How does a window air conditioner unit work?

A window air conditioner, also known as a room air conditioner, functions like a mini-fridge: The unit extracts heat and moisture from a room as it circulates cooler air, much like a refrigerator does. The exact cooling process is similar to that of a pump using a chemical substance that transitions between liquid and gaseous states with a change in pressure. As the substance, called a refrigerant, moves from a liquid to a gas, it absorbs and releases heat from its surroundings.The refrigerant is contained in coils. The cooling process takes place because these coils are cooler than the air inside the room. The air conditioner pulls warmer air from the room into the unit; the cooling coils condense water from the air, and then the unit sends the cooled air back into the room.As the cooling coils remove heat, they also get hot. This is why the air conditioner blows hot air out the back of the unit, into the outdoors. In addition to removing heat, a window air conditioner also helps dehumidify a room.Typically, you’ll see a thermostat in the back of the unit to help it keep the room at the desired temperature. The air conditioner will turn off when the room reaches the temperature you’ve set.

What are the advantages of a window air conditioner unit?

Affordable: Window AC units are generally more affordable than other types of air conditioners, so you can enjoy cool comfort without spending a lot of money.,Targeted cooling: If you don’t want to cool an entire house, window AC units let you only cool the rooms you use most. Additionally, by precisely cooling only the rooms you want to cool, you can save on energy costs.,Compact size: By sizing the unit to the room you want to cool, you ensure that it cools the space you want it to without wasting energy.,Installation flexibility: You can place a window AC unit in just about any room you want to cool. An individual can install and remove it in cooler weather — no professional needed.,Low maintenance: Window ACs don’t require much upkeep and are easy to control.

What are the drawbacks of a window air conditioner unit?

Danger/security threat: If you install a window AC unit on the ground floor, you could create a vulnerable area — an intruder could remove it to get access to your home. On higher floors, AC units could fall and cause damage or injury. Make sure you’ve sized and/or reinforced the window properly before installing a unit.,Inefficient: Window AC units are not efficient for cooling larger homes and, being room-specific, lead to “dead zones” in hallways, foyers and other connective spaces. While individually cheaper, window units in multiple rooms tend to be more expensive than a central air conditioning system.,Drainage problems: Window AC units remove water from the air and drip it outside of the window. This could prove to be a problem if you don’t have a good drainage system underneath.,Unaesthetic: Window AC units are not unobtrusive: They are visible from both inside the room and the outside of the building. Additionally, they may block views and light from the window.

What type of air conditioner works best for different home settings?

There’s no single type of air conditioning system that works for every home, but some units and solutions are better for specific situations.Central air conditioning systems distribute cooled air through ductwork, making them a perfect fit for big houses or single-floor homes.Ductless mini-split air conditioners (which can have as many as four wall-mounted indoor units) are a great option for open floor plans or multi-room spaces, because they can direct cooled air to specific areas of the home. They have separate evaporators and fans for each room, so you can place them in areas where you spend the most time inside.Window, portable and floor-mounted AC units are all smaller and designed to cool specific rooms. Portable air conditioners offer mobility, so you can move these units from room to room based on where you need air conditioning most. One variety of window ACs, the saddle air conditioner, is designed to be installed at the bottom of a window, making it ideal for maintaining a nice view or enjoying sunlight.

How to install an air conditioner

Written by

Troy Segal,

Edited by

Suzanne De Vita

Published on October 30, 2023 | 7 min read

Bankrate is always editorially independent.

Our writers and editors used an in-house natural language generation platform to assist with portions of this article, allowing them to focus on adding information that is uniquely helpful. The article was reviewed, fact-checked and edited by our editorial staff prior to publication.

Key takeaways

Window AC units are generally more affordable and can be installed by two people in two hours.
DIY-ing the job saves you an installation bill of $140 to $500, depending on the type of unit.
You can leave the unit in year-round, but that’ll prevent you from opening and closing the window.

There are three main ways to cool your home: central air conditioning, window AC units and portable air conditioners. If you live in a place that doesn’t have central air conditioning, a window unit may be the way to go. And you can install such an air conditioner yourself, even if you’re not the most experienced DIY-er: It mainly takes a buddy, some basic tools and a little heavy lifting. Here’s how.

How to install an air conditioner

Before you purchase and install a window air conditioner, you want to know what type of window you have: standard windows that open by lifting them up, slider windows that open to the side or casement windows that crank open. Second, you need to measure the opening of your window. Finally, make sure you have power outlets nearby to plug in the unit.

What do you need for installation?

