The Cost of Running a Window AC

A lot of us are feeling the pinch of inflation at the moment. A big part of those higher costs are high electricity rates. Air conditioning may be one expense that you’re considering cutting down on. But how much does it cost to run a Window AC? 

How much electricity does a Window AC use?

A window AC uses 900 – 1,400 watts of electricity an hour. That’s .9 – 1.4 kWh (kilowatt hours). That’s for a fairly standard window AC that offers 7,000 – 13,000 BTUs of cooling capacity, enough for a single room or a one-bedroom apartment at the upper end of the spectrum.

Small and Large Window AC Units

What about non-typical window ACs? Smaller units will produce just 5,000 BTUs of cooling power, only enough for a small room – a bedroom perhaps. A 5,000 BTU Window AC will use 600 – 700 watts to keep a small room cool.

Larger Window ACs can produce 24,000 BTUs of cooling power. That’s enough juice to cool a space of 1,400 – 1,500 square feet or the size of a typical three-bedroom apartment in the US. 

A 24,000 BTU Window AC will burn through 2,500 – 2,800 watts of power. That’s a lot higher than smaller models because larger air conditioning units tend to be less efficient than smaller alternatives.

A BTU (British Thermal Unit) is a measurement of thermal energy. It’s the amount of energy needed to change the temperature of one kilogram of water by a single degree Fahrenheit.

BTUs to Watts Conversion and Efficiency

There’s actually a direct conversion rate between BTUs and watts since both are units of energy.  A single watt (W) is equivalent to 3.41 BTUs of thermal energy per hour. So to convert from watts to BTUs, you would multiply your wattage by 3.41.

But we can’t use this conversion when talking about air conditioning because air conditioners are not perfectly efficient. Some energy is lost in the process of cooling your home. Different air conditioners actually produce BTUs from watts at different rates because some units are more efficient than others.

For example, let’s say we need 24,000 BTUs of cooling power. We could convert from 24,000 BTUs to 7,032 watts. But a Window AC only uses 2,500 – 2,800 watts to produce 24,000 BTUs of cooling. How is this possible?

Because air conditioners consume electrical energy and produce thermal energy. An air conditioner isn’t just using electrical energy to produce cold. Instead, it uses electrical energy to move thermal energy from inside your home to outside your home.

So the thermal energy isn’t destroyed, which wouldn’t be possible. It’s moved. This principle allows air conditioners to produce more BTUs than the strict conversion from watts to BTUs.

Air conditioners have what’s called a coefficient of performance (COP) that measures their energy efficiency. The COP is just a ratio of the watts of thermal cooling an air conditioner offers to the amount of electrical energy in watts it consumes.

Most air conditioners have a coefficient of performance of between 2  – 5. A higher COP signifies greater efficiency. 

Let’s return to our example. We know that 24,000 BTUs of cooling power require 7,032 watts of thermal energy. A given window AC uses 2,500 watts of electrical energy to move 7,032 watts of thermal energy out of your apartment an hour. 

That means your window AC has a COP of 7,032/2,500 = 2.81. That’s not very efficient but unsurprising given the lower efficiency of most larger window ACs.

How Much does it cost to run a Window AC for one hour?

The cost of running a Window AC for one hour is $0.12 – $0.32 depending on energy rates. That translates to a cost of $2.88 – $7.73 to run for 24 hours and $21.60 – $57.60 to run for 6 hours a day for a month.

We know that a typical Window AC uses 900 – 1,400 watts of energy an hour or .9 – 1.4 kWh. We can then quickly find out how much we will end up paying to run a Window AC for an hour.

Current Energy Rates and Their Effects

Energy rates are a bit weird at the moment with inflation and the war in Ukraine affecting energy costs (you might be reading this much later but that’s important context). The average cost of electricity at the moment is 23 cents per kilowatt hour or $0.23.  

Before that, rates of $0.13 per kilowatt hour were fairly typical. We’ll use those as the two ends of our energy price range. If you’re blessed by lower energy costs than we’re currently experiencing, then focus more on the lower end of our price estimate as it’s likely to be the most relevant. 

The lower end of Window AC operating costs are therefore $0.12 – $0.18 per hour. That translates to $2.88 – $4.32 to run for 24 hours and $21.60 – $32.40 to run for 6 hours a day for a month. You’d be lucky to pay that much right now.

