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How Do I Choose The Right Size Of AC Unit For Your Home

Buying a new air conditioner is expensive, so choosing wisely is crucial. You may quickly regret your purchase if you choose the wrong size, which might lead to costly problems. 

AirOstat, Inc. researched the information that consumers should know regarding air conditioners, including how to choose or determine the correct unit size for your house, how to save money, and when to engage a professional.

How To Size Your Air Conditioner

The size of an air conditioner is determined by its cooling capability rather than its dimensions. British thermal units per hour (BTUh) or British thermal units (BTUs) are used to measure the efficiency of air conditioners. 12,000 BTUs of heat are eliminated per hour by one ton of air conditioning. In other words, each square foot of living area requires 20 BTU to be cooled by an air conditioner. 

Why Does AC Size Matter

Why Does AC Size Matter?

For several reasons, AC size is essential. A modest air conditioner won’t be able to cool your entire house adequately. In warmer months, the temperature will probably be uncomfortable generally, and depending on your home’s ductwork, certain rooms may be significantly hotter than others. To keep cooling the area, the unit will operate nonstop, wearing out the unit and raising energy costs. 

When the temperature rapidly reaches the desired level, a large unit will briefly switch on to cool the area before turning it off, causing it to deteriorate more quickly due to frequent cycling. Unit stress results from operating at a hurried tempo instead of a steady one. A unit that is too big for your house may cool the area too rapidly without removing enough humidity, leaving the air overly damp and making the environment too cold, which could lead to mold growth.

What Air Conditioner Size Do I Need?

The square footage of your home will determine the size of the air conditioner you need. The only exception is if you’re buying a window air conditioner; for details, read below.

To get your home’s square footage for the primary air conditioner, multiply the length of every room by its width, then add all the results. The entire square footage should then be multiplied by 20 to determine how many BTUhs are required to cool the area. 

Energy Star advises the following modifications to get the ideal size:

  • Reduce the room’s capacity by 10% because it is severely shaded.
  • If the space is very sunny, increase capacity by 10%.
  • If the appliance is utilized in a kitchen, increase the capacity by 4,000 BTUs.
  • Add 600 BTUs for every extra person in the room if there are typically more than two individuals using it.

Air Conditioner Sizing by Home Size

  • Home size of 700 to 1,000 square feet, 18,000 AC Size (BTUs), and 1.5 AC Size (Tons).
  • Home size of 1,000 to 1,200 square feet, 21,000 AC Size (BTUs), and 1.75 Size (Tons).
  • Home size of 1,200 to 1,400 square feet, 23,000 AC Size (BTUs), and 1.92 Size (Tons).
  • Home size of 1,400 to 1,600 square feet, 24,000 AC Size (BTUs), and 2 Size (Tons).
  • Home size of 1,600 to 1,800 square feet, 27,000 AC Size (BTUs), and 2.25 Size (Tons).
  • Home size of 1,800 to 2,000 square feet, 30,000 AC Size (BTUs), and 2.5 Size (Tons).
  • Home size of 2,000 to 2,200 square feet, 33,000 AC Size (BTUs), and 2.75 Size (Tons).

Window AC Size by Room Type

Most window air conditioners have a 12,500 to 5,000 BTU cooling capability. To figure out what size you need, multiply the window AC’s square footage by the size of the room it will be in. Remember to factor in the area of any rooms that are connected without a door because the window unit will also be cooling that space. 

To calculate the square footage of a room, multiply its length by its breadth. You can use a calculator on this. Repeat this procedure for any adjacent rooms that aren’t separated by doors. You should add up the area. Your window unit must have to accommodate the complete amount of square footage. 

For various room sizes, you’ll need the following number of BTUs:

    • Small (150 to 250 square feet): 5,000 to 6,000 BTUs
    • Medium (250 to 350 square feet): 7,000 to 8,500 BTUs
    • Large (350 to 550 square feet): 9,800 to 12,500 BTUs

How Do I Choose The Right Size Of AC Unit For Your Home

Choosing the right air conditioning (AC) unit size for your home is crucial for optimal cooling efficiency and energy consumption. 

Here are the steps to help you determine the appropriate size:

  1. Calculate the square footage: Measure the square footage of the area you want to cool. Measure the length and width of a single room and multiply it together. For multiple rooms, measure each room separately and add the square footage.
  2. Use a cooling load calculation: It is recommended to perform a detailed cooling load calculation to determine the AC unit size accurately. This calculation considers various factors mentioned earlier and provides a more precise estimate. You can hire a Residential HVAC professional or use online calculators to assist with this calculation.
  3. Refer to the British Thermal Units (BTUs): The cooling capacity of an AC unit is measured in BTUs. Generally, you’ll need around 20 BTUs of cooling power for every square foot. However, this can vary depending on the factors mentioned earlier.
  4. Consider efficiency ratings: Energy efficiency is an essential factor to consider. Look for AC units with a high Seasonal Energy Efficiency Ratio (SEER) rating. A higher SEER rating indicates better energy efficiency.
  5. Consult an HVAC professional: If you need more clarification about the calculations or have specific requirements, it’s advisable to consult an HVAC professional. They can accurately evaluate your home’s cooling needs and recommend the right AC unit size.

