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How Many Watts Does An Air Conditioner Use?

Air conditioners are some of the more significant energy consumers in any household, and people often wonder how many watts an air conditioner (AC unit) draws and how much that electricity costs.

Things are not that simple since AC units come in different sizes, types, energy classes, and similar. Also, it is not the same as how the air conditioner is used and how long it operates per day.

Published: November 17, 2022.

window ac unit 1

What are BTUs, Watts, EER, SEER, ...?

Before diving more into the power and energy required by different types of air conditioners, it is a good idea to clarify a few things.

BTU and Watts

BTU stands for British Thermal Unit and is a unit of heat (energy) - obviously, BTU is also a part of the United States customary units.

BTU is defined as the amount of heat required to raise the temperature of one pound (~0.453 kg) of water by one degree Fahrenheit.

The counterpart of the BTU in the metric system of units is a calorie which is defined by the amount of heat required to raise the temperature of one gram of water by one degree Celsius.

Relation between these two units is:

1 calorie = 4.184 J (Joules)

1 BTU = 1055.06 J (Joules)

The heat power of AC units is often given in BTUs, which is wrong since it should be given in BTUs per hour. Thus, we can write:

1 BTU/hr = 0.29307107 watts = ~0.2931 watts

1 W = 3.412141635 BTU/hr = ~3.412142 BTU/hr


EER rating stands for Energy Efficiency Ratio and is calculated by dividing maximal heat output (BTUs) by maximal electric wattage (W) when an air conditioner is running at 100% output.

Thus, EER is calculated using the following formula:

EER = [Heating/Cooling Output (BTU/hr)] / [Electric Wattage] BTU/Wh

Simply, the EER rating shows the ratio between the AC unit's cooling/heating wattage and its electric requirements (watts).

Modern AC units with heat pumps (also known as heat inverters and similar) can be rather efficient, especially when compared with classic electric space heaters.

SEER rating stands for Seasonal Energy Efficiency Ratio and shows how an AC unit is efficient when NOT running at 100%.

SEER is calculated using the following formula:

SEER = [1 * EER100% + 42 * EER75% + 45 * EER50% + 12 x EER25%] / 100

where EER100%, EER75%, EER50%, and EER25% are the energy efficiency ratios of air conditioners given at different cooling loads.

Air Conditioner Tonnage

An air conditioner tonnage is a term often used in the HVAC field, and it has nothing to do with the weight of the AC unit.

An AC ton describes how much heat an air conditioner can remove from the air in one hour and equals 12000 BTUs per hour.

If these terms are confusing, the good news is that they are not absolutely required in order to approximately calculate how much electric energy an AC unit needs. But, if You want to dive in deeply into the energy/power requirements of your AC unit(s), they are almost mandatory.

AC Units: Types, BTUs, Watts

AC units come in various forms, sizes, types, energy ratings, etc.

The most common AC units and their power requirements are:

  • Window AC: 500 - 1400 Running Watts
  • Portable AC: 2700 - 4000 Running Watts
  • Mini Split AC: 700 - 2000 Running Watts
  • Central AC: 1000 - 4000 Running Watts

As one can see, we are using the term "Running Watts," which is the wattage that an AC unit requires when working continuously. On the other hand, "Starting Watts" are surge power required by an AC unit when starting, and it is usually higher than the "Running Watts."

However, as everything in life changes, so do the Starting/Running Watts - some advanced AC models start their motors slowly, drawing relatively low currents from the grid.

In order to find out exactly how much your AC unit draws, check the documentation that came with the unit.

Window AC Unit Watts and Energy Requirements

AC units are rarely operated at 100% of their nominal power. After all, when calculating SEER, it is assumed that an average AC unit operates at 100%, only 1% of its running time.

So, when calculating your own wattage and energy requirements, don't forget to include actual AC unit use in the calculation.

The following chart lists the required energy and costs for window AC unit, depending on the AC unit's power requirement.

Note: it is assumed that the AC unit is used 8 per day and that 1 kWh of electric energy costs 0.15 $US per kWh.

