Using your air conditioner as effectively as possible? Try these great tips and tricks to keep cool while saving energy and money.

Hot, wet, and muggy—truly the worst kind of summer weather to endure. It's even worse when you turn to your air conditioner for help, only to find that it isn't doing a damn thing. Or, maybe it is, but you're worried that you'll feel the pain when your energy bill arrives at the end of the month.

Fear not: we'll walk you through several common air conditioning mistakes that you might be making at home. Fixing these issues will result in faster cooling, greater comfort, less wasted energy, and a much more modest utility bill.

The worst mistake you can make happens before you even turn your AC on for the first time.

All AC window units are designed with a particular amount of "air space" in mind, and your unit won't be effective if your room is too big or too small for it to handle.

All AC window units have a British Thermal Unit (BTU) rating, typically in the range of 5,000 to 15,000. The rule of thumb is that every square foot of room space needs 20 BTU, with an additional 600 BTU for every person that regularly occupies it. You may need to increase this number by up to 10 percent if the room has high ceilings or receives a lot of sunlight.

We also don't recommend buying an AC unit that's too big, either. An oversize AC unit will pump out a lot of cool air, but it won't stay on long enough to dehumidify the room. The lingering humidity will make the room feel muggier and warmer than it is.

Here's a quick rundown of how air conditioners work: the AC unit pulls in warm air from the room. The warm air passes over a refrigerant that absorbs the heat from that air; the now-cooler air is blown back into the room while the absorbed heat is expelled outside, through the back of the unit.

This is why window AC units need to be mounted in a closed window or connected to a hose that runs outside; this is also why central AC units are located outside of the house. The "inside air" and the "outside air" need to be isolated from each other for the air conditioner to work. If your windows or doors are open, the heat that gets expelled is just going to get sucked right back in.

In fact, even if you don't have an AC unit, you shouldn't open the windows when the heat is at its peak. You learn more about this in our guide on how to keep your room cool without AC.

Let's say you leave for work at 8am and come home at 5pm. Your ideal home temperature is 72F. Is it more energy-efficient and bill-friendly to leave your AC unit on at 72F all day long? Should you turn it off as you leave and turn it back on when you return instead?

Most people think that the first method is better, but, actually, the second one uses less energy. The savings can be significant.

The hotter it is outside, the more that you'll save by using this second method. To learn more about why this is, check out our post on how to optimally set your thermostat.

After coming home from a long day at work, you step inside, only to be slammed by a thick wall of stale, 90F air. What do you do? You might think that the best course of action is to crank your AC all the way down to 65F so the room will cool faster, but that's not how air conditioning works.

Your AC unit pumps out the same "strength" of cool air at all times, whether your room is 70F or 90F. The temperature setting only tells the unit when to stop pumping out cool air; changing the setting from 70F to 65F won't speed up the process. It's the worst thing that you can do in this situation. This is because the AC unit will keep working even after it reaches your ideal temperature.

If, for example, your ideal temperature is 72F and you set the unit for 65F, the unit will keep going until the room hits 65F. Now, you're simply too cold and have unnecessarily wasted a lot of energy.

The lesson: set your AC unit to your ideal temperature and let it do the work. If you're tired of coming home to a hot and stuffy house, consider getting a smart or programmable thermostat.

There are a couple of different scenarios to run through here.

Remember how window units are designed with a certain amount of air space in mind? That air space assumes that all of the doors connected to the room are closed.

Your bedroom might be 150 square feet, but if you leave the door open while the unit runs, you've got a whole lot of hallway that you now need to factor into the equation. The cool air will leak out, and warm air will leak in. In effect, the unit is trying to cool the air in your room and outside the room, a volume it might not be rated to accommodate.

To maximize efficiency, keep the doors closed in any room that has a window unit running. This will limit the amount of air to deal with to what is contained in that room, helping speed up how quickly the air is cooled.

You probably have AC vents located in every room of your house. If all of your vents are open, the central unit is trying to cool every one of those rooms simultaneously.

