How much does a window AC unit cost to run? Calculate the costs

Written by Adam Morris
8 Min read
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Table of contents

Air conditioning is one of those things you don’t really appreciate until you really need it! There’s nothing quite like the feeling of relief you get when you walk in from a scorching hot day outside to a cool and welcoming house. It makes everything so much easier - sleeping, working, and even simply walking around.

But for some, installing central air conditioning simply isn’t an option – whether that’s because of financial constraints or logistical reasons, but they still want to be able to benefit from all the positive aspects of air conditioning. If this is the case, a window AC unit might just be the next best thing.

About window air conditioning

A window air conditioning unit is perhaps the simplest and most accessible form of home air conditioning available. It’s a single unit that contains all the elements, parts, and components within a sealed casing.

Window air conditioning is extremely convenient and versatile, operating outside of your central HVAC system. It is designed to be mounted on a window but is versatile enough to be able to be moved around the house to wherever you need it. If the room has a window, the window air conditioning unit will work there.

How does window air conditioning work?

Air conditioning units don’t actually ‘make’ cold air in the same way a furnace produces heat but contain many moving parts to cool down warm air. These parts include:

  • Compressor – Responsible for moving the refrigerant between the evaporator coil and the condenser coil
  • Fan – sucks in hot air from the room before dispelling it into the outside
  • Blower – circulates hot air over the evaporator to cool it down before expelling the wonderfully cool air into the room
  • Condenser coils – cools down the hot air that the fan/blower has sucked in
  • Evaporator coils – made from copper, steel, or aluminum its main job is to cool the refrigerant so that it can absorb the heat. As the fan blows air over the coil, the refrigerant becomes cold and turns into vapor, then absorbs heat before flowing to the outside unit where it is compressed to become a hot gas
  • Chemical refrigerant – The substance used by the evaporator coil to remove heat and humidity from the air sucked in from your room
  • Filter – Removes dust particles from the hot air that is sucked in from the room
  • Thermostat – Controls the temperature and flow rate of the cold air and is usually mounted on the opposite wall from the air conditioning unit
  • Expansion valve – Situated in between the evaporator coils and condenser coils and works by ‘throttling’ to bring down the temperature of the air

Different types of air conditioning units

There are a number of different air conditioning units available and finding the right one for your home depends on your specific needs and requirements. If you’re in the process of researching air conditioning, here’s a quick rundown of the different options you’ll come across:

Central air conditioning

Central air conditioning units work by circulating cool air through ducts that are positioned inside of walls. Because of the level of work involved in channelling out walls in older properties, central air conditioning is now more commonly only found in new builds.

There are two different types of central air conditioners – split systems and packaged systems. Split systems comprise both an indoor and outdoor unit that are housed in cabinets and connected via copper pipes. Packaged systems rely on a single cabinet that is situated on a roof or within the foundations of the house.

These types of units are energy efficient, cost-effective, and work extremely well at cooling down entire homes.

Portable air conditioners

These are a convenient alternative to central air conditioning and are ideal for moving from room to room. They work by pulling hot air from the room to the inside of the unit, the motor then cools the air ready to be released back into the environment. It also takes warm air and excess moisture and sends it outside via a hose through the window.

Most portable air conditioners feature programmers which enable you to set the times you would like the machine to turn on and off.  This means you can enjoy walking into a wonderfully cool home after a long hot day outdoors, but ensure it switches off automatically during the night when you’re asleep.

One drawback to portable air conditioning units, as opposed to central air or window air conditioning, is the noise level. Portable air conditioners tend to be fairly noisy, with some of the more poorly sound-proofed models reaching 70-75dB.

Evaporative air conditioners

The technology behind evaporative air conditioning units dates back to ancient Egypt and uses air and water rather than chemical refrigerants.

They work by drawing heat and excess moisture through moisture pads which is then cooled and circulated through the home using a simple fan. Not ideal for use in very humid weather climates, these systems work best in areas where the weather is hot and dry.

How much electricity does a window AC unit use?

Of course, the answer to this isn’t a straightforward one as it depends on many factors! The make and model of the AC unit, the outside weather conditions the air conditioner will have to deal with, and most importantly the power consumption of your appliance.

A quick guide to power consumption

As a quick guide, the power consumption of a large window air conditioning unit is between 1,400 and 2,000 watts per hour, medium units will use around 900 watts, and smaller ones around 500 watts.

You can calculate the watts per hour (energy consumption rate) of your appliance by checking the handbook, which you may have as a physical copy but can most likely be found online if not. The information will probably be presented in kilowatts and it’s worth remembering that 1 kilowatt is equivalent to 1,000 watts.

