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Window Air Conditioner Sizing

Air Conditioner Sizing

Among the different options that you have for cooling down your home, you've now decided that a window air conditioner is the option that best matches your needs. Now, which size of air conditioner do you need to achieve the temperature you desire? When selecting a window aircon you'll need to take 2 things into account:
  1. Cooling Capacity of the unit
  2. Unit size

Window AC Cooling Capacity

You may have noticed that air conditioners are rated in BTUs. For example 8000 BTU window air conditioner, or 10000 BTU air conditioner.  But what does that really mean?

BTU Definition

BTU means British Thermal Units. In air conditioning, BTU means the amount of heat that a unit can remove in one hour. So the higher the BTU rating, the higher the amount of heat that can be removed. 

Why is it important to select the correct BTU rating?

  • If you choose a higher rating than the one you need, you may have to pay more than necessary for your electric bill.
  • On the other hand, if you choose a lower rating, you may not achieve your desired temperature. 

BTU Calculator 

Follow these steps to select the correct rating: 

1. Select the basic cooling capacity according to your space's area:

The first thing you need to do is to measure your space's area. 
Area = Width x Length
Once you have this you'll know the basic suggested cooling capacity. You can check it below:
2. How much sunlight goes inside your space? 
According to National Resources Canada, if your room has a lot of sunlight, or the window faces West or Southwest, you'll need to increase the suggested cooling capacity by 10%. If it remains most of the time under shades, in the dark, or faces North of Northeast, you can reduce the suggested cooling capacity by 10%. 
Lots of sunlight or facing West or Southwest:  increase BTUs by 10%
Not much sunlight/ facing North or Northeast: decrease BTUs by 10%
3. Check the space's insulation. 
If a room is not well insulated, the room will not cool down as easily, so you'll need a higher BTU rating. 
 Poor insulation: add 15% to suggested capacity
Source: National Resources Canada
4. Identify how many people use the space.
Select the size according to the number of people that use the space frequently (if there are more than 2 people who usually use the space, you need to increase the number of BTUs for every additional person.
 More than 2 people? Add 600 BTUs for each additional person
Source: National Resources Canada
5. Identify if there are sources of heat within the room. 
If you're going to use the unit in your kitchen or a room that has any extra heat, you should increase the suggested capacity.
 Kitchen or other warm rooms: Increase capacity by 4000 BTUs
Source: National Resources Canada
6. When are you going to run the air conditioner? 

If you only need to use your air conditioner during the night, you can reduce the cooling capacity. 
 Running air conditioner at night: Reduce capacity by 30%
 Source: National Resources Canada
7. Have in mind your ceiling height.
If your ceiling is very high you'll need to increase your AC capacity.
 High ceiling: Go for a higher capacity
8. Does your home have an open floor plan? 
If your home has an open floor plan or if the room's doors of your room remain open, you’ll need to increase the capacity of your unit. You should measure the whole area.  
     Open floor plan: Make sure to measure the whole area

    Window AC Sizing

    For window air conditioners, the unit doesn't need to be the same size as the window, because most units come with adjustable panels.  Below are the dimensions needed for each type of unit from TOSOT (please note that we're not distributing 6000BTU units at this moment): 

    Air Conditioner Window Sizes

    Need an Air Conditioner?

    If you've decided the size of aircon that you want to get, you can now select your favorite at

    TOSOT Air Conditioner


    Other articles you may like:

    How to Select the Correct Dehumidifier

    How does a Dehumidifier work

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    Use information at your own risk:  The information presented is intended for educational purposes only and is not intended to be a substitute for professional advice, diagnosis or treatment. Never disregard professional medical or home improvement advice. The information and suggestions should be discussed with a professional.  You are responsible for independently verifying the information if you intend to rely upon or use it in any way. You use all information at your own risk. 

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