What size window air conditioner do I need? [12 things to consider when choosing Window AC unit)

It is important that you choose the right window air conditioner size as it affects the efficiency. While manufacturers’ will indicate the window size that best fits the AC unit, you also need to consider other factors listed in this article. Read through and get your answer to the What size window air conditioner do I need? question.

 12 things to consider when choosing the right window air conditioner to buy

what size window air conditioner do i need...Frigdaire FFRE0833S1 8000 BTUs

1.      What is the type and size of window will you install the air conditioner?

The window may be the standard one that sides up and down. It may also be the slider window that slide left and right. Or it could be the casement windows that simply swing out.

Measure the window size (width, height and depth) and compare against the specific air conditioner recommended specification.

The air conditioners have side panels on either side to fill out the space left between the actual AC and window frame.

2.     What is the size of the room and the What size window air conditioner do I need question

When considering what size window air conditioner you need, consider the room you plan to install. How big is it? Usually you measure the size in square feet.   Remember the    mathematical formula for calculating area of a square, rectangle, triangle etc.(length*width for rectangle,  divide by 2 if its a triangle)?

Apply the formula to calculate the area of your room.  For irregular shaped  rooms,  subdivide into squares, rectangles, triangles etc  and the  add the respective areas to get the  total room  footage.

3.     What size window air conditioner do I need and the How many BTU capacity

When reviewing the window AC units, the term BTU will feature quit often. The BTU (British Thermal Units) of an air conditioner measures the thermal energy. The BTU determines the capacity of your Air Conditioning unit.

A big air conditioner serves a larger space and consequently equipped with more BTUs and weight.

Do not choose a window AC with too little BTU power as it will run continuously trying to cool a large room  and consequently consuming a lot of power without achieving its’ objective.

Alternatively, an AC unit that is too big for the room size  will cool the room before it dehumidifies. Since  a room air conditioner is supposed to cool and dehumidify  concurrently, you might end up with a cool damp space.

4.     Your room size vs the AC unit BTUs

Now that you have the square footage of the room, use the table below as a guide to decide on the window AC unit size that answers the What size window air conditioner do I need question.

While at it adjust the BTUs taking into consideration of the other factors listed below the table to objectively determine the BTU requirement.

Room sizeBTUs Capacity Needed Per Hour
100 - 150 sq. ft.5,000 BTUs
150 - 250 sq. ft.6,000 BTUs
250 - 300 sq. ft.7,000 BTUs
300 - 350 sq. ft.8,000 BTUs
350 - 400 sq. ft.9,000 BTUs
400 - 450 sq. ft.10,000 BTUs
450 - 550 sq. ft.12,000 BTUs
550 - 700 sq. ft.14,000 BTUs
700 - 1,000 sq. ft.18,000 BTUs
1,000 - 1,200 sq. ft.21,000 BTUs
1,200 - 1,400 sq. ft.23,000 BTUs
1,400 - 1,500 sq. ft.23,000 BTUs
1,500 - 2,000 sq. ft.30,000 BTUs
2,000 - 2,500 sq. ft.34,000 BTUs
  • Is the ceiling more than the usual 8 feet? Increase the BTUs.
  • The regular BTU on the table is allowed for 2 people. For every extra person, increase the BTU capacity by 600 Units.
  • The kitchen is a place where heat is generated as a matter of course. Add 4000 BTUs to the room size capacity.
  • Does your room enjoy more sunlight, adjust the BTU capacity upwards by 10%. If nicely shaded, reduce by 10%.

5.     The environment and the What size window air conditioner do I need question

what size window air conditioner do I need-shadeYou will need to factor in the amount of sunlight and thus heat the room is exposed to.  Windows allow more sunlight into the room. So, how many windows does the room have, how big and what direction do they face?

Western facing windows receive most heat unless the room exterior has a shade. Keeping the exterior of the room you’re cooling shaded will assist the AC unit to in cooling the room and possibly require a less capacity AC unit.

However, ensure that whatever is providing the shade is not restricting airflow around the exterior of the Air conditioning unit.

6.     Your electrical power specifications

Know your specifications and ensure that your choice AC unit plug is compatible with your power outlet voltage and amperage.  Whereas most window AC units below 15000 BTUs will fit in most homes, larger units may require more voltage and amperage.

