The ABCs of buying an AC

If you are considering purchasing or upgrading your home’s air conditioning unit, finding one that correctly fits your cooling needs will give you energy-saving relief from the summer heat. Here are a few things to keep in mind before investing in a central air or room air conditioning unit.

A central air conditioning unit is an excellent way to cool the home, though it is accompanied by considerable upfront cost when compared to a room air conditioning unit. Central air units are a quiet, efficient and effective way to cool more than one area of the home, making these units popular among homeowners. Consider a unit with a high seasonal energy efficiency ratio (SEER) for the best energy-saving results. Those made after Jan. 23, 2006, must have a minimum SEER rating of 13. The SEER rating of an air conditioning unit measures the cooling capacity (in BTUs per hour) to the power input (in watts).  A unit with a higher rating generates more for less energy.

When researching or shopping for a central air conditioning unit, remember these additional points:

  • Find a unit that matches the cooling needs of your home. A unit that is too large will not remove humidity as well as one that is the proper size. Those too small will not effectively cool your home.
  • Install the unit on the north side of your home. It will work more efficiently than a unit that is placed where the sun will heat it.
  • Properly install and insulate ductwork. This will ensure you get the most out of your air conditioning unit.
  • Read the EnergyGuide label. It will show you how much energy the unit uses and make comparison shopping easier.
  • Consider an upgrade if you already own an older central air unit. Those available today can run upwards of 40 percent more efficiently than those produced just a decade ago.
  • Some systems, such as heat pumps, provide both hot and cold air depending on the season. A qualified contractor can help you decide if a stand-alone air conditioner or a dual-purpose system is more appropriate.
  • Replace or clean the filter often. Failing to do so can add unintended stress to the circulating fan or allow the evaporator coil to get dirty– both of which can reduce the unit’s efficiency and eventually lead to premature failure of the equipment.

Room air conditioning units are intended to cool a room or a number of rooms, rather than the entire home. They are ideal for apartments or for cooling a smaller, frequently-used area of your home like a living room.  Room air conditioners tend to be louder and take up more indoor space than a central air unit. Consider a unit with a high energy efficiency ratio (EER) for the best energy efficiency results, similar to the SEER rating mentioned above. If you know the square feet of the space you are cooling, you can match the BTUs needed with this useful table. Other shopping tips include:

  • Purchase a unit with an easy-to-access filter. Make sure to clean it regularly for continued, efficient use.
  • Find a unit with a digital temperature readout and built-in timer. These features will more conveniently assist you in running the unit only when necessary.
  • Purchase a unit that meets your home’s electrical system capabilities. Some units require more voltage or different electrical plugs to power them.
  • Compare EnergyGuide labels to determine which unit’s energy efficiency rating is within your budget.
  • Follow the installation instructions to ensure the unit works as designed. Keep in mind that many units need to be installed level to the ground for proper operation and drainage.
  • For best results, install the unit on the north side of your home. If installed near the corner of a room, look for a unit that can send the airflow in the direction it is needed.

Owning an air conditioning unit best-suited to efficiently cool your home will make the cost of running it one less thing to worry about.  Regular maintenance will safeguard its efficient operation in the years to come.

Some information provided by Energy Savers


BTUs needed per square foot
Area to be cooled
(sq. ft.)
Capacity needed
(BTUs /hr.)
Area to be cooled
(sq. ft.)
Capacity needed
(BTUs /hr.)
100 up to 150 5,000 550 up to 700 14,000
150 up to 250 6,000 700 up to 1,000 18,000
250 up to 300 7,000 1,000 up to 1,200 21,000
300 up to 350 8,000 1,200 up to 1,400 23,000
350 up to 400 9,000 1,400 up to 1,500 24,000
400 up to 450 10,000 1,500 up to 2,000 30,000
450 up to 550 12,000 2,000 up to 2,500 34,000

If the room is heavily shaded, reduce capacity by 10 percent.
If the room is very sunny, increase capacity by 10 percent.
If more than two people regularly occupy the room, add 600 BTUs for each additional person.
If the unit is used in a kitchen, increase capacity by 4,000 BTUs.

Information provided by Energy Star