Air Conditioner Terminology 

BTU: The British Thermal Unit (BTU) is the international measurement of energy. Here's the definition: a BTU is the amount of heat required to raise one pound of water one degree Fahrenheit. In AC jargon, BTU's measure the amount of heat an air conditioning unit can remove from the room. As the BTU rating increases, so does the size, weight and cost of the air conditioner. Room air conditioners are generally 5000 - 24,000 BTU's. Matching BTU requirements to room size is important. The room(s) won't cool efficiently if the BTU rating is too low or too high for the size of the room. 

EER: The Energy Efficiency Ratio is calculated by dividing the BTU's by the number of watts. The higher the EER number the more efficient the unit should be. A higher EER rated air conditioner will also be more expensive, so decide if the higher price tag is worth the energy savings you may be getting. The ratings range from 8 - 11.5. If it's really hot where you are, go for a rating of 10 or higher. 

Chassis: A fixed chassis is characteristic of a lighter weight, smaller unit that's easy to remove for winterization. A slide out chassis is found on larger, heavier models. The unit slides out easily for maintenance.

Measure the Room 

Determine the square footage of the room (length x width).  

There are a lot of variables to consider when choosing an air conditioning unit. The number of windows, family size, ceiling height, and which direction the room is facing are all factors to take into consideration when deciding what size is best.  

This is an estimate on the right size air conditioner depending on the size of room:  

• 100 - 300 square feet: 5000 - 7000 BTU’s per hour 
• 300 - 500 sq. ft.: 8000 - 12,000 BTU’s per hour 
• 500 - 1000 sq. ft: 14,000 - 18,000 BTU’s per hour  
  
  

Note: Bigger is not better. A unit that is too large will cycle on and off too frequently, using too much energy and causing unnecessary wear on the electrical components.  

Measuring the Window 

Most window air conditioners are designed to fit double-hung windows. Measure the inside dimensions (the lower part of the window that raises). Take an exact measurement, not just an estimate. 

Take your room dimensions and window measurements with you when you go shopping. 

Check the Power Supply 

What kind of plug does the unit have? What kind of plug is your wall outlet? Make sure the circuit can handle the operation of the unit. Smaller ones work with a standard 115-volt outlet. Larger 115-volt units may need a dedicated circuit. The largest AC units require a 230/208-volt circuit.