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  1. #1

    Balancing Question

    In a 2400 Sq ft home w/ 8 rooms spread on two floors (7 on floor 1; 1 on floor 2) there is a central Central Air system (and heat pump). The entire home is a single zone w/ the thermostat in the largest room on floor 1. What is a reasonable expectation in regards to how much the temperature would vary from the room w/ the thermostat? I know that in a perfect world, the temperature would be identical in each room, but I also know that this probably not realistic. I also know that if it varies by 10 degrees from the room w/ the thermostat, there is a problem. But what I don't know is where the line of acceptability is. Is it at +/- 4 degrees from the room w/ the thermostat, +/- 3 degrees, +/- 2 degrees +/- 1 degree?


    Thanks in advance.

  2. #2
    Join Date
    Sep 2007
    Location
    wash dc metro area
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    78

    Hey Ivan

    My company's gaurantee is +/- 3 degrees with the fan left on the "on" position and +/-5 degrees in "auto". This is assuming the outdoor temp is within design limits and that the builder has the required ammount of insulation and draftstop. This is our standard for the thousands of tract homes we do each year. Custom homes we use lots of zone control systems and mini-splits to provide better comfort.

  3. #3
    I am at +/- 3 degrees. Sounds like I am OK. Just feels a little funny when I walk from one of the rooms that is +3 degrees from the thermosat to one of the ones that is -3 degrees. That 6 degree swing is very noticable.

  4. #4
    Join Date
    Jan 2008
    Posts
    2,000
    6 degree temp difference from room to room is extreme. Better sizing/ duct design is key. Tract house or not.

  5. #5
    Join Date
    Feb 2007
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    A lot depends on how tight the house is. With a good envelope, 6 degrees is high.

  6. #6
    Join Date
    Nov 2004
    Location
    SW FL
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    6,272

    Thumbs down ... not even close to a hint of Quality !

    Quote Originally Posted by fincomber569 View Post
    My company's gaurantee is +/- 3 degrees with the fan left on the "on" position and +/-5 degrees in "auto".

    This is our standard for the thousands of tract homes we do each year.
    T-stat set point = 75'F

    Do you actually mean that 70' F in one room and 80'F in another room could be considered a Guarantee?

    ... without something of QUALITY, Guarantee is definitely a misnomer.

    .................................................. ......
    guar·an·tee /ˌgærənˈti/ Pronunciation Key - Show Spelled Pronunciation[gar-uhn-tee] Pronunciation Key - Show IPA Pronunciation noun, verb, -teed, -tee·ing.

    –noun 1. a promise or assurance, esp. one in writing, that something is of specified quality, content, benefit, etc., or that it will perform satisfactorily for a given length of time: a money-back guarantee.
    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

  7. #7
    Join Date
    Dec 2006
    Posts
    85
    Just a homeowner, I heard the 3 degree difference from t-stat turning off from a tech and thought this was kind of high. I have since seen this number in numerous posts from the experts here so I consider it to be the industry standard.

    However, I have a similar situation to yours....3100 sqft home, 2 floors, one non-zoned system and have been able to achieve a difference of 1 degree at most from the thermostat at turn off. I did this by purchasing 5 thermometers from Home Depot, placing them in the same room with the thermostat to establish the difference in the thermometers from the thermostat. Then trial and error with the dampers to achieve the min/nil difference from the thermostat throughout the house. Took time (my wife thinks I am crazy) but I think it is worth it.

  8. #8
    Join Date
    Jun 2001
    Location
    Louisville, KY
    Posts
    12,181
    Quote Originally Posted by fincomber569 View Post
    My company's gaurantee is +/- 3 degrees with the fan left on the "on" position and +/-5 degrees in "auto". This is assuming the outdoor temp is within design limits and that the builder has the required ammount of insulation and draftstop. This is our standard for the thousands of tract homes we do each year. Custom homes we use lots of zone control systems and mini-splits to provide better comfort.
    You'd be ripping that from my house. 10 degree swing???? Give me a break.

    Somebody needs to learn some duct design and rotate the design on the load calc to account for change in glass orientation.
    Perhaps you should have read the instructions before calling.

  9. #9
    Join Date
    Dec 2002
    Location
    Houston,Tx.
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    15,934
    Quote Originally Posted by jrbenny View Post
    You'd be ripping that from my house. 10 degree swing???? Give me a break.

    Somebody needs to learn some duct design and rotate the design on the load calc to account for change in glass orientation.

    Well I have to give you credit JR at least you knew what he was talking about.
    __________________________________________________ _______________________
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  10. #10
    Join Date
    Feb 2007
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    18951
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    Quote Originally Posted by 7474 View Post
    Just a homeowner, I heard the 3 degree difference from t-stat turning off from a tech and thought this was kind of high. I have since seen this number in numerous posts from the experts here so I consider it to be the industry standard.

    However, I have a similar situation to yours....3100 sqft home, 2 floors, one non-zoned system and have been able to achieve a difference of 1 degree at most from the thermostat at turn off. I did this by purchasing 5 thermometers from Home Depot, placing them in the same room with the thermostat to establish the difference in the thermometers from the thermostat. Then trial and error with the dampers to achieve the min/nil difference from the thermostat throughout the house. Took time (my wife thinks I am crazy) but I think it is worth it.
    That's exceptionally good for a house of that size, but be careful not to restrict air flow too much, or the comfort you gain will not equal the damage you do.

  11. #11
    Join Date
    Dec 2006
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    85
    Quote Originally Posted by bobb25 View Post
    That's exceptionally good for a house of that size, but be careful not to restrict air flow too much, or the comfort you gain will not equal the damage you do.
    Thanks for the food for thought regarding airflow. I believe I am OK as most of the ducts remain fully open or with minimal dampering down, none are completely closed down. I guess it must be a properly designed duct system. Also, change my filter every month. Thanks again.

  12. #12
    Join Date
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    Quote Originally Posted by 7474 View Post
    Thanks for the food for thought regarding airflow. I believe I am OK as most of the ducts remain fully open or with minimal dampering down, none are completely closed down. I guess it must be a properly designed duct system. Also, change my filter every month. Thanks again.
    Yes, it does sound like your ducts are designed correctly. A room almost never needs exactly the same btus and air flow that duct sizes come in. Do you have dampers on the take offs? If so, that's the best place to close them.

    Even though I admire you tenacity, I'm still not sure your wife is incorrect.

  13. #13
    Join Date
    Dec 2006
    Posts
    85
    Quote Originally Posted by bobb25 View Post
    Yes, it does sound like your ducts are designed correctly. A room almost never needs exactly the same btus and air flow that duct sizes come in. Do you have dampers on the take offs? If so, that's the best place to close them.

    Even though I admire you tenacity, I'm still not sure your wife is incorrect.
    Yes the dampers are at the take-offs. The more time I spend on this site, the more I learn and the happier I become with my HVAC professionals (new construction).

    Almost 4 years into marriage, I am pretty sure my wife is never incorrect

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