What Will a Central Air Conditioner Lower the Inside Temperature of My House To?

Basics

• The temperature produced by a central air conditioner depends on the temperature of the air going into the system, which in turn depends on the outside air temperature. However, the unit can typically lower inside temperatures to between 18 and 20 degrees below the outside temperature. This means that if it is 80 degrees Fahrenheit outside, the air conditioner can lower the temperature to between 60 and 62 degrees Fahrenheit. On mild or very humid days, the temperature drop is smaller at around 15 to 17 degrees Fahrenheit cooler than the outside temperature.

Testing

• You can test your central air conditioning system to ensure that it works according to specifications. First, make sure that the outside temperature has stayed above 60 to 65 degrees Fahrenheit for at least 48 hours -- running the unit at temperatures below 60 degrees Fahrenheit may damage it. Set the fan to “Auto” and then set the thermostat below the current room temperature. Both the fan and condenser should come on almost immediately. Run the unit for at least 10 minutes to balance the temperature in the ducts.

Checking

• Check the temperature in both supply and return vents. The temperature at the supply vent should be from 14 to 20 degrees cooler than either the current room temperature or the temperature in the return registers. If the temperature difference is over 20 degrees, you may have a dirty filter, incorrectly sized or routed ductwork, or a fan that is incorrectly sized or not functioning properly. If the difference is under 14 degrees, you may have a dirty coil, a compressor that needs maintenance, a fan that is too big, a return air system that is not working or a refrigerant loss.

Suggestions

• You can maximize the ability of your central air conditioner to lower temperatures while efficiently using energy. Install it in an area that is shaded or otherwise protected from sunlight. Add a programmable thermostat that can adjust temperatures based on room use and outside climate. Insulate all interior spaces to minimize the loss of cold air. Seal windows and other cracks to avoid leaks. Close vents, doors and fireplace flues in rooms that are unoccupied.