Bigger Isn't Necessarily Better
Once you've settled on the type of air conditioner you want, choosing the right size unit for your needs is very important. The size of most AC units is measured in terms of Btu's per hour, though some central AC units and heat pumps may also be rated for tons of cooling capacity (a ton is equal to 12,000 BTU per hour). Air conditioners are designed to cool a fixed amount of space efficiently. Oversizing a residential AC system by 50% will cause a 10% increase in energy consumption. Not only do oversized units consume more energy, but they also remove less moisture from your home.

The best way to reduce the required amount of cooling capacity, and the size and cost of the AC unit needed, is to tighten your home with caulk and weatherstripping and have it properly insulated.

Efficient Models Save Money
Along with the type and size, energy efficiency is an important consideration. Buying an inefficient model will guarantee high electric bills over the unit's lifetime, which could be many years.

Look for the yellow EnergyGuide label on all new AC units (Figure 16). For room air conditioners, these labels display the efficiency rating in terms of the unit's EER, or Energy Efficiency Ratio. This is a measurement of the AC unit's cooling efficiency based on the ratio between the cooling output (in Btu's per hour) and the electrical power input (watts). Most new room air conditioners have EERs of 9.5 to 10.5. An EER of 11 to 12 represents very high efficiency. EnergyGuides are useful for general comparison, but note that the stated energy costs may not accurately represent your energy costs as your AC usage and lifestyle and comfort zone may vary.

What's a SEER?
The SEER is a central AC unit's Seasonal Energy Efficiency Rating. Unlike the EER, the SEER estimates a unit's performance over an entire cooling season, rather than measuring its performance at a given temperature and humidity level. In short, it measures the seasonal performance of the unit based on the cooling accomplished (in Btu's of energy) divided by the electricity consumed (in kwh).

Btu's cooling provided
seasonal kwh comsumed

A minimum SEER of 10.0 for central air conditioners is required by the National Appliance Efficiency Standards. There is a wide selection of units available with SEERs up to 17.

You can save a lot of money and energy by upgrading an older, less efficient system. For example, by replacing a 1970s vintage central air conditioning unit (SEER = 6) with a new unit having a SEER of 12 should cut your air conditioning costs in half.

Depending on the use, cost of electricity and the temperature, these savings can actually pay back the cost of a new system within a few years. In general, central AC systems are more efficient than room AC units. Once again, however, an oversized system will waste money and energy.

Shopping Tips
It's a good idea to ask your neighbors and friends with a similar lifestyle and home style about their systems; how long they've had them; and how much they cost to run. Check the consumer review publications at your local library, as well as your local utility, to find the most energy efficient models. Then shop around for a reputable air conditioning contractor to install a central AC system, or a reputable dealer for a room AC unit. If you're having a central system installed, get bids from three or more contractors and check their references.

Disposal and Recycling of Your Old AC Unit
In the past, discarded appliances were often dumped in landfills or even in ditches and creek beds. Very few were recycled and the hazardous materials in discarded appliances contaminated the soil and ground water. Today appliances must be disposed of in accordance with state and federal guidelines. In particular, refrigerators and air conditioners require special handling during the disposal process.

This is because the refrigerant used in these older appliances contain CFCs (chlorofluorocarbons). Once released into the atmosphere, CFCs damage the ozone layer that shields us from the sun's radiation. Since 1989, CFCs have been phased out and banned throughout the industrial world, and all new refrigerators and AC units must use non-CFC refrigerants.

Disposing of an air conditioner involves the careful removal of CFCs by a certified technician. The oil from the compressor crank case also needs to be removed. The motor and copper tubing can then be removed for separate recycling. AC units manufactured before 1978 may have oil-filled capacitors contaminated with toxic PCBs (Polychlorinated biphenyls), a substance now banned in the U.S.. These components must be removed and taken to a hazardous waste facility before further processing can occur. Finally, there may be temperature gauges and switches that contain small amounts of mercury, another extremely toxic substance. Once these hazards are removed, the remaining materials are segregated and recovered according to the recyclability of their materials.

If you have an old AC system that you want to dispose of safely, contact the Iowa Department of Natural Resources at 1-800-367-1025 to find the nearest qualified disposal company. Forty-three Iowa counties have solid waste disposal companies that can handle appliances.