Results 1 to 12 of 12
  1. #1
    Join Date
    Aug 2012
    Posts
    11

    New House not cooling and stuffy.

    I have a new home built as of 1 Aug 2012. It is a 4700 rambler 2340 up and 2360 in the unfinished basement. The A/C unit is a 3 ton Bryant, the furance is a 66,000 Input 54,000 Output Bryant with a 3 ton blower and the back of the house faces south. Ceilings are 9 and 10 foot, walls are R19 (2x6), R38 attic and the house is wrapped in Hardie wrap.

    The master bedroom is always stuffy and the house won't stay below 75-76 degrees when it is 92 or above outside, the thermostat is set at 74 during the day and 70 at night. I've reviewed the Manual J and Manual D as much as I can understand and it doesn't match what is installed. The Manual J is for a house rotated 180 degrees from mine and is missing several windows on the main floor, a sliding glass door, all windows in the basement and it says the furance installed is a Carrier with 88,000 Input 71,000 Output. The manual J calls for a 2.7 ton A/C.

    The Manual D says all supply branchs are run in ShMt, they are really run in F090 Air Connector. The Return Air says it is run in SJSp (I can't figure out what this is) in reality they are run in F090 Air Connector. And my return ducts are only cut about 3-5 inches high 8 inches long but have oversized grills on them to try and quiet them down.

    So my questions are:

    1) Should the opening behind the grill match the grill size or is a small opening behind a large grill ok?

    2) How important is the Manual J / D? Nothing matches and nobody seems to care.

    3) I've heard everything from the A/C unit and furnace blower are undersized, to all the duct works need to be redone.

    4) I've had the builder and HVAC company out 4 times and they just keep putting bigger grills on the returns and I was told by the owner of the HVAC that he "Can't control stuffy".

    I've paid out of my pocket for a new manual J to be done to orientant the house correctly and account for all openings, I'm waiting for the results.. I'm willing to pay for a manual D to be done but since the first one wasn't followed is this worth it? Where do you find an expert in this? Also the F090 specs seem to imply it shouldn't be used the way it is being used, which looks aweful: Sagging, compressed in half, 4-5 90 degree bends on 50 foot runs....


    Basically I'm at wits end and I'm not sure where or how to start getting a handle on this.

  2. #2
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,759
    The opening behind the grille should at least match the louver area of the grille. Most of your trouble is probably the under cut holes, and the poor duct work.
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  3. #3
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,376
    By FO90 I take it you mean flex duct. Flex duct, sized and installed improperly, can reduce system performance significantly. If your system design called for sheet metal duct and flex was substituted, I'll bet no upsizing of duct diameter was carried out. To substitute an 8" diameter of galvanized sheet metal duct with flex, one would increase the flex duct diameter by at least an inch, and also ensure the flex was stretched tightly and not kinked anywhere along its length.

    While an easy reaction is to say three tons isn't big enough for the square footage listed, the sad fact is you're probably not even getting three tons delivered to the house due to crappy ductwork and perhaps the selected supply and return grills.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  4. #4
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,637
    Stuffy? What is the temp/%RH? Fresh air ventilation?
    Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  5. #5
    Join Date
    Aug 2012
    Posts
    11
    Thanks for the replies, I think duct work is the first problem I'll try and get a handle on. F090 is listed as Air Connector by Hart & Cooley while their Flex Duct which is insulated and coated is a different classification of product. My installed flex is definately not duct by the labels left on it. Apparently the F090 Air Connector is supposed to be limited to 14' max per run.

  6. #6
    Join Date
    Aug 2012
    Posts
    11
    I live in Northern Utah and the RH today is 18%. This morning the house had cooled down to 70 degrees overnight, but it will be back up to 75/76 by 6:30 tonight. For combustion air there is a 8" pipe that goes from the basement to the attic, no other fresh air that I know of. If I put a Merv 11 it will freeze the A/C.

  7. #7
    Join Date
    Jan 2005
    Location
    southeast
    Posts
    83
    Did anyone bother to check all the operating conditions of the system or is this all an assumption as to what’s happening. Being this is a new unit you should have all the manufactures literature and you can compare actual operating conditions to unit specifications.

    What is the return static pressure at the return of the unit ?
    What is the supply static pressure in the supply leaving the coil ?
    What is the static pressure across the blower ? – across the coil ?
    This information can be used to find the actual operating airflow using manufactures information. This WILL TELL YOU if you have an airflow problem.

    What is the actual operating suction and discharge pressures?
    What is the actual suction line temperature and liquid line temperature at the outdoor unit line set. Remember these need to be accurate – probes need to be insulated from the ambient.
    What is the outdoor dry bulb – indoor wet bulb and dry bulb. While you’re at it the return and supply wet and dry bulb temperatures. These need to be as close to the unit as possible after 20 minutes of operation.