The more air space that needs to be cooled, the longer it takes to cool it all down. This also means that your unit will need to stay on longer—wasted energy and higher bills.

By closing vents, you cut off rooms from the central unit and reduce the total amount of air that needs to be cooled. In rooms where the vents are open, the air will be cooled much faster. You should also keep the doors to these rooms closed for the same reason that we described above.

Most people use a fan when it's warm and switch to the AC when it's hot. Fans and ACs should not be seen as either-or, though. In fact, ACs work way better when working together with fans (Especially automated ceiling fans!).

Cool air accumulates wherever it gets dumped out. For window AC units, this means that the area right in front of the unit is coolest. For central units, the coolest areas are right around the vents.

To cool down the rest of your home, you'll have to wait for thermal transfer to get the job done naturally for you. Unfortunately, this can often be a painfully slow process; to move things along, you can force the cool air to circulate throughout the space by using a fan.

Imagine squeezing a drop of blue food coloring into a glass of cold water. If you just watch it sink without stirring, it could be some time before the particles dissipate, achieving equilibrium and distributing themselves throughout the water homogenously. The same principle applies here.

Circulating air also helps your sweat evaporate faster, which has a cooling effect on your skin. This means you can actually set your AC to a higher temperature while feeling just as comfortable, shaving a lot off of your energy bill on hot days.

To help you with this, be sure to check out the best ceiling fans to keep you cool.

No matter how clean your room is, particles are always floating around in the air that get sucked into the AC unit during operation. To prevent these particles from causing problems inside of the machine, all AC units are outfitted with particle filters.

A clean filter is crucial for optimal AC efficiency. Particle buildup reduces airflow, which forces the unit to work harder to pull in the same amount of air. At worst, a dirty filter can increase your energy bill by up to 15 percent and disrupt the unit's function, leaving you with maintenance issues to deal with long-term.

If your AC is on all day every day, you should change the filter at least once per month. If you use it less often, you can change the filter once every three months. Some window units have removable filters that can be rinsed clean; otherwise, you'll need to buy replacement filters as necessary.

Have you ever seen a window unit dripping all the time? If an AC unit is in frequent use, condensation on the inside can wreak havoc. However, well-designed AC units have ways of ridding themselves of condensation before it causes a problem.

Normally, condensation runs off and drips out on its own, where you won't have to worry about it. If something goes wrong and the condensation pools, you might find mold and bacteria growing inside.

Since air conditioners work by blowing cool air into the room, those little baddies can catch a ride and spread, colonizing elsewhere. This could lead to health issues like asthma, pneumonia, black mold invasion, and even Legionnaire's disease.

It's important to clean and service your AC units at the start of every cooling season. Never let anything disgusting live rent-free in your home.

Regular maintenance doesn't just extend your unit's lifespan. Maintenance keeps your machine operating at tip-top shape, which means faster and more efficient cooling throughout its lifetime, all while minimizing the amount of energy that it uses.

If you hear or see something weird, such as grinding or internal dripping, get it checked immediately. If something smells off, same deal.

It's better to be safe than sorry, and fixing the problem early is often cheaper than replacing the entire AC unit when it breaks down. If you can't afford an annual AC checkup, avoid procrastinating when something does go wrong.

Anything you can do to reduce heat output in your room, apartment, or house will go a long way toward making your AC unit more effective and efficient.

At the end of the day, AC units are not magic bullets. Even if you follow everything above perfectly, there may still be days when you feel hot with the AC running.

On average, your AC unit can bring your indoor temperature down to about 15F lower than whatever you've got going on outside. With the right setup, you might be able to bring the temperature down by 20F or 25F, but if it's 110F outside, you might still be left sweating.

Common sense goes a long way here. We live in the real world, not some fantasy version of reality.

To double up on your effort to stay cool, we've got a few more recommendations.

When talking about "best" temperatures to choose, there are two schools of thought:

The Temperature That's Best for Comfort and Productivity

The Temperature That's Best for Balancing Comfort and Cost.

