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How Do I Calculate What Size Air Conditioner I Need?

Edited ByW.S Amin Hours Updated onJanuary 20, 2023 Categories AC

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Are you looking to install an air conditioner in your home but don’t know what size to get?

Calculating the right size air conditioner for your home can be tricky.

In this blog post, we’ll provide an in-depth guide for determining the best size air conditioner for your home.

From calculating the square footage of the room to understanding the different types of air conditioners available, we’ll make sure you have all the information you need to make an informed decision.

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.

How Do I Calculate What Size Air Conditioner I Need

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
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.

What Size Air Conditioner For A 14×70 Mobile Home?

Measure The Square Footage Of Your Area
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.

What Size Generator To Run A 6000 BTU Air Conditioner?

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
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.
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 areaAn air conditioner with a minimum BTU requirement
100 to 150 sq ft5,000 BTUs
150 to 250 sq ft6,000 BTUs
250 to 300 sq ft7,000 BTUs
300 to 350 sq ft8,000 BTUs
350 to 400 sq ft9,000 BTUs
400 to 450 sq ft10,000 BTUs
450 to 550 sq ft12,000 BTUs
550 to 700 sq ft14,000 BTUs
700 to 1,000 sq ft18,000 BTUs
1,000 to 1,200 sq ft21,000 BTUs
1,200 to 1,400 sq ft23,000 BTUs

What Size Generator To Run Central Air Conditioner?

Kilowatt Method

Air Conditioner For Home
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.

What Size AC Unit For 1000 Square Foot House?

Air Conditioner For Shop
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 areaAir conditioner with minimum kW requirement
10m2 to 25m22.5 kW
25m2 to 35m23.5 kW
35m2 to 60m25-6 kW
60m2 to 85m27-8.5 kW
85m2 to 95m29-9.4 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 For A Double Wide Mobile Home?

What Size Air Conditioner Do You Need?

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

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

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

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.

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My name is Shanto and I am the editor in chief of the popular blog, "What Size Bro." Our mission is to help everyone find the perfect product, whether it is for home improvement or for electronic gadgets. We believe that every guy deserves to have the perfect size for whatever he is using.

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