If you’re considering a new central AC system, it’s essential to get the right size. Picking an oversized unit can waste electricity while an undersized unit might not cool your home properly. However, figuring out AC size is complex. There are many things that can affect your HVAC’s ability to cool your home. To find the correct central air conditioner size for your home, you’ll need to take several factors into account.

Square Footage

When calculating central AC size, most people start by considering square footage. The size of your home has a huge impact on the size of the air conditioner you need. A bigger home needs an air conditioner that can handle larger spaces. Most central AC unit sizes are measured in BTUs. BTUs, which are short for British Thermal Units, measure the amount of heat your air conditioner can transfer. Some units are also measured in tons which refer to the amount of heat removed in an hour. 1 ton is roughly equivalent to 12,000 BTU per hour. A higher BTU or tonnage means your AC unit is larger and more powerful.

The general rule of thumb many HVAC experts have used is that you need around 30 BTU for every square foot of space. Therefore, you can calculate a rough estimate of what size you need by multiplying your square footage times 25. Here are some common estimates for standard house sizes. Although most professionals will do a load calculation which is based on several factors beyond square footage. Square footage is a minimal part of determining the size of unit needed.

  • 1,000 square feet: 30,000 BTU
  • 1,500 square feet: 45,000BTU
  • 2,000 square feet: 60,000 BTU

For residential homes 60,000 BTU’s or 5 ton systems are the largest avilable, this is why in larger home you will see muliple systems.

Your Climate and Sun Exposure

Another thing you’ll need to consider is the area you live in. Regions with more intense heat often require a more powerful air conditioner to keep your home at a comfortable level. For example, a house in sunny Florida might need an extra ton of cooling compared to a home in Maine. Fortunately, Arizona’s climate is comparatively moderate. Though you won’t be able to get away with an undersized unit, you don’t have to oversize your unit to compensate. Most standard AC calculations work just fine with Arizona’s weather.

Don’t forget to take the climate around your house into account. Every area has its own specific microclimate which is affected by things like elevation, tree cover, and soil type. If your home is in a shady, breezy area, you can pick a slightly smaller HVAC system. However, if you’re in a bright, sunny area that’s noticeably hotter than the rest of your town, you might need a bigger unit.

There are many small details that affect how much the sun warms your home. Features like windows on the southern side of your home might require you to pick an AC system with extra BTU. Meanwhile, options like high shrubs along the western wall of your house might block sunlight and allow you to choose a slightly smaller AC unit.

Your Home’s Layout and Design

The cooled air inside your home can travel in a variety of interesting ways. If you have a well-designed duct system, it’s easy for air to circulate through your home and cool it down. However, if your ductwork is letting air get stuck in places like storage rooms or bathrooms, your air conditioner has to run longer to cool down the house. If your home has poor airflow, you might need a bigger AC unit.

Not only does your ductwork affect how air moves, but the shapes and sizes of your architectural elements also matter. Cooled air naturally sinks down and gets blocked by walls and other solid objects. Things like higher ceilings and more windows can require additional BTU to cool down. You might also need a more powerful air conditioner if you have an unusual layout that causes air to get trapped in tight corners or long hallways.

This is one of the main reasons that basic AC size calculators aren’t always correct. Even small details such as the height of your bedroom doors can impact what size of machine you need to get. To calculate a truly accurate size, you need an HVAC professional who knows a lot about airflow inside the home. For more uniquely shaped homes, they may need to measure individual spaces and use customized calculations to find the right AC size for your house.

Insulation Levels Inside Your Home

The insulation in your home has a large impact on your AC’s ability to function. When your home is poorly insulated, cooled air leaks outside of the house and makes it feel hotter. Meanwhile, if your home is unusually airtight, an AC might be able to cool down the entire home with little effort.

To figure out whether insulation will alter your air conditioner size or not, you’ll need to analyze your home closely. Generally, wood-frame homes are less insulated than brick or concrete homes, so they might need additional BTUs. However, certain types of insulation like foam board or spray foam can greatly increase a home’s insulation and reduce the number of BTUs you need.

In addition to considering the insulation level of your walls, you’ll also need to take into account whether your attic, ceilings, floors, and basement are insulated. The final insulation factor you need to consider is windows and doors. There are typically gaps around these features that can let a lot of air conditioning out. If your home has older windows that are less energy efficient, a larger AC might be necessary.

Whether You Have Any Heat-Generating Appliances

The final factor you need to take into your calculation is the types of appliances and technology you have. Most AC size calculations assume that you have a standard home with basic appliances. If you have anything unique, you can end up generating more heat that your AC has to work harder to overcome. For example, if you’re an avid home chef who has multiple ovens and gas burners, you might need a slightly larger AC system.

In modern times, there are also a lot of types of technology that can add excess heat to your home. If you’re running several, high-powered PCs in a single room or operating a huge indoor aquarium with many pumps, your home can get surprisingly hot even with the AC running. Since these sorts of systems and appliances increase your cooling needs, it’s worth mentioning them to your HVAC technician.

As you can see, a lot of factors go into calculating your central AC size. Since you can’t just plug your square footage into a formula and get a precise answer, it’s a good idea to get professional help. AC by J‘s technicians are happy to analyze your home and recommend a good AC size for your needs. In addition to helping with AC installations, our team also provides Scottsdale residents with a variety of other HVAC repair and maintenance services. To learn more about AC by J or schedule your appointment, give us a call today.

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