You only need a few basic tools and materials for window air conditioning installation. In addition to the unit itself, you need:

Tape measure
Drill
L-shaped bracket
Screwdriver
Screws
AC foam insulation weather strip
Scissors
Support bracket (optional)

AC installation steps

Allow for enough time: If this is your first time installing a window air conditioner, it may take longer than you think. It’s best to be on the safe side and plan for about two hours.
Prep the window: Make sure there’s no wood rot damage around the window. (If you see signs — significant stains, bubbling/peeling paint, mold spots or sagging — you should scrape it away and apply wood hardener first.) Remove any debris that may be on the window frame, and the storm window or screen if it could interfere with your unit. If you don’t think your window can handle the weight of the air conditioner, you may need to attach a support bracket. This will transfer some of the unit’s weight off the window and reduce the chance of damage.
Prep the air conditioner: Slide the accordion panels on each side of the air conditioner. These are adjustable and can be opened or closed so the air conditioning unit and the accordion panels fill up the window’s width.
Place the air conditioner: Put the air conditioning unit in the open window and rest it either on the bottom of the window frame or the support bracket (if you installed one). Due to the heaviness of window air conditioning units, it will take two people to complete this step. Then center the unit in the opening.
Secure the air conditioner: Lower the window to the top of the unit, so the unit’s flange, or upper lip, is in front of the window sash. Use screws to attach the unit’s flange to the sash. Using additional screws, attach an L-shaped bracket to connect the bottom window sash to the top window sash. This will prevent the window from accidentally opening.
Attach the accordion panels: Pull each accordion panel out to the edge of the window. Screw them into the window sash so they stay in place.
Add insulation: Many window air conditioners come with a foam insulation strip. If yours is old or you can’t find it, you can purchase one at most hardware stores. Cut the strip so it is as wide as the window. Place it between the upper and lower window sash so it fills the gap.

Once you’ve followed these seven steps, your window air conditioner is ready to be plugged in and turned on.

How big of an AC unit do I need?

A window air conditioner’s cooling capacity is measured in British thermal units (BTUs). The ideal BTU for a room depends on its size.

Area to be cooled (square feet)	Capacity needed (BTUs per hour)
100 up to 150	5,000
150 up to 250	6,000
250 up to 300	7,000
300 up to 350	8,000
350 up to 400	9,000
400 up to 450	10,000
450 up to 550	12,000
550 up to 700	14,000
700 up to 1,000	18,000

Source: EnergyStar

Temporary vs. permanent AC installation

Window air conditioning units are usually installed for a certain period of time — the hottest months of the year. When summer ends, you can easily remove the air conditioner and, once again, be able to open and close the window.

Of course, you can leave in the window unit year-round, though that’ll prevent you from opening and closing the window.

Individual AC units can also be installed into an opening cut into a room’s exterior wall. Common in motels and older apartment buildings, this sort of arrangement is more of a permanent solution: The unit stays in place, even when not in use during the winter. However, installing a “through-the-wall” air conditioner is more difficult, and more of a project for a professional to do.

What does it cost to install an air conditioner?

If you don’t want to install your window air conditioner yourself — or you’re able to go with a through-the-wall unit — you have options. If you’re purchasing a new unit, you could have it installed by the retailer. Conversely, you could hire a handyman to install it for you.

Air conditioning installation costs vary by location,but generally, the average range is between $140 and $500 for each unit being installed, according to HomeAdvisor. Here’s how the price breaks down.

Cost to Replace Window Air Conditioner
Remove Old AC	$40-$120
New Unit	$150-$1,100
Installation	$60-$200
Disposal	$25-$50
Total	$275-$1,470

Source: HomeAdvisor

Final word on installing an air conditioner

When selecting a window air conditioner, it’s important to choose the right size unit for the room or rooms you want to cool. If the unit is too small, it’ll struggle to cool the space and operate less efficiently. If the unit is too large, it will cool the space quickly but will cycle on and off, which is less efficient than running constantly.

While the thought of installing a window air conditioner yourself may be intimidating, it is definitely a do-able DIY project that two people working together can achieve — saving as much as $500 (not to mention the time waiting around for an appointment with a pro).

FAQ

- Affordable: Window AC units are generally more affordable than other types of air conditioners, so you can enjoy cool comfort without spending a lot of money.
- Targeted cooling: If you don’t want to cool an entire house, window AC units let you only cool the rooms you use most. Additionally, by precisely cooling only the rooms you want to cool, you can save on energy costs.
- Compact size: By sizing the unit to the room you want to cool, you ensure that it cools the space you want it to without wasting energy.
- Installation flexibility: You can place a window AC unit in just about any room you want to cool. An individual can install and remove it in cooler weather — no professional needed.
- Low maintenance: Window ACs don’t require much upkeep and are easy to control.
- Danger/security threat: If you install a window AC unit on the ground floor, you could create a vulnerable area — an intruder could remove it to get access to your home. On higher floors, AC units could fall and cause damage or injury. Make sure you’ve sized and/or reinforced the window properly before installing a unit.
- Inefficient: Window AC units are not efficient for cooling larger homes and, being room-specific, lead to “dead zones” in hallways, foyers and other connective spaces. While individually cheaper, window units in multiple rooms tend to be more expensive than a central air conditioning system.
- Drainage problems: Window AC units remove water from the air and drip it outside of the window. This could prove to be a problem if you don’t have a good drainage system underneath.
- Unaesthetic: Window AC units are not unobtrusive: They are visible from both inside the room and the outside of the building. Additionally, they may block views and light from the window.

Written by

Troy Segal

Senior editor, Home Lending

Key takeaways

How to install an air conditioner

What do you need for installation?

AC installation steps

Temporary vs. permanent AC installation

What does it cost to install an air conditioner?

Final word on installing an air conditioner

FAQ

How does a window air conditioner unit work?

What are the advantages of a window air conditioner unit?

What are the drawbacks of a window air conditioner unit?

What type of air conditioner works best for different home settings?

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