If you want the best air conditioners to keep your house cool, you need to know what ratings and numbers to look for. A portable unit will often list its BTUs and tonnage. But determining watts of energy is a little trickier. Instead of listing base wattage, most units list an EER rating. Understanding how many watts does a portable air conditioner use can help you estimate your operating cost.


  • The Energy Efficiency Ratio (EER) determines the connection between watts per hour and British Thermal Units (BTUs).
  • The higher the EER rating, the better.
  • Different manufacturers and units use different watts per hour.

Size and Wattage of Air Conditioner Units

Many factors go into buying good portable AC units. And if you have one, knowing how often to service an air conditioner keeps a good unit running. If you’re still in the market, however, you’ll want a unit that can remove the right BTUs of heat per hour for your space. To get a good measure of this you will need to know how many tons of air conditioning do I need. For that, you’ll need a unit’s BTU number. Which, along with the EER can be used to determine the watts of electricity a unit will use.

Insider Tip

Knowing the BTUs to Kilowatt formula can help you find the right unit for you among all the various air conditioner sizes.


As a rule of thumb, the watts per hour of an AC unit multiplied by the EER should equal the BTU of the unit. To turn the equation around and find out the number of watts a unit uses, divide the BTU by the EER. This will give you the average watts the portable unit uses.


If you want to cool the entire house, repeat this process for each unit you may purchase. Not all types of air conditioners can cool all spaces, so make sure each unit is suited to the room it is intended for.


Compare the total watts per hour from your combined AC units to the watts per hour your household currently uses. This will give you a rough estimate of how much the new units will affect energy costs.


The more hours per day you run an AC unit, the higher your energy costs will be. Similarly, check your utility bills to find out your cents per hour rate so you can get a rough idea of how much the unit’s power consumption per hour will cost.


How much power does a central air conditioner use?

The watts per hour dedicated to a central air conditioning system depends on your local climate. Generally speaking, central AC uses roughly 3,000 to 3,500 watts each hour. Warmer climates may have a wider range of AC watts because the air is warmer but the home’s insulation may be more efficient and more easily contain cold air so they can use a fan-only mode.

Do air conditioners use a lot of electricity?

Whether you opt for central, portable, or window air conditioners, it is very likely that your cooling units will use more energy than anything else in your home. Even energy-efficient models are likely to consume much more electricity than other appliances. Looking for an Energy Star appliance may help reduce an AC unit’s power drain, however.

Does the EER rating really help me save money?

The efficiency rating will save you money. Higher air conditioner efficiency means lower power consumption which lowers the average operating cost.

Where to find watt ratings?

You can often find the air conditioner wattage in the manual that comes with a newly purchased unit. The information may also be on the manufacturer’s website or may be provided on request to aid you in making an informed decision.

STAT: In warmer climates such as California, 30% of the peak electricity demand during the summer months is created by air conditioning use. (source)

Alexa Sooter

After almost a decade of freelance, Alexa has covered a variety of topics. She now brings all of that experience to Gadget Review, giving her a range of perspectives on the products she researches.

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