Two of the basic measurement standards for air conditioners are British Thermal Units (BTU) and tons. It takes one ton of air to move 12,000 BTUs of heat per hour. When you shop for an air conditioner, a common starting point is to determine the number of BTUs you will require and then calculate the corresponding number of tons you need. Use this information as a basis for getting an on-premise customized estimate based on your home size and many other factors from a licensed air conditioning installer.

## Two-and One-Half-Ton Air Conditioner

A 2.5-ton air conditioner will move 30,000 BTUs of heat per hour. You can confirm that you have a 2.5-ton air conditioner by looking at the metal manufacturer's identification plate on the back of the air conditioner. The model number will include the number 30, identifying the unit as having a 2.5-ton capacity. Residential air conditioners typically range from one to five tons. Therefore, a 2.5-ton air conditioner is about in the middle of the standard range for residential air conditioners.

## Three-Ton Air Conditioner

A 3-ton air conditioner will move 36,000 BTUs of heat per hour. To confirm that you have a 3-ton unit, look for the number 36 on the metal manufacturer's identification plate on the back of the air conditioner. A 3-ton unit is a bit past the middle of the standard range for residential air conditioners.

## Similarities

Whether you decide on a 2.5-ton or a 3-ton air conditioner, you'll find a wide array of styles to select for keeping your home cool and comfortable. If you are shopping for a central air conditioning system, your choices include a single-stage or two-stage unit or a condensing air conditioner. There are also 2.5-and-3-ton-capacity wall units, portable units that you can move from room to room and ductless "package systems" that combine the compressor and the condenser all in one. The SEER ratings (Seasonal Energy Efficiency Rating) will also be similar, and you will easily find models with ratings that range from 13 to 17.

## Differences

The costs of the air conditioning unit and costs of cooling are the biggest differences between 2.5-ton and 3-ton units. Don't think that by going bigger you will feel a difference in the level of cooling. Your decision should be based solely on the BTU capacity that you need to cool your home properly. Once you know your BTU requirements, you will have a basis for making a good decision.

## Energy Cost Comparison

To get an idea of the energy cost differences, let's assume the air conditioner is to be used in Atlanta, Georgia; the average cooling hours are 1,200 for the year; the air conditioner has a SEER rating of 17; and the cost per kilowatt hours charged by the utility company is 7 cents. The math formula is as follows: air conditioner BTUs, multiplied by cooling hours, divided by SEER rating, multiplied by the cost per kilowatt hours and divided by 1,000. As a result, the cost per year to operate the 2.5-ton air conditioner would be $148.23, and the cost per year to operate the 3-ton air conditioner would be $177.88 -- about 20 percent higher.