How To Install an Air Conditioner

How to install an air conditioner will depend on the type you have or the type you decide to buy. This year, instead of waiting until it gets so hot you can’t stand it, install an air conditioner while the weather is still mild. Lugging that big box out of the attic or home from the store in 100 degree temperatures is nobody’s idea of a good time. By getting it done early, you can relax and enjoy the cool air inside when temperatures soar outside.

Measuring Space

It is important to measure the space you are cooling to ensure the unit you have is adequate to do the job. An air conditioner that is too small will never give you the comfortable temperatures you want and will cost you a fortune in cooling costs because it will be running all the time. You should also understand that air conditioners also pull moisture out of the air, dehumidifying the space. If you have an air conditioner that is too small for the room, the air will be cool and clammy. This is no more pleasant than hot and sweaty, so get the right air conditioner for the job.

Calculating Square Footage

When measuring the space for your air conditioner, understand that you will need about 12,000 BTUs to cool an area of 1,000 square feet. To get the square footage of your space, break up the room into square or rectangular shaped areas that you can measure and then add up. Area is obtained by multiplying the room section’s width by its length. Add up the room sections to come up with your total square footage. If you have high ceilings, add 10 percent to your number.


Luckily, there are websites out there that make it easy to calculate what you need. Once you know your square footage, you can use the Good Housekeeping air condition calculator to determine the right capacity air conditioner. You can also use this very in-depth air conditioner guide at Consumer Reports to help you measure the space and determine the right size air conditioner. Otherwise, you can just do an Internet search for “AC BTU Chart” to look up the right BTUs for your space.

What Kind of Air Conditioner?

The next steps depend on the type of air conditioner you have. Standard window and casement air conditioners need to be lifted and mounted. Portable air conditioners rest on the floor and you only need to install the exhaust pipe into the window.

Window Air Conditioners

The standard window air conditioner is a self-contained unit, made to fit in a standard window that opens by sliding up or down. You can also get a window air conditioner called a casement air conditioner for non-standard windows, such as those that open side-to-side or those that are very narrow.

Choose a Location

Choose a window with an outlet nearby so you can plug in the air conditioner. Also check that the window sill is in good condition to support the unit. Measure the opening (twice!) to be sure you are using an air conditioner that fits properly. You will need these numbers while shopping to make sure you buy one that fits the opening.

Window air conditioners are installed in the window so that they rest on the sill. The unit is supported by brackets attached to the outside of the house or on sill-mounted supports. These brackets hold the air conditioner at a downward-sloping angle so that water can drain out of the unit. All of the hardware you need will be included with a new air conditioner. If you are reinstalling an older unit, check to be sure you still have the old brackets. Otherwise, you will need to run out and get some new ones.

Essentially, you need to install support brackets first. Older units will have brackets that are installed on the exterior of the house, just below the window. Your unit might also have sill supports that the unit can rest on. In either case, you will need to adjust the angle of the brackets once they are installed to make sure the air conditioner drains properly once it is installed.

The next step is the hardest part, especially if you have a large unit. You will need to open the window as wide as it will go and lift the air conditioner into place. Get help for this part of the job, even if the air conditioner is relatively light. Many air conditioners have been dropped and destroyed by those trying to do the job themselves. Not only this, a dropped air conditioner could seriously injure anyone unlucky enough to be walking underneath at the time.

Once the air conditioner is in place, it will catch on the brackets. Hold onto the unit and pull the sash down onto the unit. You then need to screw the air conditioner into the sill of the window. If you have lost these screws, go get new ones! This is an important safety feature. Many a sleepy wanderer has opened a window in the dark only to hear a loud crash below as the air conditioner falls from the window.

Once the air conditioner is secured with screws, pull out the extension on either side of the unit. Place foam insulating strips along any gaps. You should also take the time to caulk around the unit outside. Many homeowners skip this step, wasting a lot of money on cooling costs.

Portable Air Conditioners

Gaining in popularity over the last few years, portable air conditioners are units that remain on the floor within a space and can often be rolled on wheels.   These units operate like small refrigerators and dehumidifiers, built into one unit. Like a dehumidifier, the unit will need to be emptied periodically as it fills up with water. Unfortunately, these units do not cool as well as window air conditioners and often need to be purchased at double the capacity in BTUs. The units with two hoses often perform better.

Portable units are more expensive than window air conditioners, but they are easier for a single person to install and offer more flexibility for installation. These units can be installed almost anywhere. You only need to install the two vent hoses in a window so that one can draw in air and the other can vent it. You only need to install a plastic kit along the window sill and hooking up the hoses.