# Thread: Calculation for size of unit needed

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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. 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

3. Small Mini Heat Pump and good Dehumidifier!

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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. There are on line sources that will do it for a fee!

6. 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.

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## INITIAL THOUGHTS

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.

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
_ _ _ LINES 5, 8, 11, 12, 13, 15, 16, 18, 19, 21 - 26, 30, 35, 41, 42

_ 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

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