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  1. #1
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    Jul 2019
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    Calculation for size of unit needed

    I may need to install a larger capacity unit to serve a basement that is freshly finished with new ductwork and return. When the unite was originally installed the HVAC was designed and sized for home without the finished basement.

    What is the quickest simplest way to calculate how much more cooling capacity-CFM I will need by using cubic feet window r value etc?

    I am a former HVAC tech and I remember learning this in college but we did it all in a software program.

  2. #2
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
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    Basements typically provide free cooling during most of the cooling season. The biggest problem is the latent cooling load of a basement. This is usually best handled by using a premium dehumidifier which adds a small amount of heat to a space that tends to run on the cool side with needing some latent heat removal.
    Where the home located? What is the temperature in the basement nights/days?
    Keep us posted.
    Regards Teddy Bear
    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"

  3. #3
    Join Date
    Aug 2002
    Location
    Southold, NY
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    Small Mini Heat Pump and good Dehumidifier!

  4. #4
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    Jul 2019
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    Thread Starter
    Thanks for your replies. Good advice. I forgot the basement would not calculate the same way as the rest of the house. Just out of curiosity is there any quick easy way to size a house for capacity. I have an old manual J from college but looking back over it it looks complicated. Its hard to believe I passed that exam back in the day lol.

  5. #5
    Join Date
    Aug 2002
    Location
    Southold, NY
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    There are on line sources that will do it for a fee!

  6. #6
    Join Date
    Oct 2011
    Location
    Gladstone, Oregon (Portland)
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  7. #7
    Join Date
    Jan 2004
    Location
    PA
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    Your unit is probably over sized for the house already. So finishing the basement won't require increasing its size.

    However, a basement's needs even when finished is never the same as the first or higher floors. So at min, will require the system to be zoned. Or its own system installed.
    Contractor locator map

    How-to-apply-for-Professional

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

  8. #8
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    9,076
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    Confused INITIAL THOUGHTS

    Quote Originally Posted by Jmeador View Post

    Thanks for your replies. Good advice.

    I forgot the basement would not calculate the same way as the rest of the house.
    Just out of curiosity is there any quick easy way to size a house for capacity.
    … Yes, RULE-OF-THUMB for MODERN Construction
    __________ if you wish to have an accuracy of ONLY +/- 32%


    I have an old manual J from college but looking back over it, it looks complicated.

    Its hard to believe I passed that exam back in the day lol.
    SEND ME details of your residence and I can get you started.
    It is not complicated in concept.
    However, it requires a LOT OF DETAILS [ TIME ] to develop an Accurate calculation Model.
    My GMAIL Address: racingdan11

    ATTACHMENT
    ___ MY CALC .. INPUT FORM … LOCATION --- BUILT

    EXAMPLE - MANUAL J INTRO
    The majority of calcs are performed based on drawings.

    Only 19 pieces of information are needed for a BLOCK LOAD ( per floor or Whole House)

    ATTACHMENT
    _____ Shaded items on
    _ _ _ LINES 5, 8, 11, 12, 13, 15, 16, 18, 19, 21 - 26, 30, 35, 41, 42

    Location - with street address,
    _ I can see the front/ side exterior of your house
    _ + I can measure it

    + ZIP: _ _ _ _ _
    _ _ _ _ _ for Heating Degree Days (HDD) __ Operating $$
    _______ for Cooling Degree Days (CDD)
    _______ for Design Temperatures ___ ASHRAE 1%

    _ _ _ … … _ _ _

    ___ AGE: good-to-know to estimate Insulation and Infiltration

    Size: Perimeter & Total Floor Area
    Wall Height
    # of Floors

    Wall R-Value

    Ceiling R-Value

    Floor R-value

    Windows:
    SHGC & U-Value
    Orientation – Square Feet each direction
    North __ Sq Ft
    South
    East
    West

    Number of bedrooms

    Infiltration - A.C.H. Natural
    _____ Blower Door Test results

    Fuel Costs, AS Applicable
    Oil $ _. _ _ gallon

    Natural Gas $ 0._ _ / Therm
    Electricity $ 0.1_ _ / kw-hr
    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

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