How to calculate how much electricity your window AC unit will use a month

  1. Write down how many hours a day you will be using your window air conditioning unit
  2. Calculate the power consumption (watts) of your specific window air conditioning unit
  3. Calculate the monthly consumption using this formula: AC wattage X AC usage in hours per day X number of days

How to calculate how much your window AC unit electricity will cost

  1. Establish the cost of electricity in your area
  2. Calculate your monthly electricity consumption using the formula above
  3. Calculate the monthly electricity costs using this formula: cost of electricity ($kWh) X monthly power consumption

Which factors affect how much electricity your window AC unit will use

There are a number of factors that will affect how much energy your air conditioner uses, including:

  • The temperature outside
  • The size of your unit
  • The thermostat setting
  • The cooling load
  • The EER rating of the unit

The outside temperature

Most air conditioning units are designed to function with outside temperatures that don’t exceed 100 degrees, if temperatures exceed this level, they consume much more energy which leaves them susceptible to malfunctioning.

When temperatures exceed 95 degrees your air conditioning unit will be running at its maximum capacity, keeping temperatures inside the room between 78-80 degrees.

The size of your window AC unit

It goes without saying, but size really does matter! (Or at least it does when trying to keep your air conditioning costs down)

Larger air conditioning units will use more electricity to power but will most likely be more efficient at cooling the room. Use the calculations provided above to work out exactly how much your unit will cost you per hour to run.

The thermostat setting

In order to stay most comfortable and cool this summer, the US Department of Energy has suggested setting your thermostat to 78 degrees when you are home. This temperature will provide maximum cooling but without creating a sky-high electricity bill at the end of the month.

Any time you’re out of the house for two hours or more, turn your thermostat up 7-10 degrees Fahrenheit, this will help you save at least 10% on electricity costs. The higher temperature inside your house will slow the flow of heat into your home and it won’t take as long to cool back down again afterward.

The cooling load

The term ‘cooling load’ refers to the amount of heat energy that needs to be removed from a space to maintain a temperature in an acceptable range.

There are a number of informative articles showing how to calculate the cooling load of your air conditioning unit, such as this one here.

The EER rating of the unit

EER stands for energy efficiency ratio – in other words, the energy efficiency of your window air conditioning unit.

The higher the EER rating, the more energy efficient your unit is, and the more energy efficient your unit is the more you’ll be saving on your energy costs.

5 quick tips to reduce your air conditioning energy costs

  1. Turn it off when not in use – This applies to air conditioning units and any other appliance in your home! Don’t just switch it off using the remote as this will just set the compressor to ‘idle’ and you will still be using electricity. Instead, completely remove it from the power outlet.
  2. Make use of the timer function – Rather than letting the air conditioning run all night, set the timer for a couple of hours so that it switches off when you’re asleep.
  3. Close every door and window – In order for your conditioning to run at its maximum efficiency you should close every door and window to help the room cool more quickly
  4. Clean and maintain your air conditioning unit regularly – If the filters are covered in dust and debris your machine is going to have to work overtime and will cost you more in electricity. Unplug the unit, remove the front panel and give the filters a good clean using a cloth or vacuum attachment.
  5. Set the right temperature – Set the temperature to 78 degrees when you are at home and increase this by 7-10 degrees any time you’re out of the house for two hours or longer

Conclusion

Window air conditioning units provide an efficient and effective way to keep rooms cool in your house. However, whilst they use less energy than other home cooling systems, using them in multiple rooms or for long periods of time can increase your energy costs considerably.

Throughout this article, we have shown you how to calculate these costs and suggested several ways you can avoid a scary bill at the end of the summer.

Happy cooling!

FAQs

Are window AC units expensive to run?

Window AC units are undoubtedly cheaper to run than central air conditioning, especially if used in less than five rooms. However, if you want to cool an entire house it may work out cheaper in the long run to use central air conditioning.

Is it cheaper to run a fan or window AC?

Comparing fans and electricity is like comparing apples and oranges! They both do completely different things and therefore their costs are very different. However, on average fans use between 5-9 times less energy than an air conditioner but will not be nearly as effective at cooling down the room.

Is it cheaper to leave the AC on all day?

You can make significant savings on your energy bills if you switch your air conditioning thermostat up by 7-10 degrees any time you leave the house for two hours or more.  If you switch your air conditioning off it will have to work harder to remove the heat and moisture from the room and therefore will be cheaper to leave running all day.

Appliances made simple. 

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