Lowe's Home Improvement
FREE PARCEL SHIPPING on Qualifying Orders

Window Air Conditioner Buying Guide

Select the right air conditioner to cool off and save on energy costs. Here's what you need to know to make the best choice for your home.

window air conditioner

Air Conditioner Terminology

Choosing the right air conditioner is easy with the right information. The first step, before you go shopping, is to learn to speak the language.

BTU: The British Thermal Unit (BTU) is the international measurement of energy. A BTU is the amount of heat required to raise 1 pound of water 1ºF Fahrenheit. In air conditioner (AC) jargon, a BTU measures the amount of heat an AC unit can remove from the room. As the BTU rating increases, so does the size, weight and cost of the AC. Room ACs are generally 5,000 to 24,000 BTU. 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 (EER) is calculated by dividing the BTU by the number of watts. The higher the EER number, the more efficient the unit should be. A higher EER-rated AC 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 to 11.5. If it's really hot where you are, go for a rating of 10 or higher.

Thermostat: The heat-sensing thermostat adjusts the temperature of the air coming from the AC unit. They can be programmable or manual. An adjustable thermostat combined with a variable-speed fan is an effective cooling machine. AC units are available with a remote control, 24-hour delay timers and digital temperature readouts.

Filter: Clean air is essential for efficient operation. Look for units with filters that can be easily cleaned or replaced.

Fan: The fan moves the air. A variable-speed fan combined with an adjustable thermostat is an effective cooling machine. Look for louvers that adjust up / down and right / left.

Chassis: The chassis is the frame that supports the main parts of an AC.

Packaged Terminal Heat Pump / Air Conditioner: This type of large heating or cooling unit, installed through the wall, is used in hotel and motel rooms.

Good to Know

ENERGY STAR® qualified appliances are environmentally friendly, energy-saving products.

Measurements to Consider

Measure the Room

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

There are lots of variables to consider when choosing a room AC: number of windows, number of people in the room, which direction the room is facing, ceiling height, etc.

The chart below can help you find the right size room air conditioner to meet your needs. You may need to adjust the BTU rating needed based on whether the room to be cooled is sunny or shaded.

Measure the Window Dimensions

Most window air conditioners are designed to fit double hung windows. Measure the inside dimensions. Take an exact measurement, not just an estimation.

Take your room dimensions and window measurements with you when you go shopping. Remember that bigger isn't better. A unit that's too large will cycle on and off too frequently, using too much energy and causing unnecessary wear on the electrical components.

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.


Have a licensed electrician connect the power to the panel box when you need to add a new circuit. Make sure your AC is properly grounded. Never alter a plug to fit your outlet.

Safety Considerations for Your Air Conditioner


How heavy is it? Get some help when carrying and installing the unit. An AC unit can easily weigh over 100 pounds.


Although newer units are much quieter than older models, be prepared for some additional noise in the room.


Follow the manufacturer's instructions carefully when installing a window unit. It's essential that the unit be stable for safety reasons. It's also essential that the unit be tightly sealed to keep the cool air inside where it belongs. Apply weather stripping as needed to prevent airflow around the unit. Put the AC in a shaded window if possible for added cooling efficiency.


AC problems can be easily avoided with simple maintenance. Keep the filter and coils clean or replace them as recommended by the manufacturer. Don't need a new AC just yet? Here's some preseason maintenance advice for your old unit:

  • Remove the inside grill. Carefully take out the foam filter. Wash in warm soapy water. If the filter's extremely dirty, wash it a few times. Rinse and allow the filter to dry before replacing. Filters that are beyond the reusable state can be inexpensively replaced.
  • Filter maintenance alone will increase your AC's efficiency. Get the most from your unit by cleaning it thoroughly. 
  • Take the unit from the window and remove the outside housing. Vacuum the interior to remove dirt, bugs and leaves. Cover electrical parts with plastic, and then wipe the interior with a damp cloth. While the unit is out of the window, take time to clean and repair the window and sill if necessary. Reassemble when dry and reinstall in the window. Reseal around the unit with new weather stripping.

Always unplug the unit before doing any maintenance.