    This information can be used to see if it appears to be a capacity problem.
    Without this information your installing contractor is just guessing at the system performance. I don’t believe people spend all sorts of money on equipment and the most important step of checking the actual operating conditions and comparing to the manufacture is ignored.
    Before going any further with manuals “J”-“S”-“D” see what you got! -Find a competent individual to record reliable operating conditions and compare to manufactures information. You may find some differences there and this will be the beginning point to solve your problem.

    If you want a MERV 11 filter make sure you use a properly sized filter to prevent any excessive pressure drop in the return. The contractor should have been informed of this and constructed the return duct to accommodate it. Check the pressure drop across the filter and remember this will affect your airflow if improperly sized.

    Just the way I see it !

    Good Luck

  8. #8
    Join Date
    Aug 2012
    Posts
    11
    Quote Originally Posted by coolinman View Post
    Did anyone bother to check all the operating conditions of the system or is this all an assumption as to what’s happening. Being this is a new unit you should have all the manufactures literature and you can compare actual operating conditions to unit specifications.

    What is the return static pressure at the return of the unit ?
    What is the supply static pressure in the supply leaving the coil ?
    What is the static pressure across the blower ? – across the coil ?
    This information can be used to find the actual operating airflow using manufactures information. This WILL TELL YOU if you have an airflow problem.

    What is the actual operating suction and discharge pressures?
    What is the actual suction line temperature and liquid line temperature at the outdoor unit line set. Remember these need to be accurate – probes need to be insulated from the ambient.
    What is the outdoor dry bulb – indoor wet bulb and dry bulb. While you’re at it the return and supply wet and dry bulb temperatures. These need to be as close to the unit as possible after 20 minutes of operation.

    This information can be used to see if it appears to be a capacity problem.
    Without this information your installing contractor is just guessing at the system performance. I don’t believe people spend all sorts of money on equipment and the most important step of checking the actual operating conditions and comparing to the manufacture is ignored.
    Before going any further with manuals “J”-“S”-“D” see what you got! -Find a competent individual to record reliable operating conditions and compare to manufactures information. You may find some differences there and this will be the beginning point to solve your problem.

    If you want a MERV 11 filter make sure you use a properly sized filter to prevent any excessive pressure drop in the return. The contractor should have been informed of this and constructed the return duct to accommodate it. Check the pressure drop across the filter and remember this will affect your airflow if improperly sized.

    Just the way I see it !

    Good Luck
    Thanks I will call around and find a contractor who is willing to do those checks tomorrow as there are no residental contractors listed in Utah on the locator map. All the installer companys has checked is temperature in the house and walls and say it is fine. Oh, they did top off the outside unit once but said "it didn't really need it."

  9. #9
    Join Date
    Dec 2007
    Posts
    4,760
    If "it didn't really need it" they did you no favors doing it and may reduce performance.

  10. #10
    Join Date
    May 2008
    Location
    Central Fla.
    Posts
    311
    You need to know the "static" pressure in the ducts system, and have them bring a flow hood to check the CFM's to make sure you are pulling and pushing the proper air through the unit. Static in residential should be around ".1" and CFM's should be total of "1,200". remember your furnace is just a box that takes air in and pushes it out. You restrict either and the total air flow drops. Please let us know what is the problem.

  11. #11
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,637
    Quote Originally Posted by como View Post
    I live in Northern Utah and the RH today is 18%. This morning the house had cooled down to 70 degrees overnight, but it will be back up to 75/76 by 6:30 tonight. For combustion air there is a 8" pipe that goes from the basement to the attic, no other fresh air that I know of. If I put a Merv 11 it will freeze the A/C.
    What is the %RH inside your home?
    Regarding fresh air, you should have enough fresh air to assure an air change in 4-5 hours to keep the home fresh. The fresh air will purge the indoor pollutants and renew oxygen.
    Put a 6" duct fan on the fresh air inlet and operate 24/7 or at a minimum of when the home is occupied.
    Inside %RH should be <50%RH. Outside %RH is meaningless without temp.
    Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  12. #12
    Join Date
    Aug 2008
    Location
    Burlington , Mass
    Posts
    470
    Thanks I will call around and find a contractor who is willing to do those checks tomorrow as there are no residental contractors listed in Utah on the locator map. All the installer companys has checked is temperature in the house and walls and say it is fine. Oh, they did top off the outside unit once but said "it didn't really need it."

    You say the house is brand new, why arent you calling the installing company ? They are responsible for any problems for the first year. Get then out and obtain all the recorded info listed above.

    Keep calling till your satisfied with the service outcome.
    I'll be there when I get there and not a minute later

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