Energy Star recommends going no lower than 78F. If that's too warm for you, drop it one degree at a time until the room becomes tolerable. What's most important here is the difference between your AC setting and the outside temperature. The greater the difference, the more it has to work and the more it'll cost. When you're away from home, it's best to set your AC to around 85F, cranking it down to your preferred temperature when you return. Most central AC units should not be set below 68F, or they will freeze up, which can damage or destroy the compressor.

Let's say that you've been away from home and your AC has been off for the entire time. It's only about 80F outside, but your house is sweltering at 90F. Before turning on the AC, there's something else you should do first.

Open two windows on opposite ends of your house. Mount window fans into each one. Set the first window fan to blow outwards and set the second window fan to blow inwards. This circulation sucks the hot air right out of your house and sends it outside.

If you live on multiple floors, the outward-blowing window fan should be on the top floor, while the inward-blowing window fan should be on the bottom floor.

Remember, heat is amplified by humidity. When there's extra moisture in the air, your body's sweat will just sit on the surface of your skin instead of evaporating and cooling you down. This is why "dry heat" is more tolerable than "wet heat," even when the dry heat is many degrees hotter.

If you live in a wet climate and your house isn't properly insulated, weather-sealed, and ventilated, you might be feeling more humidity than you should be. This humidity could be causing your house to feel much hotter than it is.

Air conditioners naturally pull moisture out of the air, but if your AC is set to 78F or higher and isn't running all the time, it could be neglecting this excess moisture, letting it just float around. In that case, a dehumidifier might work wonders for you.

Dehumidifiers are very similar to air conditioners, but, instead of being optimized to absorb heat, they're designed to absorb moisture. If you've got a humidity problem, using a dehumidifier in tandem with your AC could make your house feel 10F cooler.

If you need to upgrade, check out these options.

The Keystone LCD Window-Mounted Air Conditioner offers your home a lot of value for the price. For a room that's 150 square feet, you don't really want to go any lower than 5,000 BTU. If you do, the AC may not adequately cool the air and will end up running all the time.

This particular model has an easy-to-use front panel and comes with a remote control with remote temperature sensing. This means that, rather than gauging the temperature around the unit itself, it will keep running if a particular area of the room is still warm.

The Keystone is quieter than other units of its size. Of course, it still makes noise, but it's a solid option for bedrooms and offices where less noise is ideal.

With its 12,000 BTU rating, the LG LW1216ER can effectively cool rooms up to 400 square feet in size. You'll be hard-pressed to find a similarly priced unit that performs as well as this one.

It comes with all of the convenience features you'd expect: auto-cooling, multiple fan speeds, remote control (but no remote temperature sensing), and a washable filter that's easy to pull out from the front.

This powerful Frigidaire Window-Mounted AC unit produces 18,000 BTUs of cold air and can cool all but the largest of rooms within minutes. While the product description claims to work for rooms up to 1,000 square feet, you probably won't want to push it much higher than 800 square feet.

Convenience features include a remote control with remote temperature sensing, multiple fan speeds, an ionizer that cleans and removes particles from the air (Including pollen!), and two separate vents that allow you to direct airflow in two directions.

This model requires a 230V outlet and is not compatible with regular 115V outlets. This is typical for window AC units in the 18,000 BTU range; buyer beware, but a great choice if your home can accommodate.

Just like with everything else that you own, your AC unit is a companion with needs. Start by choosing the best one for your home and give it everything it needs in order to give you everything you need. Optimal placement, energy-efficient habits, regular maintenance, and a watchful eye will all help ensure that it can perform for years to come.

If your AC isn't getting the job done, there's usually something that you can do about it. Being proactive is better than sitting around and waiting for winter if you ask us.

Joel Lee was formerly the Editor in Chief of MakeUseOf from 2018 to 2021. He has a B.S. in Computer Science and over nine years of professional writing and editing experience.

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