Lowe's Home Improvement

Window Air Conditioner Buying Guide

A window air conditioner cools you off and can help you manage energy costs. This guide helps you learn about different types and how to choose one for your home.

Window Air Conditioner Buying Guide

Window Air Conditioner Operation

A window air conditioner, also known as a window A/C or a room air conditioner, is designed to cool a single room and can be a good, easy-to-install option if a central air conditioning system is not practical or if you want to cool a single room rather than the whole house.

Depending on the model, a window air conditioner can operate in different modes. The cooling mode takes in room air, cools it and directs it back into the room. Some models allow you to select from several preset cooling levels; the air conditioner cools at the selected level until you change the setting or turn the unit off. Other models let you set a desired temperature for the unit to maintain. The air conditioner operates until it senses that the air is at the desired temperature and then cycles off, cycling back on when the temperature rises above the specified setting. A fan-only mode uses less energy because it doesn't provide cooling. The appliance simply circulates and filters the room air. Some window air conditioners have a heating mode. As with the cooling function, you set the desired temperature and the heating system cycles on and off to maintain it.


Follow the air conditioner manufacturer's instructions for safety, installation and operation.

Choosing a Window Air Conditioner

The right air conditioner helps you cool a room efficiently. An undersize unit won't cool adequately while one that's too large will not remove enough humidity, leaving the air feeling damp. To find the proper air conditioner, determine the square footage of the room you want to cool by multiplying the room length by its width. You also need to know the air conditioner's BTU (British Thermal Unit) rating, which indicates the amount of heat it can remove from a room. A higher number means more cooling power for a larger room. Compare your room size to the BTU rating:

  • 150 to 350 sq ft: look for a 5,000- to 8,000-BTU unit
  • 350 to 550 sq ft: look for an 8,000- to 12,000-BTU unit
  • 550 to 1,050 sq ft: look for a 12,000- to 18,500-BTU unit
  • 1,050 to 1,600 sq ft: look for an 18,500- to 25,000-BTU unit

Consider conditions that may reduce the cooling need — the room is always shaded, for example — and those that may increase it — the room receives a lot of direct sunlight or regularly has more than a couple of occupants. Keep in mind that as the BTU rating increases, the size and weight of the air conditioner does as well.

Good to Know

EER stands for Energy Efficiency Ratio. A higher EER indicates a more efficient air conditioner.

Window Air Conditioner Considerations

Most window air conditioners are designed to fit double-hung windows, which have a sash you can raise or lower. Measure the inside dimensions of the installation window carefully to make sure you find a model that fits. Don't rely on estimates. Here are some other things to think about:

  • Window air conditioners are heavy. Enlist a helper when carrying and installing the unit.
  • Installing the air conditioner in a shaded window will help it operate more efficiently. A window facing north will be in shade most of the day
  • The window you select for installation needs a suitable power outlet nearby. The manufacturer may specify that you plug the device directly into the outlet with no extension cord.
  • The circuit the outlet is on must be able handle the electrical load of the air conditioner.
  • Different models have different plug configurations. Make sure the air conditioner you select is compatible with your outlet. Check the product packaging for the plug design.

Never alter an electrical plug. Contact a licensed electrician if you have any doubts or questions about the circuit or outlet or if work such as installation of a new circuit or plug is necessary.

Window Air Conditioner Features

Window Air Conditioner with Electronic Controls.
  • A programmable timer lets you set the unit to turn on and off at specific times, helping you reduce energy consumption by operating the air conditioner only when it's needed.
  • Mechanical controls allow you to adjust fan speed and cooling level and are simple to operate. Electronic controls give you more flexibility, allowing you to set a specific temperature for the air conditioner to maintain.
  • A sleep setting increases the specified temperature incrementally over a period of time before returning to the original setting several hours later. This feature keeps the air conditioner from maintaining an unnecessarily cool temperature in a room where the occupants are sleeping. It also reduces noise since the unit is running less frequently.
  • An electronic ionizer helps the air conditioner more effectively remove impurities such as pollen from the air.
  • Venting options let you choose between recirculating room air, pulling outside air into the room and exhausting room air to the outside.
  • Air conditioners remove humidity from the air as they cool it. Different models have different dehumidification capabilities. Look for a rating measured in pints and ounces of moisture removed per hour.
  • A remote control adds convenience — you can adjust settings and turn the air conditioner on and off from across the room. Some remotes can function as temperature sensors, activating the air conditioner when the air around the remote is warmer than the temperature specified in the settings.
  • A filter alert lets you know when the air filter needs cleaning.
  • An extra-long cord helps you reach a power outlet.

Window Air Conditioner Operating Tips

There are several things you can do to help a window air conditioner cool your home:

  • Make sure the air can flow freely around the air conditioner. Outside of the home, keep the unit clear of obstructions such as shrubbery. Inside, make sure obstructions such as window treatments and furniture are clear of the unit.
  • Help keep the cool air in the room by closing fireplace dampers and floor or wall registers. Reopen them when using the fireplace or home heating or cooling system.
  • Consider closing window treatments when it's sunny outside, but remember to avoid blocking the air flow around the air conditioner.
  • Keeping the exterior of the room you're cooling shaded will help the air conditioner keep you cool, but make sure that airflow around the exterior of the unit is not restricted by trees, shrubs or other obstructions.
  • Maintain correct insulation and weatherstripping throughout your home. See Install Insulation to learn about insulating your home. Read Weather Strip Your Doors and Weather Strip Your Windows to learn about sealing air leaks in your home.
  • When possible, reduce the workload of the air conditioner by using appliances such as dishwashers, ranges and dryers during the cool hours of the day.
  • Use accessories such as weatherstripping and foam side panels to help you seal and insulate the area around the air conditioner.

Window Air Conditioner Maintenance

Simple maintenance helps keep an air conditioner operating efficiently and can maximize its lifespan. Unplug the air conditioner before performing maintenance. Here are some common procedures:

  • Check and clean the air filter regularly as specified by the manufacturer. A dirty filter makes the air conditioner work harder, reducing efficiency. You may be able to vacuum the filter or wash it with water and a mild detergent, such as dishwashing liquid. Allow it to dry before reinstalling.
  • Wipe down the cabinet with a damp cloth and mild detergent as needed. Keep water away from the control panel.
  • Prepare the unit for storage over the winter according to the manufacturer's instructions.

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To learn about ENERGY STAR and room air conditioners, visit the ENERGY STAR room air conditioners page.

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