by DAN JAPE of RELIABLE HEATING & AIR originally published July 2008
In the thirty years I have been repairing air conditioners in the greater Atlanta area, this is one of the most asked questions from frustrated, hot homeowners And the answer is usually lack of tonnage or capacity and lack of proper airflow.
The capacity or tonnage of your air conditioner is the measurement of it’s ability to move heat from inside your home to the outside of your home. Air conditioners are produced from 1.5 ton to 5 ton in half ton increments. A ton of air conditioning is 12,000 Btu’s and a Btu is the amount of heat required to raise the temperature of one pound of water one degree in one hour or lower it one degree in your cooling system. A Btu is about the same amount of heat generated by burning one stick match. The tonnage of your system is picked by your heating cooling installer using a number of criteria such as sized of your home, insulation in your home, the amount of and type of glass in your home, the roof color, the amount of shade, which way your house faces and a number of other qualifiers that help determine the size needed to overcome the “heat gain” in the summer. The more tons an air conditioner is, the more expensive it is, so many times the builder of your home uses a unit that is not large enough to remove the heat properly in the summer. An air conditioner can’t be sized too large because it will not remove the moisture in your home, but it need to large enough to cycle off and on and maintain your desired temperature. Often when replacing an old cooling system, a slightly larger unit is needed to accomplish this goal. People often spend days researching the SEER rating of an air conditioner and the brand of the units available, and do nothing about what ton cooling unit to purchase. There is nothing more efficient than an air conditioner that is not running. A properly sized air conditioner will cycle off and on all but the hottest days of the year. Then it should be able to maintain a reasonable inside temperature.
Inadequate airflow from your supply vents can be the cause of both poor heating and cooling performance and with the advent of complete ducts system constructed of flex ducting with many twists and turns, many homes today have very little air delivery. Airflow in older homes with all metal ducting was far superior to the modern home of the last 15 years and often times there is very little that can de done about this due to the fact that this flex duct is sealed up behind sheetrock walls and ceilings. Many times it is not cost effective to replace all the ducting in your home with new proper metal ducting or properly installed flex duct. The airflow for your home originates with the furnace blower and it is often a good idea to increase the size of the furnace blower “drive” to help deliver more air to the remote rooms in your home. A variable speed blower furnace will also help deliver the correct amount of air without the need of spending thousands of dollars on duct modifications.
A few small adjustments when replacing your furnace and air conditioner can result in thousands of dollars of energy savings and enhanced comfort for years to come.