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AC installation - What Size AC To Choose?

AC installation - What Size AC To Choose?
What Size AC To Choose?

Whether you want to replace an AC in your current home, you are moving to a new home or building a new house – choosing what size air conditioning system to install is one of the important decisions you have to make since it is not a small investment. AC size does not refer to the AC unit’s dimensions, but rather to its cooling and heating capacity and is measured either in British Thermal Units (BTUs) or in tons. Improper size of an AC can create issues like inadequate cooling, high electricity bills, excessive moisture and increased wear and tear of the AC system.

AC size is too small

For example, if AC size is too small – it will take forever to cool or heat the house, desired temperature will be reached only at night making it uncomfortable during the day, since AC will be running a long time – homeowners will face high energy bills.

AC size is too large

If AC size is too large – it will reach desired temperature too quickly, therefore will be turning on and off frequently. Constantly repeating the On and OFF cycle many times throughout the day will lead to premature wear and tear of an AC unit. Since AC unit that is too large will be cooling or heating the space too quickly - it will not have time to remove moisture from the air, which may lead to mold in the house.

How to Calculate the Size of an AC system?


In general, it is considered that 1 ton of AC removes 12,000 BTUs of hot or cold air per hour. From area perspective, cooling or heating capacity of an AC unit is 20 BTU per square foot. To calculate how many BTUs you need – just simply multiply total square footage of the house by 20. You can also multiply square footage of each room by 20 and then add all numbers to obtain total BTU figure. For instance, if an area of the living space in the house is 2,000 ft it means you would need an AC unit with around 40,000 BTUs of basic capacity.


To calculate basic heating or cooling capacity of an AC system in tons simply multiply total square footage of the house by 20 and then divide by 12,000. For our example of 2,000 ft it is going to be an AC system of around 3.3 tons of basic cooling capacity.


If you thought it is going to be so easy – you are wrong 😊. Following adjustments should be made based on below criteria:

- Climate: If you live in hotter climate increase the 20 coefficient by 5-10%. So if you live in Austin area in Texas you should do so (Yeehaw!).

- Insulation: If your house is well insulated then coefficient could be reduced by 5-10%.

- Orientation: If most of the leaving space is in shadow (east or north-faced rooms) then deduct 5-10%, if most of the rooms are in sunny part of the house (west or south-faced rooms) – then 5-10% should be added to the coefficient.

- Type of rooms: If you have large kitchen or laundry room at the house – then you should probably increase the coefficient by 5-10%.

- Windows and Ceiling: If you have many windows at home or windows are large or ceiling is high you should probably add another 5-10% to the coefficient.

Total Capacity

To calculate the total capacity, you should add the adjustments to the basic capacity above. In our example you will probably get around 42,000-48,000 BTUs or 3.5-4 tons of an AC system for 2,000 sq ft.

Although it is crucial to understand how to choose the right size of AC unit for your home, an HVAC professional will perform all the calculations necessary for maximum efficiency. He will break down all the options and explain how some of the existing variables like insulation, sun exposure, large windows and high ceilings impact the total capacity calculation.

If you live in Austin area in Texas and need AC, Heat Pump, Furnace, Ductless Mini Split installation or replacement services – call us on (737) 757-7313 or send us an email at, or you can also book an appointment online or leave a request to call you back on our website. We will do our best to help you to find a solution that will meet your needs.