At current US energy costs, the rate for running a Window AC for an hour is $0.20 – $0.32. That’s $4.80 – $7.73 for 24 hours and $36.00 – $57.60 to run for 6 hours a day for a month. 

Factors Influencing Window AC Operating Costs

There are other factors beyond energy costs that influence how much you should expect to pay for Window AC. You may have a more efficient AC unit than someone else and end up paying less for to cool a similar space.

Another big factor is just how powerful your Window AC is. We looked at typical Window ACs for our estimate but you might have a much more powerful unit that offers 24,000 BTUs can consume a whopping 2,500 watts of electricity an hour.

A 24,000 BTU unit consuming 2,500 watts an hour would cost $0.32 – $0.57 to run for an hour, much higher than typical units. 

Frequently Asked Questions (FAQs)

What factors affect the cost of running a window AC unit?

The cost of running a window air conditioner is influenced by several factors, including the unit’s power consumption in watts, the cost of electricity in your area, the efficiency of the AC unit, and how often you use it. Power consumption varies with the size of the unit (measured in BTUs), with larger units consuming more energy. The efficiency can be understood through the unit’s Energy Efficiency Ratio (EER) or its newer metric, the Seasonal Energy Efficiency Ratio (SEER), which indicates the amount of cooling a unit provides per watt of electricity. The cost of electricity can fluctuate due to market prices, regional differences, and seasonal demand. Additionally, how you use the AC—such as the temperature you set it at, the duration of use, and maintenance—can also impact the overall cost.

How can I calculate the exact cost of running my window AC?

To calculate the exact cost of running your window AC, you’ll need to know the unit’s wattage, the hours you plan to run it, and the cost per kilowatt-hour (kWh) of electricity in your area. First, find out the wattage of your AC unit, which is usually listed in the owner’s manual or on a label on the unit. Next, estimate the number of hours you will use the AC daily and multiply this by the wattage to get the daily watt-hours consumed. Convert this to kilowatt-hours by dividing by 1,000. Finally, multiply the kWh by your local electricity rate to find out the cost per day. Multiply this by the number of days in the month for your monthly cost.

Is it more cost-effective to run a window AC all day or only when it’s hot?

It is generally more cost-effective to run a window AC only when it’s hot and when the space is occupied. Running an AC all day can lead to unnecessary energy consumption and higher costs. Instead, using a programmable thermostat or timer to turn your AC on before you return home can help maintain comfort while saving on energy bills. Additionally, using fans to circulate the cool air, keeping blinds closed during the hottest parts of the day, and sealing any air leaks can make your AC use more efficient.

What maintenance can I do to ensure my window AC runs efficiently?

Regular maintenance is crucial for keeping your window AC running efficiently. This includes cleaning or replacing the air filter monthly during peak usage, checking the seal between the AC and the window to ensure it’s tight and leak-free, cleaning the evaporator and condenser coils, straightening any bent cooling fins, and clearing the drain channels. An AC unit free of dust and obstructions will operate more efficiently, use less energy, and cost less to run.

Can upgrading to a more efficient window AC save money in the long run?

Yes, upgrading to a more efficient window AC can save money over time. While the upfront cost of a more efficient unit may be higher, the operating costs will be lower. Look for units with a higher EER or SEER rating, which indicates better energy efficiency. Over time, the savings on your electricity bills can offset the initial investment. Additionally, some utility companies offer rebates for purchasing energy-efficient appliances, which can further reduce the overall cost.

How does the size of the room affect the cost of running a window AC?

The size of the room is a critical factor in determining the cost of running a window AC because it dictates the cooling capacity needed. A unit that’s too small for a large room will run continuously, trying to cool the space and use more energy, leading to higher costs. Conversely, an oversized unit will cool the room quickly but may result in short-cycling, where the AC turns on and off frequently, which is also inefficient. It’s important to choose a window AC with a BTU rating appropriate for the size of the room to ensure efficient operation and cost-effectiveness.

Are there any alternatives to window ACs that might be more cost-effective?

Alternatives to window ACs include central air conditioning, portable air conditioners, and evaporative coolers (also known as swamp coolers). Central air conditioning can be more efficient for cooling multiple rooms or an entire home, but the installation and maintenance costs are significantly higher. Portable air conditioners offer flexibility and can be moved from room to room, but they may be less efficient than window units. Evaporative coolers are more cost-effective in dry climates and use less energy but are not as effective in humid conditions. Each alternative has its own set of trade-offs, and the most cost-effective option will depend on your specific needs, climate, and home.