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Guide to Window AC Power Consumption and Running Costs

Josh Mitchell

Written By

Josh Mitchell

Expert Reviewed By

Holly Curell

Last Updated On

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Window ACs aren’t known to be the most energy-efficient cooling solution, so it’s up to you to understand your unit’s energy consumption.

This will not only allow you to stay cool in the unbearable heat but also make it possible to save on energy costs wherever possible.

In this complete guide, I’ll cover all the basics of the average power consumption of window air conditioners, including how to determine the exact wattage of your window AC.

Key Takeaways

  • Depending upon the model and size, a Window AC can consume anywhere between 400 - 2250 watts and even higher. The higher the power consumption, the higher the bills.
  • Climate conditions, ambient temperature, thermostat, SEER rating, maintenance schedule all can impact how much power a Window AC consumes.
  • You can figure out the wattage of your AC through spec sheet, by using watt-meter or by using simple formulas.

How Many Watts Does A Window AC Use?

Every window AC unit is different, so the actual energy usage and power consumption comes down to your air conditioner's specific make and model.

Obviously, small appliances and lower BTU ratings equate to less running wattage.

Still, it comes down to more than the size and power consumption of your specific unit.

There are other factors to consider, like the outdoor climate, the size of the room being cooled, your specific thermostat settings, and the appliance's seasonal energy efficiency ratio.

Here’s a deeper look into each factor for determining how many watts your window AC unit uses:

AC Size (BTU Rating)

Checking out the BTU rating is the first step in determining how many watts an air conditioner uses. 

BTU, short for British Thermal Unit, is a measurement of the cooling or heating capacity of electrical appliances, like air conditioners and heat pumps.[1]

BTU

Wattages

5000

417 – 625 Watts

6000

500 – 750 Watts

8000

667 – 1000 Watts

10000

833 – 1250 Watts

12000

1000 – 1500 Watts

15000

1250 – 1875 Watts

18000

1500 – 2250 Watts

The higher the BTU, the higher the cooling capacity and energy usage. If your specific unit has a higher BTU, it will be capable of cooling a room quickly.

Unfortunately, it will also consume more energy to do so.

I’ll get into all the math later on, but for now, just know that a small 5000 BTU window AC will use fewer watts than a much larger 12000 BTU window AC.

For this reason, you must choose an air conditioner based on size and BTUs.

TL;DR: AC BTU or cooling capacity is the primary factor that determines the power consumption.

Outdoor Climate Conditions Impact Wattage Consumption

It doesn’t take a genius to know that the outdoor temperatures can have an immediate impact on your electric bill.

Even for central air conditioners, these units have to work harder with higher temperatures in the summer and lower temperatures in the winter.

The same goes for window ACs.

When it's a scorching 100 degrees outside, and I set my window AC to a comfortable 74 degrees, I definitely notice a slight spike in my electricity bill.[2]

This is no surprise, considering the unit uses more watts when there's a big discrepancy between indoor and outdoor temperatures.

TL;DR: The hotter the outdoor temperature, the more the AC needs to work. Hence it consumes more power resulting in increased bills.

Square Footage of the Covered Area

The square footage of the room you’re cooling helps to determine how many watts your AC uses.

Larger rooms need a higher cooling power than smaller rooms, and the wattage is also affected by things like poor insulation or furniture obstructions.

TL;DR: Larger rooms require larger AC which in turn consume more power.

Thermostat Settings

If you're anything like me, you like to walk into a chilly apartment after being scorched by the summer heat outside.

Still, just know that setting your thermostat to a low 68 degrees in the summer will require more energy consumption from your air conditioner.

TL;DR: The chillier the thermostat settings, the more power the AC will consume.

SEER Of Window Units

Seasonal Energy Efficiency Ratio, SEER for short, is the ratio of the cooling output of an air conditioner or heat pump over a typical cooling season, divided by the energy it uses in watt-hours.[3]

Basically, it’s a measurement of how effective your air conditioner is against seasonal factors, like extreme cold or heat.

The higher the SEER, the better; units with a higher SEER are more energy-efficient and not as expensive to run.

The standard SEER for window air conditioners is about 10, so try not to purchase a window AC rating below that.

Those with a rating of 14.5 or higher are Energy Star certified, and while they may be more expensive upfront, they use less wattage and save on power bills.

TL;DR: The higher the SEER rating, the lower will be its power consumption. This will also reflect in the form of lower bills.


How To Figure Out The Wattage Of Your Window AC

Now that you know all the factors involved in determining how many watts window units use, let’s get into the specifics of calculating energy consumption.

Wattage Calculation

Check The Specsheet

The easiest way to figure out the answer to "How many watts does a window AC use?" is to check the appliance's specifications sheet.

All window air conditioners come with these; even if you've thrown yours out, you can usually access it online.

The specs sheet will tell you everything you need to know about your window AC unit, including the power rating in watts, the amperage, and the voltage.

Important Note

Most ACs have their wattage rating in the spec sheet.

If you can’t find the wattage rating, just multiply the amperage by the voltage (Amps x Volts = Watts).

Use A Watt-Meter

It wasn't until recently that I invested in my first watt-meter, and I've found this little device to be handy when figuring out the wattage of any of my home appliances.

This instrument is designed to measure and estimate electrical power. All you have to do is plug it into the power outlet, then plug the AC into the watt-meter.

Most of these devices cost around $30, and they give readings on watts as well as volts, amps, hertz, and kilowatt hours.

