When it’s hot out, keeping your house or apartment cool can be a snap with the right air conditioner. We test dozens each year for cooling performance all to make it easier for you when it’s time to buy a new unit. Window air conditioners are one of the most popular cooling systems in America. More than 6 million are sold each year. Their price is a big reason, running anywhere from $150 to $550. They also deliver.

Installation is relatively simple but you’ll need to secure the unit to the window and in some cases plug any gaps with foam and some large units can weigh up to 85 pounds so it may be too much for one person to handle. Remember, if you’ve got casement or odd sized windows, these units might not fit. Plus, some can be very noisy. Fortunately, we test for noise so you can find one that’s cool and quiet.

Here’s how to pick the right type for your space. Window units are sized according to their cooling capacities, measured in British thermal units, or BTUs, and they typically range in cooling power from 5,000 to 12,500 BTUs. But you can find higher BTUs. Generally, 5,000 to 6,000 BTUs will cool a 100 to 300 square foot room. 7,000 to 8,500 BTUs can cool a 250 to 400 square foot space and 9,800 to 12,500 BTUs should cover anything from 350 to about 650 square feet.

But you need to factor in more than just room size to get the perfect temperature. Think about these questions: how many windows are in the room? Is the ceiling high? Is the a/c in a window that gets direct sunlight? Is the room on the top floor of the house or building? Are there a lot of open doorways? Any or all of these may mean you need a more powerful unit.

Even where you live should factor into your decision. The association of home appliance manufacturers has a worksheet on its website that will help you make the right decision. Just go to cooloff.org. Look for models with programmable settings and timers so you can come home to a cool house. You can find Wi-Fi enable units that do the same things. Programmable units are just as good. Digital displays are more accurate than dials. A remote control is also convenient say when you’re in bed and you want to change the temperature or turn off the a/c.

Check the directional vents, too. Your best bet is to find an a/c with vents that can direct the air up, down, left, and right so you have as much control as possible. We also test those vents to see which really directly are the best, important if the a/c will be in the corner of a room.

You can keep cool for less by properly maintaining your window air conditioner. Here are some simple tips. At the start of each cooling season, clean or replace dirty filters, then clean the filter at least once a month and season. Some models even have filter monitors that will alert you when your filter needs to be cleaned. Vacuum the coils and fans. Seal any air leaks around the unit to keep it as energy efficient as possible.

Next step: portable air conditioners. Portable air conditioners are an option if you’ve got one window and you don’t want it blocked or your building doesn’t allow window units or you don’t want to deal with the hassle of installing a window unit every summer. You’ll pay anywhere from $250 to more than $500. They work by drawing in warm air from the room, cooling it, and then directing it back into the room. Single hose models will take some of that room air and use it to cool the unit and then exhaust that air outside through the hose.

You usually don’t need any tools to set one up, making them easier to install than window units, but we recommend you only consider this type if you have no other options. Our tests have found they only deliver about half the cooling capacity they claim and they use more energy than similarly sized window units.

A minimally better choice if a portable is your only option: a dual hose portable air conditioner. These use one hose to take the air from outside the window, pass it over the coils to help cool the unit, then another hose to exhaust that warm air back outside. In general, tests have found they do a slightly better job than single hose portables but still nothing close to the performance of window units.

Besides cooling performance, portables have other drawbacks. Most have built-in water reservoirs that may have to be drained when used in places with high humidity. However, some exhaust the water vapor back out through the hose. That’s a plus. Another issue with these models is how they connect to the window. All come with these adjustable width panels and a hose connection, some fall apart easily.

And portable might not be the best word to describe these air conditioners. Rolling around a 75-pound machine on a carpet isn’t exactly a piece of cake. And they can be even noisier than window units since all of the mechanical parts are in the room with you. You’ll want to look for portables with a remote control so you can easily adjust the temperature from your bed or a chair. All of the portables tested had digital controls and displays which are more accurate than dials.

Central air is convenient, simple to use, and unlike portable and window units, almost invisible, plus you avoid taking up window or room space. Today’s systems are much more efficient so you may want to consider updating or replacing your central air if it’s more than 10 years old to save money on your energy bills.

Installing central air can be fairly simple if you already have the ductwork, but if you don’t have the ductwork, this is a big project and some ductwork created for heating systems may not be able to handle the air volume needed for a cooling system. Something else to think about: in order to install ductwork, you’ll need to take the space from somewhere else, say a closet, and that could be an issue if your home is short on storage or on the small side.

No matter what your situation, a central a/c needs to be installed by a professional. Expect to pay anywhere from $5,000 to $15,000 depending on where you live and whether you need ductwork. Not all central air systems are created equal. Our reliability ratings can tell you which brands to pick and which to avoid.

And even though you can’t see your central air system, don’t forget about it. Hire a pro once a year to clean and flush the coils, drain pan and drainage system, vacuum the blower compartments, and check all the refrigerant compartments and mechanical parts. Seal and insulate the ductwork, keep debris and plants at least two to three feet away from the outdoor unit, and clean the indoor grills and filters monthly.

A split ductless system, sometimes called a mini split system, is similar to central air except it doesn’t, as the name implies, require ductwork. Instead, indoor wall units connect to an outside condenser. Each unit cools the room it’s in so you can have as few as one unit or several throughout your home. This is a great option if you live in an older home without the proper ductwork or one without any at all and you want to avoid tearing up the walls. You also might want to consider split ductless if you have a smaller home and you don’t want to lose any space to the ductwork.

They’re quieter than window units and more energy efficient than central a/c, plus many of the units sold today also have a heat pump you can use when it gets chilly. But split ductless systems are more expensive than window air conditioners and they require professional installation. Expect to pay anywhere from $2,000 to $10,000 for the units and installation. You’ll also still have a large unit that, while not mounted in your window, will be mounted on your wall. And the more units you need, the more you’ll spend. So if you want to cool more than a few rooms, central a/c may end up being a less expensive option.

You maintain a split ductless unit much the same way you would a window a/c. Check the air filter on the indoor unit every month when it’s in use, and outdoors, keep the unit free of debris, and make sure it’s clean. Call a pro annually to check the refrigerant level and to make sure it’s draining properly and that all mechanical parts and electrical connections are in working order. And of course, follow the instructions in your owner’s manual.