Window AC Unit Wattage Monthly kWh Monthly Cost Annual kWh Annual Cost
500 120 $18.00 1440 $216.00
700 168 $25.20 2016 $302.40
1000 240 $36.00 2880 $432.00
1200 288 $43.20 3456 $518.40
1400 336 $50.40 4032 $604.80

As one can see,  AC unit energy and power requirements, and in the end, the electric bill, greatly depend on the AC power setting and its daily runtime - during the summer heat, many people set their AC units to cool "just a little bit" and "forget" them until autumn ... or until the next electric bill arrives...

Central AC Unit Watts and Energy Requirements

Similarly to window AC units, required energy and costs are calculated for central AC units as well.

Note: it is assumed that the AC unit is used 8 per day and that 1 kWh of electric energy costs 0.15 $US per kWh.

Central AC Unit Wattage Monthly kWh Monthly Cost Annual kWh Annual Cost
1000 240 $36.00 2880 $432.00
1500 360 $54.00 4320 $648.00
2000 480 $72.00 5760  $864.00
2500 600 $90.00 7200  $1080.00
3000 720 $108.00 8640 $1296.00
3500 840 $126.00 10080 $1512.00
4000 960 $144.00 11520 $1728.00

So, if you are relying on the AC unit for heating and cooling, it is highly recommended to have a modern, energy high-efficient AC unit.

Can Solar Panels Power An AC Unit

If You are looking for ways how to decrease your electric bills, solar panels are the way to go.

However, solar panels are not used directly to power an AC unit - solar panels are connected to the electric grid at your home, and any energy surplus is sent into the grid, and if/when more energy is required than the solar panels can provide, the energy is pulled from the grid.

On average, solar panels' efficiency is ~50% of the installed power due to weather conditions, season, sun position, etc.

So, if you want to collect, on average, 1000W of power, you need ~2000W of solar panels.

Note: setting solar panels at home is not a very complicated task, but personally, leave it to the professionals since solar panels must be connected to the solar controller, which must be connected to your home electric system. Also, some paperwork must be done as well.

In order to increase the efficiency of your solar panels, the sun tracking system can be used, just be aware that such a system also increases the initial costs.

For more about this topic, feel free to check our Solar Powered Air Conditioner: How Many Solar Panels To Run an AC Unit article.

central ac unit 1

Frequently Asked Questions (FAQ)

Here are some of the most common Frequently Asked Questions about AC units and their power/energy requirements:

How many watts does a standard AC unit use? How many watts does it take to run a home air conditioner?

What is a "standard" AC unit? AC units differ greatly, and they, on average, require from 400 to 4000 Watts when operating at full power.

The easiest way of finding the power requirements of your AC unit is to check the documentation of the unit or to find a manufacturer's tag with serial number and other info, which also states the maximum required wattage.

How much electricity does a 12000 BTU air conditioner use per hour?

12000 BTU/hr air conditioner may require up to 1500 Running Watts and up to 2300 Starting Watts.

However, with the introduction of more and more energy-efficient AC units, these numbers change over time.

How many watts does a 2-ton central air conditioner use?

A 2-ton central air conditioner roughly equals to 24000 BTU/hr, which is ~2500-3000 Running Watts and 4000-5000 Starting Watts.

How many watts does a 4-ton AC unit use?

A 4-ton AC unit is roughly equal to 48000 BTU/hr, which can be up to 5000 Watts, but it strongly depends on the quality and energy efficiency of the unit.

Can you power the AC unit using 2000 Watts power generator?

2000 Watts power generators are able to provide 1500-2000 Running Watts and 2000-2500 Starting Watts.

If your AC unit fits these power levels, then yes, you can power such an AC unit using 2000 Watts power generator.

For more information about this topic, feel free to check our Will a 2000-Watt Generator Run an Air Conditioner? article.

Few Final Words

An energy-efficient air conditioner can increase the quality of life and can save plenty of money. Such units are not cheap, but they last for years, and investing in the such unit is often a smart move in the long run.

Solar panels can be used to power not only AC units but also other appliances as well. But, setting and connecting solar panels to the home electric system should be left to the professionals. Also, let them do all the paperwork, which is mandatory.

After all, if the solar panels are large enough, not only that one can save some money, one can even earn some money in the long run.