

    The bryant heat pump and air handler were replaced with a Trane Heat Pump XB-13 4TWB3042A and Hyperion XB Series 2 GAT2A0B42S31SA Air handler and XL802 thermostat.

    Now the Trane runs continuously until it reaches temperature which it seems to reach any temperature it is set at. After it reaches temperature, then it turns on for about 10 mins and off for about 10 mins and so on and so forth until late at night and then stretches out the off time with the run time at about 10 mins.

    The installer admitted to just replacing what we curently had installed, 3.5 ton for 3.5 ton. I told him about the cycling and he came out and measured the house, windows and doors to plug into a program and determine the recommended size, he called it a load test. He told me to call him today to report back how the system performed over the weekend and to let me know the results of the calculation program.

    Anyway, I am not use to the unit turning off and on so often and maybe just worring myself. In y'alls experience does this seem right or is the unit oversized? Our plan is to replace the windows, doors and roof within the next two years, will replacing these, making the house more efficent, make the unit way oversized then?

    Sorry for the long winded post, I have several thousand invested in this new system and just wanted to give as much information as possible, get as much advice/opinions as possible and have a great system that will last for years to come.

    Thanks
    Shane

  2. #2
    Join Date
    Jan 2005
    Location
    Emerald Coast
    Posts
    933
    .
    Similar sized house here would likely figure about 2 ton.

    What does his load calc say?

    And how much duct work is in this house?
    ..
    Do not attempt vast projects with
    half vast experience and ideas.
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  3. #3
    Join Date
    Jun 2012
    Location
    Folkston, GA
    Posts
    6
    He has not perofrmed the load calc yet. Said he will have it with in the next 2 to 3 days. The duct work has a main trunk line that runs down the middle of the house and short flex off the trunk line to the registers.
    Last edited by bigfoot04; 06-04-2012 at 10:14 AM. Reason: added additional information

  4. #4
    Join Date
    Sep 2009
    Location
    Arnold mo
    Posts
    3,932
    Maybe the newer units are different, but the manufacturer instructions on older units indicated the unit needed to run 15 minutes just to reach steady state, so 10 minutes on would indicate to me that it is oversized. Getting more work done on your home such as air sealing, insulating & new energy efficient windows is only going to make it worse, and maybe to the point that you start to experience mold issues.
    An answer without a question is meaningless.
    Information without understanding is useless.
    You can lead a horse to water............
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  5. #5
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,722
    Your thermostat is set to 3 CPH. Have it set to 2.
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  6. #6
    Join Date
    Sep 2009
    Location
    Arnold mo
    Posts
    3,932
    Quote Originally Posted by beenthere View Post
    Your thermostat is set to 3 CPH. Have it set to 2.
    You probably get tired of getting the same questions, but even with a CPH setting of 3, on a design condition day, wouldn't a right sized air conditioner still tend to run non-stop, rather than 10 on, 10 off? For the unit to satisfy on a design condition day in 10 minutes, wouldn't that be an indication that the unit is oversized?
    An answer without a question is meaningless.
    Information without understanding is useless.
    You can lead a horse to water............
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  7. #7
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    4,871
    If you're between the Savanna & Valdosta areas it is hot & humid; 46% to 48% at 93-F that is a lot of grains of moisture to deal with, therefore, your A/C needs to have 'extra long' runtime cycles. I'd also get the airflow CFM to 350-CFM per ton of cooling for a little colder coil & a little longer runtime.

    At 3.5-Ton it is a mere 311-sf per ton of cooling; that is ridiculous.

    Do NOT oversize; your present room thermostat should have a temperature SWING setting of 2 to 3-F to get longer runtimes!

    I'd DOWNSIZE; especially since you're also going to do some Home energy efficiency work! I'd Figure that into the sizing equation!
    Last edited by udarrell; 06-04-2012 at 02:33 PM. Reason: Clarity...

  8. #8
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    Is that all brick walls, or just brick exterior? IF it's typical 4 course brick wall counstruction, that's a lot of thermal mass so the home will heat up and cool off a LOT slower. What is the condition of the windws? Good shape or leaky? Have they ever been rebuilt/restored?

    You probably have what 8-10 windows? FOr around $100-150 each and 30-40 minutes plus a 1/2 tube of caulk, DIY installation each you can install Low-E storm windows on the exterior. and double the R value of the windows and cut the air leakage rate by maybe 2/3rds.

