How Do I Calculate What Size Air Conditioner I Need?
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How do I calculate what size air conditioner I need? Though it’s a common question, people hardly know the right method.
But determining the right size AC unit is vital to saving energy bills, ensuring efficient running, and keeping the area cool for a long time.
The following are the two most effective yet simple methods for calculating the appropriate size air conditioner for your home, office, or shop of any shape or size.
Read the guide thoroughly and choose any of the preferred methods to go one step ahead of enjoying the most satisfying cooling performance of your AC.
How Do I Calculate What Size Air Conditioner I Need?
There are a number of methods you can follow to measure the right size of AC for your needs.
But the simplest is to multiply the length and width of your home and then multiply the result by 20.
The total result will be the amount of BTUs required for the ac to cool your desired area.
Air Conditioner Size Calculation- Two Most Effective Methods
Square Footage Method
Understand The British Thermal Units
The British thermal unit (BTU) is the preferred unit for measuring the amount of heat needed to increase the temperature of a pound of water by one degree.
It is an odd metric in the USA, where many people avoid British measurement units. Still, the HVAC industry follows BTU’s method to calculate cooling capacity.
According to this method, one BTU represents the amount of heat an AC can remove within 1 hour.
The amount of BTUs required for an air conditioner is determined by a variety of factors.
Measure The Square Footage Of Your Area
If you need to cool a single room, calculating what size air conditioner you’ll need will be much easier.
If your area is rectangular or square, simply multiply its width and length to get the square footage measurement.
But if your desired area is triangular, you have to go through an extra step and divide the result by two.
If the shape of your room is more complex, break it into smaller squares and triangles. Then combine the measurements of these sections.
If you need an air conditioner to cool the whole home, repeat the same calculation process for each room and add up the total.
Remember, you have to only calculate the living space, excluding the area that doesn’t need to be cooled.
Lastly, if you have a rectangle or square house, multiply its length and width to get the overall square footage in one step.
Multiply your square footage by 20
Though you can follow several methods to determine the number of BTUs required per sq ft, multiplying by 20 is a good decision.
Multiply your calculated square footage by 20 and you will get a good approximate figure of the capacity AC you require.
Adjust Based On The Following Factors
Calculating the sq ft and multiplying by 20 will give you a rough estimate of the BTU requirements.
Apart from that, there are plenty of factors to consider to get the exact capacity air conditioner.
According to the Department of Energy and the U.S. Environmental Protection Agency, the recommendations are:
- For a heavily shaded home, deduct 10% of the capacity. Conversely, add an extra 10% capacity if your home is under direct sunlight, like in states like Arizona and Phoenix.
- If you have a family with more than two people, add an extra 600 BTUs.
- If you need an air conditioner, especially for the kitchen, add 4000 BTUs to the measurement.
Find The Correct Size Air Conditioner Based On The Calculations.
To get the right size air conditioner, multiply the length and width of the room or desired area to make it cool.
Then multiply the measurement by 20 or 25.
This way, you’ll get the right air conditioner that will keep the area cool throughout the year, whether it is a rainy, hot, humid, or sunny day. For example,
Let’s say, you need an air conditioner for a room that’s 15 feet wide and 20 feet long.
So the measurement will be 15 x 20 = 300 sq ft.
Then multiply the result by 20 BTU per square foot and you’ll get the air conditioner with the minimum capacity requirement.
It means you’ll need 300 x 20 = 6000 BTU of cooling capacity.
Following are some standard size air conditioners require for different areas:
| Range of square footage area | An air conditioner with a minimum BTU requirement |
|---|---|
| 100 to 150 sq ft | 5,000 BTUs |
| 150 to 250 sq ft | 6,000 BTUs |
| 250 to 300 sq ft | 7,000 BTUs |
| 300 to 350 sq ft | 8,000 BTUs |
| 350 to 400 sq ft | 9,000 BTUs |
| 400 to 450 sq ft | 10,000 BTUs |
| 450 to 550 sq ft | 12,000 BTUs |
| 550 to 700 sq ft | 14,000 BTUs |
| 700 to 1,000 sq ft | 18,000 BTUs |
| 1,000 to 1,200 sq ft | 21,000 BTUs |
| 1,200 to 1,400 sq ft | 23,000 BTUs |
Kilowatt Method
Air Conditioner For Home
Similar to the BTUs method, firstly multiply the width and the length of the room. Then multiply the result by watts that vary based on the ceiling heights. The rules are:
- If the room has 8 feet high ceiling, multiply the square footage by 150 watts.
- If the ceiling of the room is 9 feet high, multiply the floor space by 160 watts.
- If the room has 10 feet high ceiling, multiply the total result by 175 watts.
Air Conditioner For Office
It needs to follow a different method to calculate the right size AC unit for the office.
The reason is that offices are generally made of different materials and mostly don’t have insulation.
Therefore the office requires a bigger size air conditioner for cooling. In general, a 2.5kW air conditioner is suitable for a 10m2 office area.
