Choose the right size air conditioner to cool your home. Buying the right size of air conditioner is in your best interest; only the right size of unit or system will efficiently and effectively keep you and your family comfortable. Air conditioners that are too big use more electricity and leave the air in your house with excess humidity. Air conditioners that are too small do not cool your home to a comfortable temperature. Choosing the right size air conditioner requires some basic math and just a few minutes of your time. Measure the square footage of the room that you'll air condition. Use a tape measure to measure the length and width of the room. Write these measurements on your paper. If the room is not square or rectangular, divide the room into sections composed of squares and triangles and take those measurements. Calculate the square footage of the room. For a square or rectangular room, multiply the length by the width. If your room is some other shape, find the square footage of the triangular sections by multiplying 0.5 x length x width and sum each of the square and triangular sections to determine the total square footage of the room.

Determine the square footage of each room of your home if you are purchasing a central air conditioning system. Reviewing your property tax statement or contacting your county auditor's office is another way to find out the total square footage of your home. Don't include areas, like the basement, that won't be cooled. Determine the cooling capacity needed for the room or your home. Cooling capacity for room air conditioners and central air conditioning systems is measured in British Thermal Units (BTUs) per hour. my ac unit is not cooling properlyThe United States Department of Energy Energy Star website offers these guidelines for BTUs per square footage: 100 up to 300 sq. feet: 5,000 to 7,000 BTU 300 up to 550 sq. feet: 8,000 to 12,000 BTU 550 up to 1,000 sq. feet: 14,000 to 18,000 BTU 1,000 up to 1,200 sq. feet: 21,000 to 24,000 BTU 1,500 up to 2,000 sq. feetac window unit weight

: 30,000 BTU 2,000 up to 2,500 sq. feet: 34,000 BTU Things You Will Need Steel measuring tape Paper Pencil Tip References Energy Star: Properly Sized Room Air Conditioners Photo Credits Jupiterimages/Comstock/Getty Images Suggest a CorrectionChoosing the type and kind of central air conditioning system to install in your home's heating ventilation and air conditioning (HVAC) system is complicated. There are many physical factors about your home's cooling at play that directly affect the performance quality, efficiency, and the cost of how well a central air conditioning system will work in your home. how much electricity does a central air conditioning unit useYou also must consider the wide variety of central air conditioning systems, as well as their size, efficiency, and installation requirements. So, it's no wonder that homeowners can get anxious when they want to know what size air conditioner they need for their home.

Central air conditioning uses a compressor and condenser coil housed in an outside unit and an expansion valve and evaporator (also called an "A coil") mounted above the furnace heater inside your home's HVAC system. Air conditioning works by cycling refrigerant from gas to liquid and then to gas again through the use of pressure. The refrigerant (known as R-410A) begins the cycle as a low-pressure, low-temperature gas. It enters the outside unit where it's first compressed into a high-pressure, high-temperature gas. Next it enters the condenser's coil where the fan cools the gas into a high pressure liquid. The liquefied refrigerant flows through tubing inside your home to the HVAC unit. There it first enters the expansion valve which limits the flow of the liquid as it enters the evaporator. This valve lets the liquid expand inside the evaporator coil into a gas, chilling to about 7 degrees Celsius as air from the HVAC blower moves over the coil. The refrigerant then heads back to the outside unit as a low-temperature, low-pressure gas to begin the cycle again.

Air is cooled by being blown over the chilled coil, and it's then circulated throughout your home. The AC system continues running until the desired temperature is reached. Any humidity in the air condenses onto the coil as water and drips into a condensation pan. In this way, your home is both cooled and de-humidified by a central air conditioning system. Choosing the correct size of your air conditioner is a key a factor for setting up a home cooling system. Sizing an air conditioner requires a consultation with a professional Energy Management Consultant who looks at the factors that effect your home's cooling: Likewise, it's not a simple matter of dropping-in any air conditioning system. The size is very important because the correctly sized air conditioner should run a proper full cycle and ensure your home stays cooler longer. An over-sized AC system will quickly over-cool the air in your home and shut off too soon. However, the building structure itself (walls, wood, furniture, etc.) will not be cooled adequately and allow heat and humidity to creep back in, and the AC will kick-on again and again.

As a consequence, over-sized systems run for too short a time far too often. And it can cost you far too much. An undersized system, however, will not effectively cool your entire home. It will run continuously, waste energy, and wind up costing you more. Air conditioner sizes are rated in tons of cooling capacity. One ton of cooling is equal to 12,000 BTU's (British thermal units) per hour. For example, a typical residential unit is a 2-ton unit that cools 24000 BTU/hour and a larger 3-ton unit cools 36000 BTU/hour. While two air conditioners be the same tonnage, they could be completely different in terms of their energy efficiency or Seasonal Energy Efficiency Ratio(SEER) . Once you have found the right tonnage-size to cool your home, you'll want to look over which ones have the best SEER rating as is practical within your budget. The higher the rating, the less energy it will use - roughly 5% less per SEER. So an older 12 SEER upgraded to a higher efficiency SEER 16 will be approximately 20% more efficient and will cost less to run.