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How Big Should My Air Conditioner Be?

 |  Air Conditioning, Blog

Sizing an air conditioner properly for your home requires more than room size calculations. The amount of room sunlight (or shade), number of people in the room, and the condition of your ductwork can impact the air conditioning requirements for your home.

As a general rule of thumb, bigger is not always better when it comes to air conditioners. A higher capacity unit will not cool your house any more efficiently. House size and the contractor are the two most important factors in choosing the right air conditioning. To figure out your ideal size, try a little bit of mathematical analysis for your home using Energy Star’s square footage chart for air conditioning.

Why Air Conditioner Size Is So Important

Trane Air Conditioner sitting outside of house on ground in Gilbert AZAn oversized air conditioner will cool things down quickly, but heat and humidity from the walls will quickly warm things up again. The unit will turn on and off repeatedly to compensate. Regardless of energy efficiency ratings, your electric bill will skyrocket if you have an oversized unit installed.

An A/C system that’s too small for your house will run continuously. Depending on how small it is in relation to your house, it might never catch up to the optimal temperature. There’s just not enough power to provide rapid cooling. Nonetheless, the unit wastes far too much energy in the process.

Determining Air Conditioner Size

All units carry a rating of BTUs per hour and a measure of cooling called a “ton”. The British Thermal Unit is the amount of energy you need to heat/cool a pound of water by 1°F. One ton of cooling is equal to about 12,000 BTUs. Home air conditioners range from one to five tons.

Beyond Size and Floor Space

Floor space in your home is only one aspect to consider in your choice of the right-sized air conditioner. Here are a few others to include in the calculation.

  • Sunlit Rooms – Capacity should be increased by 10% for better cooling
  • Shaded Rooms – Reduce capacity by 10%
  • More than 2+ Occupants – Increase capacity by 600 BTUs per extra person
  • A/C Is in the Kitchen – Raise capacity by 4,000 BTUs

Window Units: If the air conditioner is level, then its drainage system works properly and the unit can run at top efficiency. You also won’t need as large a capacity of a unit if lamps, TVs, or appliances that generate heat are not in the room you are cooling. Registered by the thermostat, the heat will decrease the unit’s efficiency and trigger longer run times. Also make sure air flows directly toward the center of the room and not into corners.

Central A/C: A central air conditioning system is more complicated. Room-by-room or whole house calculations are performed by professional HVAC contractors using a standardized procedure called manual-J. Size or capacity of the system also depends on the condition of your ductwork – sealed ducts that don’t leak allow the system to run efficiently.

Right Size vs. Habits

Expert advice from an Arizona air conditioning service such as Isley’s will also help you choose the right size system. How you use the air conditioning directly impacts efficiency and the optimal size. Setting the thermostat a couple of degrees higher can substantially save on energy bills. You should definitely set the temperature higher if you won’t be home for an extended period of time.

Room size doesn’t always tell the whole story when purchasing a new A/C system. Properly sizing an air conditioner for your home is a multi-faceted process, with installation considerations and proper usage as important aspects of the sizing equation.

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