TL;DR: A Watt-Meter tells you exactly the amount of power your AC is consuming in a particular instance. You can use this to find both max consumption and the average power consumption behavior.

Calculate Wattage Using Volts, Amps, BTU & EER

When in doubt, you can always turn to good old-fashioned math to determine the energy consumption of window AC units.

I don’t consider myself a math whiz, but a few simple formulas make it easy to answer the question, how many watts does a window AC use?

Amps X Volts = Watts

Multiplying amps by volts is a foolproof way to figure out the wattage of your window air conditioning unit. The equation couldn’t be easier: Amps x Volts = Watts.

Let's say the air conditioner runs on 10 amps of electrical current, and you're using the standard 120-volt outlet.

Simply multiply 10 by 120 to get your final answer of 1200 watts of electricity usage.

BTU/EER = Watts

Another option is to divide the unit’s BTU rating by the official Energy Efficiency Ratio, or EER.

For example, say you're using a small window AC that has a 5,000 BTU rating, and it has an EER rating of 10.

Just divide 5,000 by 10, and you're left with 500. So, in this case, the air conditioner consumes 500 watts of energy.

Cost Per Hour Formula

If you strictly want to know how much it will cost per hour to run your window AC, there's a formula for that, too.

First, you need to know the cost of your home's electricity, which will be listed in kilowatt-hours on your utility bill.

To find your cost per hour, multiply wattage by cost per kWh, then divide that number by 1,000. Here’s what it looks like:

(Watts x Cost per kWh) / 1,000 = Cost per Hour

According to the US Energy Information Administration, the average cost of electricity for residents in the US is $0.15 per kWh.[4]

Assuming that’s the case for you, here’s what the equation would look like if you’re using a 1,500-watt air conditioning unit:

(1,500 x $0.15) / 1,000 = $0.22

In this case, running a 1,500-watt unit at the average electricity cost will only set you back $0.22 per hour.

TL;DR: With simple formulas you can figure out the max wattage consumption of your AC. However, this can be misleading when calculating bills since ACs do not consume power in a linear fashion. Their consumption varies between seasons, days and even between hours of the day.


Running Costs Of Small Versus Large Window ACs

For most people, the entire point of knowing how much energy your AC consumes in watts is to have a better understanding of how much it will cost to run the appliance.

Let’s assume that the energy cost is the national average, $0.15 per kWh, and the combined Energy Efficiency Ratio is the standard 10 rating.

Here’s a breakdown of what you can expect to pay per hour to run your window unit:

BTU Rating

Wattage

Average Cost Per Hour

5,000

450

$0.07

6,000

700

$0.11

7,000

800

$0.12

10,000

1,000

$0.16

12,000

1,200

$0.18

15,000

1,500

$0.22

18,000

1,800

$0.27

25,000

2,500

$0.38

Keep in mind that these are just the average costs per hour.

There’s a lot to factor in, like real-world conditions and current climate, local electricity costs, the efficiency of the window unit, and whether you’re using a solar generator vs traditional electricity.


Tips For Keeping Running Costs Low

With electricity costs constantly on the rise, I’m constantly looking for ways to reduce my monthly utility bill.[5]

Tips

Here are a few things you can do to keep the running costs of your window unit more affordable:

  • Choose the right BTU based on the room size
  • Pay attention to outdoor temperatures
  • Understand that window air conditioners are only for supplemental cooling - it’s best to use this in conjunction with your central air conditioner
  • Don’t confuse the thermostat and make gradual changes to the settings
  • Keep up with AC maintenance with regular cleaning
  • Choose a specific model with a higher EER
  • Consider solar power (solar generators, solar panels, etc.)

TL;DR: From choosing the right BTU AC with higher SEER rating to something as simple as performing regular maintenance, all details can impact the wattage of your AC. 


FAQs

Can a 1,000-Watt Generator Run a Window Air Conditioner?

Yes, you can run a window air conditioner on a 1,000-watts size generator, but only small to medium-sized units ranging from 5,000 to 10,000 BTUs.

Anything over 10,000 BTUs needs a more significant power source, preferably a 2,000-watt generator.

How Much Power Does A Window AC Unit Use On Fan Mode Only?

Running window air conditioners on fan-only mode only consumes about 750 watts per hour.

Just keep in mind that fans don’t have a large cooling capacity, and fan-only mode won’t actually produce any cool air.

Why Is It Important To Understand Window AC Wattage?

Understanding window AC wattage is important for a few reasons.

When you know about wattage, you have a better understanding of energy costs, and it’s much easier to take the necessary steps to lower those costs.

References: 

  1. https://www.eia.gov/energyexplained/units-and-calculators/british-thermal-units.php
  2. https://www.npr.org/2023/07/19/1188328688/heat-wave-air-conditioner-tips
  3. https://www.eia.gov/todayinenergy/detail.php?id=40232
  4. https://www.eia.gov/electricity/monthly/epm_table_grapher.php?t=epmt_5_6_a
  5. https://www.eia.gov/energyexplained/electricity/prices-and-factors-affecting-prices.php
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Josh Mitchell

Founder

Josh Mitchell
My name is Josh and I am obsessed with home appliances. From portable AC units to heaters and air purifiers, I enjoy testing, learning and using these devices to improve the air quality inside my family home.

My Favorite Home Appliance?

Midea U Shaped Window Air Conditioner

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