Remember, selecting an AC unit that is too small may need help to cool your home adequately, while an oversized unit may lead to frequent cycling, poor humidity control, and higher energy bills. 

Other Factors That Affect the Size Requirements for Air Conditioners

Size considerations for AC units go beyond square footage. The following factors may slightly change the figures:

  • Ceiling height: The average ceiling height for modern homes is 9 feet, standard for AC size calculations. If your vaulted or high ceiling is higher than 9 feet, add one or two BTUs.
  • Climate: Warmer climates see more frequent use of air conditioning systems. They operate more frequently, for longer periods of time each day, and throughout the year. In these instances, a unit having a higher SEER rating is advantageous.
  •  Heat-producing appliances: Appliances in areas like kitchens and laundry rooms frequently produce heat, making it more challenging to maintain a cool environment in those spaces. For these spaces, add one or two more BTUs as well. 
  • Home facade: The siding and color of your house affect how cool it is inherently. Darker paint hues and thick building materials like brick both absorb more sunlight.
  • Insulation: Similar to this, the lesser insulation you have, the more air will escape from your home, necessitating a greater tonnage.
  • Sun exposure: Homes with minimal shade or those facing west or south absorb more sunlight and require longer to cool, which increases stress on the air conditioner. 
  • Windows: More tonnage will be required to hold cool air in the area. The more windows your home has and the less energy-efficient they are constructed to be.

What Are BTUs?

People refer to British thermal units as BTUs. It is the energy value necessary to raise a pound of water by a single degree Fahrenheit. The British thermal unit per hour (BTUh), often known as tons, is a unit used to quantify how well an air conditioner can cool space in an hour. To discover the suitable AC unit for your room, you must compute these measurements even if you are not an expert in the science of thermal units.

What Is the SEER Rating?

Seasonal Energy Efficiency Ratio is referred to as SEER. The SEER rating is calculated by dividing the cooling output of an air conditioner over a typical cooling season by the total energy utilized. A SEER rating shows how much power and cash the appliance needs to run efficiently over a year. The SEER rating rises when the unit uses less energy to generate the proper amount of cooling and vice versa. 

The US Department of Energy mandates a SEER of at least 14 in northern areas and 15 in southern states.

Reducing Air Conditioning Costs

How to Reduce Air Conditioning Costs

Federal energy regulations in place today demand greater energy efficiency compared to the past, which lowers their operating costs. To ensure an efficient device, look for an Energy Star label that indicates an energy-efficiency ratio (EER) of 10 or greater. The lower your running costs, the higher that number. 

In addition, apply the following tips and advice to increase or maintain your unit’s effectiveness:

  • Clean filter Regularly: Unless the directions for your zone-specific device specifically state otherwise, perform this needed procedure every four months regarding central air filters. Window units also require regular cleaning. Before reinstalling the filter, vacuum any significant buildup from it, wash it in warm, soapy water, and let it completely dry.
  • Optimize insulation: Proper insulation helps maintain a consistent temperature inside your home. Insulate your walls, attic, and ductwork to minimize heat transfer. It will prevent cool air from escaping and hot air from infiltrating, reducing the workload on your air conditioner.
  • Utilize a timer if you have one: If nobody is home in your specific zone, your unit only needs to operate at full capacity if needed. While you don’t want to let, your house gets so hot that your air conditioner has to operate hard to cool it down again, determining the timing of your home such that it is a few degrees warmer while no one is there and then starts cooling again when you get back is an excellent method to cut AC costs. Make sure to close all doors and windows when adjusting the temperature.
  • Maintain your system: Your air conditioning system requires proper maintenance and lasts longer, just like all your other equipment. Please keep it clean, keep window units in a dry location during the winter, and have a qualified AC technician determine and check the unit once or twice a decade to ensure it is operating at peak efficiency.

How To Hire an AC Professional

When selecting the best HVAC professional, people should know a few factors.

  • Require insurance documentation and Contractors State License Board authorization.
  • Inquire about the technician’s ability and experience, especially with your unit type.
  • To receive an itemized estimate, first request a home evaluation.
  • Consult references or browse online user reviews.
  • Lastly, base your decision on something other than cost. You could have a good or bad experience, regardless of how pricey the HVAC contractor is in any way.


Choosing the wrong air conditioner size can result in an unpleasant home, greater energy expenses, mold growth, or a cooling system that fails to last for as long as it should. When looking for a new air conditioning unit, take your time. Accurately measure the square footage of your area and adequately calculate BTUs. Look at the Energy Star rating and SEER rating. Verify a professional’s credentials before hiring them. Making a better investment will result from spending more time doing the research.

Get Professional AC Installation

Are you seeking an HVAC contractor or a professional AC installation service for your residential home improvement space? AirOstat, Inc. is here for you. Our experienced technicians are ready to provide you with top-notch repair and installation services that ensure optimal cooling and comfort in your home. 

If you are still trying to decide on the right size for your AC unit and have questions, please call us at (844) 247-6782.