There are many different efficiency levels and cooling capacities or “tonnage” of air conditioners available today, but all the different units can be divided into three distinct major types or categories; single stage, two stage and variable speed speed units.
Efficiency or SEER
The efficiency or SEER rating of an air conditioner refers to how much electricity that particular unit will consume to keep you cool in a season. SEER is an abbreviation for “seasonal energy efficiency ratio” and it tells you how much electricity an air conditioner will consume over a typical season. The higher the SEER the less electricity a unit consumes in a season.
Starting in 2007, the minimum SEER rating became 13. Before this, the efficiency levels went all the way down to 6 SEER or less. The actual savings every SEER number affords you varies, but on the average it is between 5 and 10 percent savings per larger number SEER selected.
Tonnage or Capacity
The ton of an air conditioner is a rating of the unit’s ability to remove heat from your home or business. A ton of cooling is 12,000 BTU’s and residential air conditioners are made in sizes of 1.5 ton to 5 ton in half ton increments. A BTU is a measure of heat which stands for British Thermal Unit and one BTU is equal to the amount of heat one wooden match puts out.
In other words, a 1.5 ton air conditioner will remove the amount of heat the 18,000 matches would emit if they were all burning at the same time. The reason it is called a ton is that is the amount of heat (12,000 BTU) it would take to melt one block of ice weighing a ton in one hour. The job of an air conditioning contractor is determining the correct size or tonnage of a unit for you, and in this case it is not a matter of the more the better.
An oversize air conditioner will not remove the proper amount of moisture from the air to give you the comfort you deserve. An undersized air conditioner will run constantly even at moderate temperature and will not adequately condition the space. There are some air conditioners you can slightly oversize and still get very good dehumidification and those are two speed and variable speed units. A variable speed furnace will also help in having a system that not only keeps you cool, but dry also.
Single Speed Air Conditioners
Single speed air conditioners produce the same amount of heat removal all the time regardless of how hot and muggy it is outside. They have to be large enough to cool you on the hotter days of the year and because of that, they are larger than needed on the moderate days. A good contractor selects a unit in the middle, as it is a bad idea to pick a unit sized that will handle a peak day when the bulk of the time we do not see peak temperatures.
This means that on a 100 degree day the unit will run constantly, but that is far better that picking a large enough unit to handle the few days it goes over a 100. Single speed units come in three different SEER ratings; 13, 14 and 15 seer. All these units can use any type of indoor furnace or air handler and they are 35 to 50 percent more efficient than most 15 to 20 year old units you might have in your home or business.
Two Speed Air Conditioners
Two speed air conditioners have two distinct output capacities to better condition your home. These units have the ability to change the amount of cooling capacity they produce depending on how hot it is. Because they can slow down and run longer, they do a better job of removing moisture and providing enhanced comfort.
A two speed air conditioner can run in low or high speed depending on the temperature outside that day. These units are very efficient and provide a high level of comfort and dehumidifcation.
Variable Speed Air Conditioners
Variable Speed units are the very best air conditioners available and provide extreme comfort and moisture removal unlike any other system available. Instead of turning off and on all day causing temperature swings along with hot and cold spots, a variable speed unit has 700 different outputs to accurately and efficiently provide temperatures to 1/10 of a degree of what is desired.
The Trane True Comfort variable speed units are also the quietest on the market and can barely be heard running. Coupled with a Trane variable speed indoor unit these systems can heat and cool a home for up to 60% less than an older unit and will take out 10% to 15% more moisture in the summer due to their extended run times at very low speed.