BTU

BTU = British thermal unit, is a measure of heat, which is the amount of energy required to raise the temperature of one pound of water by one degree Fahrenheit.

<SQFT> * <Zone> = BTU required

1600 sqft * 45 / sqft = 72,000 BTU
72,000 / 12,000 = 6 Ton

SEER = Seasonal Energy Efficiency Ration

• Run an AC unit at 100% load for 1% of the time (EER_100%).
• Run an AC unit at 75% load for 42% of the time (EER_75%).
• Run an AC unit at 50% load for 45% of the time (EER_50%).
• Run an AC unit at 25% load for 12% of the time (EER_25%).

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EER = Energy Efficiency Ratio