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Air Conditioner Sizing & Buying Guide

A comprehensive air conditioner guide that will give you all the information you need when shopping for a new air conditioner.

Getting Started

Take the edge off of smoldering summer heat with an air conditioner that perfectly fits in your space. This buying guide is your complete reference for anything and everything dealing with air conditioners. BTUs, Voltage, Styles, and Features are covered in detail, to help you pick out the right air conditioner for your home.


When picking out an air conditioner, it's important to choose a unit with the proper cooling capacity (measured in British Thermal Units, or BTUs) for the room it will be cooling. Air conditioners with either too little power or too much power can lead to problems further down the road.

An underpowered unit will struggle to cool a room effectively, running constantly and using excess energy. To avoid this, many people will simply buy the most powerful air conditioner that they can afford, but that will also have unwanted effects. Air conditioners are designed to remove both heat and humidity from a room.

An air conditioner that is too large for a room will cool that room too quickly and then shut off without removing the humidity, giving the air a damp, uncomfortable feel. So the first step, when shopping for a new air conditioner, is to measure the room or space that it will be cooling. This will provide the necessary information needed, in order to choose an appropriately-sized unit.

To do this, determine the square footage of the room by multiplying the length by the width. Below is a handy chart that will help you find the right size room air conditioner to meet your needs.

Once you have your base BTU requirement, the following adjustments are suggested:

Heavy Sun Exposure

For rooms with heavy sun exposure, increase the capacity by 10%

Little to No Sun Exposure

For rooms that get little to no sun, decrease the capacity by 10%

How Many People Occupy the Space?

If the room is regularly occupied by more than two people, add 600 BTUs for each additional person.

Is the AC Going to Be near the Kitchen?

If your AC will be used in the kitchen, increase the capacity by 4,000 BTUs.

What To Know Before You Buy An Air Conditioner


The next step is to determine which type of air conditioner you need to purchase. This will be determined by what type of windows you have, or if you have a room designed to accommodate a wall air conditioner.

Window Air Conditioners

Window Air Conditioners
These are the most common types of portable air conditioners, and are made for windows that slide up and down. The AC sits on your window sill and vents hot air outside. Moisture pulled from the air in your room is also released outside. The AC may be installed permanently, or in a way that makes it easy to remove for the winter. Additional accessories can also be purchased to assist in ensuring a perfect fit for any window.

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Casement Air Conditioners

Casement Air Conditioners
A casement air conditioning unit is designed specifically for windows that swing out to the side (usually with a hand crank) or slide open sideways.

Shop Casement Air Conditioners

Portable Air Conditioners

Portablesement Air Conditioners
Intended for rooms with windows that cannot accommodate mounting a full AC unit, or for those who want the ability to move the AC unit from room to room. A portable air conditioner is placed on the floor and uses a flexible hose to vent hot air outside. The venting hose can usually fit through a small space, such as the center vent often found in basement glass-block windows.

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Wall Air Conditioners

Wall Air Conditioners
These are installed through the wall of a building in a designated opening. Wall Air Conditioners require a sleeve in order to be properly installed.

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Central Air Conditioning Systems

Central Air Conditioning Systems
Central Air Conditioning Systems consist of one main unit that pumps cool air through ducting that runs throughout a building, eliminating the need for separate AC units in each room. If you are looking to do away with portable or window air conditioners, Abt is licensed to install central air systems. This service is only for our Chicagoland customers. Individual homes will need to be estimated before choosing and installing a central air conditioning system.

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Other Things To Consider

Once you've decided which type and size AC unit to buy, you can further narrow down your selection based on features specific to individual models. Features like AC controls, remote controls, as well as integrated air filters are all key things to consider.

Ability to Direct Air Flow

Air conditioners usually have adjustable louvers that allow you to direct airflow vertically or horizontally. Consider your room layout, and make sure to select a model that allows you to direct the airflow to the areas of your room where cooling will be most needed.


The most basic air conditioning units will have very simple controls: a knob for temperature and a knob for fan power. These models are great for getting a blast of cold air into a room, but don't allow for subtle climate controls. More advanced models are equipped with digital displays that let you set a more accurate target temperature, which typically can be programmed to go on or off at certain times. Some have sophisticated energy saving modes as well.

Another option to consider are models with a remote control. Remote controls make temperature adjustments easy from anywhere in the room..


A few models provide heat as well as AC. This is a great option for those times between seasons when it's a little chilly, but not cold enough to turn your home's furnace on.

What's my plug type and what voltage do I need?

Your plug type will let you know the voltage and amperage requirements of your new AC. Make sure your new AC Unit matches your existing electrical requirements. Attempting to plug your AC unit into an outlet with a different plug type or voltage can be very dangerous. Below is a chart illustrating plug types and their corresponding electrical information.

Voltage and Amperage