What Size AC Unit Do I Need for My Home?

outside view of home

On a muggy summer day in Atlanta, an air-conditioned room can feel like paradise. That’s why keeping your home cool with an appropriately sized AC makes all the difference. If you’re asking, “what size central AC do I need?” choosing the right size can reduce your energy costs, lengthen the system’s lifespan, and be more peaceful for the household.

Why AC Size Makes a Difference

It might seem obvious that an AC that is too small would not be effective. It would run constantly while struggling to cool the space. But a system that is too large would be equally inefficient. Cooling the space quickly, a large air conditioner would kick on and off with small changes in temperature. This draws excessive energy to start up and puts a lot of stress on the starter switch.

What to Look for in a New AC Unit

Choosing a new air conditioner takes a bit of calculation. As you assess what size AC your home needs, consider these elements.

  • Choose the style of AC system that works for your home. Installing a ducted AC makes more sense if your home is already fitted with sufficient ductwork than if you have to repair, replace, or install new ducts. If your home doesn’t have ducts, opting for ductless options gives you the ability to create separate climate spaces in your home.
  • Calculate the space you need to cool. In order to determine the size of AC your home will need, multiply the length of the room by the width to find the square footage. Combine open-space rooms that connect without a door since the cool air will spread to them as well.
  • Assess how many BTU/h of cooling your space needs. BTU/h (British Thermal Units per hour) is the AC’s cooling capacity. It shows the number of units of heat the system can expel within an hour. For a space that is 350 to 550 square feet, choosing a system that can remove 9,800 to 12,500 BTUs within an hour will keep the space comfortably cool.
  • Convert BTU/h to tons. The size of an AC unit is often noted in tons. Since a 1-ton AC can remove 12,000 BTU/h, when you know how many BTUs of cooling your space needs, you can figure out what size system to choose. Starting at 1 ton, the sizes increase by half a ton, ending at 5 tons as the largest size.
  • Choose your AC efficiency. To find the AC’s efficiency, look at its SEER (Seasonal Energy Efficiency Ratio) rating. This number indicates how many watts of power are used for the number of BTUs removed. The higher the SEER rating, the lower the amount of energy used to cool the space. To get the most efficient and affordable deal, choose a SEER rating between 15 and 18.

Related Content: How to Clean Your AC Coils

Sizing Your Home Air Conditioner

Once you find your space size and the number of BTUs of cooling needed, you have the basic elements you need to find the right size air conditioner. But there are several other factors that affect the natural heat of your home. These are a few questions to ask yourself before settling on an air conditioner.

  • Is the cooled air forced through ducts? When cooled air travels a distance through air ducts, it will warm as the warm air leaks in around it. The further the distance through the ducts, the more the air will change. Because of this, a ducted system would need a larger cooling capacity to adjust for the difference.
  • Does your home have thin insulation? Another factor to evaluate when choosing your AC is how much heat will leak in through the walls. If your home has poor insulation, your AC will have to overwork to keep your home cool.
  • Is your home in a sunny or shady spot? Regular sun exposure naturally adds heat to the home. To adjust for the amount of heat the sun can add, calculate a cooling capacity 10 percent higher for a home that receives plenty of sun. On the other hand, decrease the cooling capacity by 10 percent for a regularly shaded home.
  • How many people are commonly in your home? Body heat also plays a factor in how well an AC system can cool your home. If there are commonly more than 2 people in a room, add 600 BTUs per additional person to the amount of heat that needs to be removed.
  • What is the average temperature you can expect from the climate? While insulation should limit how much of the outdoor temperature leaks inside, the hot and humid temps of Atlanta summers can make the air conditioner work harder to keep the set temperature.
  • Will you use heat-producing appliances in your home? Cooking appliances—as well as other high-powered devices—produce a significant amount of heat as well. To account for spaces like the kitchen that are likely to add plenty of heat, increase the BTUs to remove by 4,000.

What Size AC Is Best for My House?

Now that you know your home’s footage, can understand an air conditioner’s cooling capacity and efficiency, and know several of the factors that require more or less capacity, you can better choose an AC system that fits your needs. Whether you’re considering what size central air AC to install in your home, as a general rule, estimate 20 BTUs of cooling for every square foot.

As you already learned, there are several factors that influence what size central AC your home needs. For that reason, it’s best to consult professionals before settling on a system.

Choosing Your Breaker Size

What size breaker is best for your AC unit? Pairing the right size breaker with your AC will help you optimize your energy usage and minimize breaker trips. When you have selected your AC unit, locate the minimum ampacity and maximum breaker size. You can find this information in the manual or on the system’s nameplate.

  • The minimum ampacity indicates the highest amount of energy the system should need. The technician will also use this information to choose the right gauge wire to install your air conditioner. But for safety and to follow the National Electric Code (NEC) rule of choosing a breaker that covers 20 percent more than the max load, you will want to multiply this number by 120 percent to find a sufficient breaker size.
  • The maximum breaker size indicates the largest size breaker that can support the unit without mishap. It is less energy efficient to run your AC on a larger breaker, but if it is within the maximum breaker size, it’s still possible.

Trust Atlanta’s Assured Comfort Experts with Your AC Needs

Keeping your Georgia home cool and cozy with the right size AC unit takes some calculations. After evaluating all the factors and making your estimate, consider running it by certified air conditioning experts before purchasing a new system.

Our team of professionals at Assured Comfort Heating, Air, and Plumbing® can help you calculate your air conditioner size, as well as, offer installation. For expert service, call (770) 464-5745 or request service online.