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How Many Tons Do I Need for an Air Conditioner?

Whether you want to install a window unit to cool a single room or are replacing a central air conditioning unit which cools the whole house, it is good to remember that bigger is not necessarily better. An air conditioner that is bigger than is required will not only have a higher initial cost, it could cost you more by short cycling. Of course, a unit that is too small can quickly run up your energy bill by running constantly in a futile attempt to keep the area comfortable.

Manual J

The Air Conditioning Contractors of America is the industry organization responsible for developing a method for calculating residential cooling loads. The result is the Manual J. Professional contractors should use it to determine the proper size of any home air conditioner they plan to install. Manual J takes into account numerous factors including the average geographical temperature, type and amount of insulation, ceiling height, exterior construction materials, and square footage.

Homeowner Calculations

Most do-it-yourselfers don't have access to Manual J, nor to the sophisticated tools available to professional installers. Still, armed with a tape measure and hand-held calculator, most people can make a relatively accurate estimate of their cooling needs. The process is simple--measure the length and width of the room to be cooled and multiply the two factors to get the square footage of the room. Repeat the process for each additional room that is to be cooled and add all of the sums together to get the total square footage that requires cooling. You can then compare this square footage to a BTU chart such as the one found on the Energy Star website:

Square Feet BTUs per Hour
100 - 150 5,000
150 - 250 6,000
250 - 300 7,000
300 - 350 8,000
350 - 400 9,000
400 - 450 10,000
450 - 550 12,000
550 - 700 14,000
700 - 1,000 18,000
1,000 - 1,200 21,000
1,200 - 1,400 23,000
1,400 - 1,500 24,000
1,500 - 2,000 30,000
2,000 - 2,500 34,000

These base BTU numbers will need to be adjusted to account for the specific features and circumstances of the room you are looking to cool.

  • High ceilings: If your room has a ceiling that is 10 feet high, you will need to increase your BTU total by 10 percent.
  • Hotter climates: If the climate where you are located is consistently hot or humid, add 10 percent to your BTU total.
  • Number of occupants: If the room you are looking to cool is usually occupied by more than one person, add 10 percent for each additional person. For example, a room typically used by four people will need a 30 percent higher BTU total.
  • Sun exposure levels: Does your room typically receive constant sun exposure during the day? If so, add 10 percent to your BTU total. If it does not receive any sun exposure, subtract 10 percent instead.
  • Kitchens: Add 600 BTU to your total to account for a kitchen.

BTU to Ton Conversion

A ton of HVAC cooling capacity is equivalent to the cooling effect of a ton of ice melting over a 24-hour period. However, most air conditioning units today are measured in British Thermal Units (BTUs), so a little conversion math will be required. Twelve thousand BTUs is roughly equivalent to 1 ton of cooling capacity. A well-insulated room with 100 square feet will require a 4,000 to 6,000 (a half ton) BTU air conditioner while a 12,000 BTU (one ton) unit can cool up to 500 square feet. A 2-ton (24,000 BTU) central air conditioning unit can effectively cool a 1500 square-foot residence.

Questions? Call GMC Air Conditioning Services

At GMC Air Conditioning Services, LLC, our HVAC professionals are NATE Certified and understand the complexities of central air conditioning systems. Whether you need your air conditioner repaired or replaced, call our experienced team at (954) 266-0750.

Source: eHow