Is there a formula to properly size a window or in-the-wall air conditioner (how many BTUs are needed) to cool your room correctly?
Yes, there is a formula to calculate the proper amount of BTUs needed to cool a room, however it is long and complex.
Below is the explanation of the easier "W H I L E" formula.
The "W" stands for the Width of the room;
The "H" stands for the Height,
The "I" stands for the Insulation value in your walls,
The "L" stands for the Length of the room
The "E" stands for the Exposure. In other words, the direction your longest outside wall in that room is facing.
Measure out your room's Width, Height and Length.
For "I" use the number 10 for well-insulated walls or the number 18 for poorly-insulated walls.
A wall with R-11 insulation or less is poor.
For "E" use the number 16 if the longest outside wall is facing North; 17 if facing East; 18 if South; 20 if facing West.
Multiply W x H x I x L x E and divide by 60.
Your answer is in BTU's.
Buy a unit closest to this BTU answer and a model only with the Highest E.E.R.
The following factors are not included with this "WHILE" formula:
Body heat, an upstairs room with a Flat roof or uninsulated attic and window exposure.
Be cautious with the calculations some sales people may do on the sales floor for you. The calculated answer sometimes seems to be exactly right for the air conditioning units they have most in stock.
What is a BTU?
B.T.U. stands for British thermal unit, the quantity of heat (energy) required to raise the temperature of one pound of water one degree Fahrenheit.
Updated Blog Post - From EnergyHotwire.com to GoingTrueGreen.com
Bill Lauto, at GoingTrueGreen.com
International Sustainability and Energy Consultant
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