Air Conditioner For Shop
Typically, Shops require an oversized air conditioner. Considering the type of shop, you’ll require a lot of money to install an AC unit.
Despite this, most of the shops aren’t insulated properly, thus the room doesn’t remain cool for long.
Generally, a 4Kw air conditioner is a preferable size for serving a 20 square meter shop area efficiently.
Following are some air conditioners require for various miter square areas based on the kW capacity:
| Range of square meter area | Air conditioner with minimum kW requirement |
|---|---|
| 10m2 to 25m2 | 2.5 kW |
| 25m2 to 35m2 | 3.5 kW |
| 35m2 to 60m2 | 5-6 kW |
| 60m2 to 85m2 | 7-8.5 kW |
| 85m2 to 95m2 | 9-9.4 kW |
After determining the amount of BTUs that requires cooling your desired area, your next step is to bout the air conditioner that can provide it.
When it’s come to installation, it’s better to let it handles by a professional to place it in the right spot.
As you get the minimum requirement, you may now wonder whether the AC could be smaller or bigger.
Following the section, we will briefly discuss the consequences of both conditions.
What Size Air Conditioner Do You Need?
Choosing the right size air conditioner is quite a simple process, however, the individual’s preferences make it complex.
As a shortcut and easier method, people often go with guesswork and make mistakes. The most common mistake is people go for either a smaller or larger one.
Let’s look at what they will bring:
Oversized Air Conditioner
Some people believe that purchasing a larger air conditioner that requires less energy will run less, save electricity and cool the area quickly. But they are wrong.
A bigger air conditioner runs irregularly and pushes the humidity of the home out of whack.
And this impacts negatively on electricity usage and comfort. The reason is that it will feel hot and sticky more quickly.
Though an oversized AC unit will cool the air quickly, due to irregular use, it won’t extract moisture from the air properly.
This will make you feel like you’re camping in a foggy, clammy, and cool environment at night.
Due to the irregular operation, the parts of the air conditioner can wear out quicker than normal.
It is worth remembering that capacity is the main consideration when measuring the cost of an air conditioner.
An oversized air conditioner will cost extra, unnecessary money.
Undersized Air Conditioner
In contrast, people who live in more moderate weather believe that an undersized AC will fulfill their demand.
They also consider the smaller unit more cost-friendly and energy-saving.
But the truth is that undersized AC needs to run longer, which will accomplish the opposite of your expectations.
So it’s safer to get an appropriate-sized air conditioner and set it at a lower temperature to get the best performance.
Variables That Affect The Sizing Of An Air Conditioner
The square footage of the home is one of the key factors in determining the right size of the air conditioner.
The other factors that affect the efficiency of your cooling system are:
Climate
Warm areas need to run the air conditioner more frequently than in the summer months.
In such an area, you’ll get more benefits from an air conditioner with a higher SEER rating.
Home Exterior
The type and color of the material on the exterior of the home affect heat reflection and absorption.
For example, lighter colors reflect the sun’s heat, while brick absorbs it and retains it for longer. Vinyl sliding ensures excellent insulation.
Shade And Sun Exposure
If your home is facing west or south, it will take a longer time to become cool. The reason is that heat from the sun is usually exposed in the summer.
Conversely, a home with lots of shade or facing east or north will remain cooler. The reason is that these homes aren’t exposed to the sun the most.
Insulation
The insulation system in the home has a great effect on the temperature of the home during both summer and winter.
A well-insulated house lets the air conditioner run more efficiently.
Windows
If your home has a single panel and plenty of windows, you will lose lots of energy.
Single-pane windows are significantly less energy efficient than double- and triple-pane windows. It means you’ll need a large tonnage AC unit.
Ceiling height
A home with a higher ceiling has more volume compared to a home with a 9-foot ceiling.
For such a home, you have to consider 1 or 2 BTUs more than the requirement for square footage to cool the area more efficiently.
Heat Producing Appliances
In general, the laundry room and kitchen contain appliances that produce heat.
To keep these rooms cool, you’ll need an air conditioner with more BTUs.
Pro Tips To Remember While Buying An AC Unit
If you want more efficiency and better cooling performance, install a wall-mounted built-in AC unit rather than a window unit.
The reason is that the window air conditioner usually sits lower in the room. Conversely, a wall-mounted AC unit sits around 5 to 6 feet above the floor.
An air conditioner with higher-placed cold filtering brings some extra benefits. It will stir the air in the room and cool the temperature of the room thoroughly.
The higher the AC thermostat is placed in the air conditioner, the better it will be for mounting between the units.
With a built-in design, you can easily pull the unit out for cleaning and remove it to store it during the winter.
Final Words
Purchasing or installing an air conditioner isn’t as difficult as determining the right size.
But the efficiency and quality of the AC unit largely depend on purchasing the exact size based on the requirements.
After reading this guide, I hope now you don’t need to wonder anymore how do I calculate what size air conditioner I need.
Lastly, the square footage method is preferable to KW, and it’s easy to pick the exact size based on the BTUs as well.
