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  1. #1
    Join Date
    Jul 2008
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    AC problems and issues

    Hello all,

    The forum monster ate my first attempt to post. So, lets try again.

    I have just had a new house built in Middle Tennessee. Pretty standard "L' house. one main floor, garage coming off the front of the house, and a bonus room over the garage.

    Main floor is 1475sq ft with 9' ceilings, no vaulted. Bonus room is 450sq ft. Bonus room was built by extending the garage walls upwards about 5-6 feet. Not your standard 4foot knee walls. This gave us more useable area, more volume.

    Front of the house (front of garage) face East. Across the street is another house and behind it is woods. Trees go up about 3-4 stories. So, lots of morning shade from trees. They are about 225-250 feet away.

    Back of house faces full west. Right side is north and open to a vacant lot, left side is South and points to another house 14 feet away.

    Air unit is split between outside and attic. Fan/evaporator outside, main unit in the attic. I am not positive, but I think we have a 3 ton unit. Thats what they "told" us they were going to install, but I have yet to verify that. Going to do that first thing getting home today.

    Attic roof has 5 passive vents on the west face, 3 on the north face of bonus room roof. looks like standard soffits(?) run the eave area of the house.

    Before the move in we noticed that the AC unit was having difficulty cooling the house on bright sunny afternoons. We worked in the house several weekends during the end of the build and noticed that the house would not cool below 81. We sat there one Sat and at 2pm, it was 81 in the front room. we set the thermostat to 68. 5 hours later the house was at 78.

    Builder had the HVAC guy check the system. all charged and perfect working order. They checked it in the early AM when it was cool. AC would cool the house very quickly. However, they only came back once when it was 80+ in the front room and AC was not cooling.

    I checked the attic heat during this time. Attic door is in the bonus room, very close to east face of roof. On birght sunny, 90 degree days, attic temp at the door was 130. Figure it was hotter than that out in the main attic space. If the attic temp was above 105, the AC had problems cooling the main floor.

    The attic ducting has a main line that runs the lenght of the roof peak and connects to the AC unit in the attic. From that line, duct runs go down to the room vents. The return register is in a hallway off the main room, about 5 feet from the thermostat

    I also put a temp guage at the air vents. the "main area" of the house has the living room and kitchen. Big open area that is about 30x30 approx. there are 3 vents feeding this area. 2 on the west wall, one on the east. When the ac is working, the temp of the air at the west wall vents is 68. Therm is set for 72. Temp of the air on the east wall is 64.

    If I close of the bedroom on the east (Front) of the house while the ac is working, that room drops to at least 70.

    Builder says that HVAC guy says once we get moved in, blinds up, etc, the house will cool better. But, what we are seeing is the same issue.

    ON bright sunny days, the west face of the roof gets sunlight for almost 8 hours. Temp will soar into the 125+ in the attic. We got home at 6pm last night and the thermostat was at 81 and the setting was for 77. House felt cool in the kitchen. Once the sun went down, in a matter of about 30mins the house cooled off and the AC shut down.

    So, over a period of a couple of weeks I"ve monitored attic temps. If its a bright sunny day that has the attic up to 120+, odds are we come home and the AC is running, trying to cool an 80 degree down to 77. Bonus room will be at about 75. On days where it is cloudy or cool, we come home and all is well in the main room. AC is not running, Thermostat and temp setting agree. However, bonus room will be at 78-80.

    This morning I get up, and the main room is 75, thermostat stillset for 77. Bonus room is at 81. No idea where that heat is coming from. Suspect it is feeding up from the garage. A check of the attic shows that is at 68.

    So, I'm not sure what is going on and why we are having so many issues. My gut is telling me that 1) their is insufficent venting of the attic heat, 2) The bonus room should have been given its own thermostat and unit and 3) the unit is either not a 3-ton (thus too small) or is not setup correctly. At install, teh builder said his standard unit is 2.5 ton, but he was adding .5 ton to the unit to handle the bonus room.

    So, they are going to come and and do a complete recheck of the AC setup, the design, etc. They want to know put in a gable vent at the front of the bonus room. They bricked up the front from garage door to roof peak. A whole had been cut for avent, but it was bricked over.

    I'm suspecting that we need gable vents at the north/south ends of the roof, in order to get soem cross flow venting in the attic. I also thin they need to add turbine vents to a couple of the passive vent holes.

    So, what shoudl I be listening for when they come in to do this respect. Am I missing something in this setup. I was also worried that all of that ducting running along the west roof plane was heating up and not putting out cold enough air.

    Any thoughts or things to look for is greatly appreciated.

    Last edited by dcsobob; 07-18-2008 at 04:38 PM.

  2. #2
    Join Date
    Jan 2004
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    Edit out your email addy. They are not allowed in post.
    You can put it in your bio.

    Read the mod number off your outdoor unit and post it. Also the brand.

    It may be that your attic needs more ventilation.

    How much insulation is in your attic. Check it. If its blown in. Somethimes, they fluff it too much.

    What insulation value does the duct have. R6, or R8.
    Contractor locator map


    How many times must one fix something before it is fixed?

  3. #3
    Join Date
    Jun 2008
    phoenix az
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    this does sound like an interesting problem. i dont have much time, but i'll give you some advice for things the a/c contractor needs to check. first thing they need to check, is to make sure the outdoor unit is not installed under a low overhang or to close to walls. also, your static pressure in your duct work needs checked to ensure you have enough airflow, particularly return air flow. you did not specify if the duct work in the attic is metal, duct board of a spaghetti mess of flex duct. i see all to often with flex duct installs, the return duct from the can to the unit is so badly kinked somewhere in the rafters the it kills airflow. sorry but i'm out of time and gotta go, but i hope this helps somewhat.

  4. #4
    Join Date
    Jul 2008
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    Thread Starter

    AC updated info

    Can't give you the type fo duct work. When I look at it it is just big shinny flex tubes, But, its not metal. It looksto be the metal ducts wrapped in a foil-type wrappping. I am not sure of the R-factor but the HVAC guy said he "overwrapped" them to ensure they do not heat up inside.

    The unit sits outside on a concrete pad and is about 2-3 feet from the house. The over hang is only about 18", so the unit does not sit under it.

    I could not see any kinks in the duct work. All the piping looked straight and good when I have checked.

    The unit is a Goodman with a gas furnace as well. I'll grab the model number

    The requirement is 24" but they blew in about 26-27. I spot checked the depth in some places. I have two large trunks in the attic. I suspect one goes to the return, and the other feeding the room vents. All duct work is open to the attic in that there is no insulation blown on top of it. its around the register return trunk, but all of the rest of the duct work is strapped to the rafters. The Main trunk is runningon a set of cross members at teh apex of the roof, so the feed lines for the rooms come off of it and run down to the ducts, strapped to the rafters.

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