If the What size window air conditioner do I need answer happens to be a high capacity air conditioner, upgrade the electrical power capacity and thus   prevent circuit breaks.

7.      The Energy Efficiency

You want to save energy and money? Be on the look-out for energy star rating and /or energy efficiency ratio (EER).


The EER refers to the number of BTUs the unit uses for each watt of power and as such, the higher the EER, the higher the efficiency. The U.S. Department of Energy recommends an EER of at least 10.0 to save energy and costs

Energy star rating

what size window air conditioner do i need...Energy starWidow AC units that carry an ENERGY STAR have met strict energy efficiency guidelines as set by the U.S. Environmental Protection Agency and the U.S. Department of Energy.

The AC units with an energy star rating use 9% less energy (Source) than similar models that do not have the star.  You may even find that you get a rebate from your state when you purchase an Energy Star rated AC unit!

8.     Maintenance

As with any other appliance, your window air conditioner will certainly need maintenance for consistent optimal performance. Dust, dirt and other debris accumulate on or inside the AC unit and thus require cleaning.

The filter requires more regular cleaning. Ensure that you can easily access, remove, clean and reassemble the filter. The machine also needs an annual clean up and an air conditioning unit with slide-out chassis is a plus.

Some manufacturers come with inbuilt mechanism that traps pest while allowing condensation to drain out.

Review the manufacturer’s user manual on the maintenance guidelines.

9.     Window location

A centrally located Window installation is likely to give a better performance.

However, if you can only install on a window that is near the corner of a room, choose the window air conditioning unit that can direct airflow to the desired.

If the mounting can only be at the far end of a long room, chose an AC unit with a “turbo” fan mode to push air further into the room.

10. Noise levels

While windows AC units are relatively quiet on low setting, the noise level may increase on high setting. Should you be a light sleeper, the noise may be a disturbance when sleeping.  A noisy AC unit may also be a distraction in an office.

11.   Warranty

How long is the warranty?  Do you get technical support?  Choose an AC unit with a longer the warranty as it means the manufacturer has more confidence in the product.

12.  Additional efficiency and convenience features

The features listed below either improve efficiency or make the window AC unit easier to operate.

  • What is the dehumidification capability per hour?
  • Does the unit have a filter alert thatsignals the need for cleaning.
  • Can you set the unit to switch on before you get into the house and off when you are deep asleep. Get an AC unit with an inbuilt Timer and you are good to go.
  • Don’t you just love easy to use logically arranged controls irrespective of whether they are mechanical or electronic? All the same, electronic controls allow you more flexibility.
  • What about adjusting the controls from your desired comfort zone? Choose a window air conditioner has a remote control.
  • What are the venting options? Would you prefer to recirculate room air, exhaust room air outside or pull in air from outside?
  • Does the AC unit have a sleep mode setting? Then, the room temperature will increase gradually as you sleep and thus reducing pressure on the compressor and subsequently reduced noise.
  • What about cleaning the air? Well a choice of a window AC unit that comes with an electronic ionizer will assist the AC to more efficiently remove air impurities.
  • And what about the cord length size? Well, the longer, the better as it means that you do not have to add an extension cable.

Window air conditioners are a great choice and energy efficient when cooling your room. While choosing one, make sure you have clearly answered the What size window air conditioner do I need question. Follow the considerations and select a Window AC that will cool your room for a long time.

Follow this link for the smallest window air conditioners

And should your window be vertical, narrow casement or sliding, click here

For the  quietest portable air  conditioner, click here

Vicky Geem

Hi there, I'm Vicky!- an ardent reader, researcher and writer. And I love breathing in cool, clean, healthy air. No wonder the interest in information and products that cool, heat, moisturize or purify the air in our living spaces. At BestAirconHeaters.com, I share this information with you in a way that helps you make better and wiser decisions. When I’m not reading, researching or writing, you are most likely to find me enjoying the cleaner air outdoors. Or minding what I eat as I tend to my kitchen garden, picking some and ... meet you in the kitchen! Or contact me on email vickygeem@gmail.com  or facebook/vickygeem

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