    FActor that into yoru load calculation along wiht adding 6-9" more instulaiton and you might be able ot go to a 1.5 ton unit depending on the load calculation. Althouhg you might be there already.

    Does you system even run 50% of the time with it's 95F and humid outside on a sunny day?

    Whatever you do, don't replace your windows. You'll never get a return on your investment and it will negatively affect the character and historical fabric of hte home. Especially in a warmer climate. People that actually love older home HATE repalcement windows.. especialyl vinyl ones... with a real passion. To most, a window and siding sales guy ranks even lower than a jahovah witness or mormon knocking on their door. My calculation show a 250 year packback vs. a low-E storm window in a colder climate. You money is better spent on geothermal, a wind turbine, solar panel or just abotu ANYTHING else.

    Old wood windows are rebuildable, new window are not maintenance free, they are disposeable. There's no such think as maintenance free of anything. It can either be serviced, or it eventually gets thrown away. Nothing lasts forever without being maintained, rebuilt or replaced.

    However, in some cases they might be beyond repair. OR, being a post war home, they might have been poor quality to begin with. Many things after WWII started to get cheaper and lower quality.. that has reached a real climax today.

    There's my window rant.

  9. #9
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,722
    Quote Originally Posted by tipsrfine View Post
    You probably get tired of getting the same questions, but even with a CPH setting of 3, on a design condition day, wouldn't a right sized air conditioner still tend to run non-stop, rather than 10 on, 10 off? For the unit to satisfy on a design condition day in 10 minutes, wouldn't that be an indication that the unit is oversized?
    If it does it on a design condition day, yes its over sized a lot. I didn't see that he said its doing 3 CPH on a design day. Could be my bad eyes.
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  10. #10
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,722
    mperluss, this is the Ask Our Pro's forum, and only Pro members that have been vetted by the AOPC may post advise here. Please apply to the AOPC today, thank you.

    You can find the rules for posting and qualifications here.


    Further infractions may result in loss of posting privileges.
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  11. #11
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    IF it's satisfied in 10 minutes on a design condition day, at CPH, then it's at 50% capacity, and you can reasonably assume it's oversized by 50%. SO in your case, 1.5 tons would like be a little small, but 2 tons just a tad large, but very close.

    IF you made significant energy efficiency improvements, you might get the heat gain low enough, especially with a lot of thermal mass, to use a 1.5 ton system.

  12. #12
    Join Date
    Aug 2010
    Location
    West Monroe, LA
    Posts
    1,529
    1100 square foot home with a (3.5) ton system. Wow!!! I am going to go out on a limb and say it is more then likely oversized. Even with rule of thumb Which I don't Belive in, you need a load cal. Preformed to determine how much heat/cooling you need.

    Either you have some major problems or they oversized it by using your current system as a reference point!! I would suggest you get his load cal. In writing. Sounds like it oversized and he is first seeing how the system will
    Work in hopes that he want have to replace!

  13. #13
    Join Date
    Jun 2012
    Location
    Folkston, GA
    Posts
    6
    Thanks for the responses and opinions fellas. First off I was wrong on my inital post, the house is 1189 sq foot.

    I do live south of Savannah, east of Waycross on the other side of the swamp right on the florida line.

    I changed the CPH from 3 to 2 as recomended and it remains off for about 20 mins now and runs for about 10-12. It was about 95 degrees yesterday when I timed the on off cycles and I am unsure of the humidity.

    It is a stick built house with gypsum board between the framing and the bricks. The windows do not appear to be leaky but could use a makeover. I've replaced several panes that were cracked. I've also had to replace several of the bottom window sashes, due to the lack of an overhang/eaves on this house, because the water runs right off the roof and splashes up on the bottom of the windows.

    I'm affraid he is going to try to navigate around replacement too. I called him yesterday and he said he has been busy but he will run the calc and get with me in a few days. I'll make sure I ask to see the report.

    If the report comes back saying it needs to be smaller and he wants to keep a happy customer and replaces the unit with say a 2.5 ton and later down the road when i add an additional room, 210 additional sq foot, to be cooled and heated too, then should I have them install a 3 ton unit which will be oversized for my current application but will even out when the new room is added? Technically speaking would a 2.5 ton be able to take on an additional 210 sq feet?

    Thanks
    Shane

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