Towards More Efficient Central Air Conditioning
If you have an older central air conditioner, you might be able to reduce the energy you use to cool your home by 20-50% by taking the following steps and installing a new, more efficient model.
 First, take as many of the steps on the preceding pages of this section as you can to tighten up your house and lower your need for air conditioning. Now you're ready to choose the most efficient system for you.
The next step is very important: get the right size unit for your needs. If you install an oversized system, it will run for short periods. This additional cycling on and off will increase your electricity use (and your bills) and decrease the unit's overall efficiency. An oversized unit also won't dehumidify as much as a correctly sized one so you won't feel as comfortable.
The best way to get the right sized unit for you is to ask a qualified air conditioning technician or energy auditor for a thorough analysis, which will include local climate information and calculations of heat gain through your windows and walls. Be sure to tell your technician or auditor about all the steps you have taken to lower your need for air conditioning. Whatever you do, don't accept the simple rules-of-thumb used by a salesman to calculate how big a system you need. You will end up buying a bigger system than you need. So you'll pay more for the bigger model and for your bigger electric bills.
Now comes the easy part--buy an air conditioner that has an EnergyStar® label. It will be more energy efficient than the other models.
If you want to know the details, look for the SEER ratings. This stands for "seasonal energy efficiency ratio" or the seasonal cooling output in British thermal units (Btus) divided by the seasonal energy input in watt-hours for the average U.S. climate.
Think about this when deciding whether to buy a new central air conditioner. In 1988, the average model had a SEER of around 9. Older models ratings could go as low as 7 or even 6. The national standard currently requires a minimum SEER of 10. Those EnergyStar® labeled models have a SEER of 12 or higher. So buy a model with a SEER rating over 12, making sure it is the right size for you. You will end up making back any higher price in just a few years (or less) of lower electricity bills.
Additional energy-saving features you will want are: (i) a fan-only switch to use to ventilate your house at night for big savings over using the air conditioning; (ii) a filter check light which tells you when it is time to check the filter; and (iii) an automatic delay fan switch which turns off the fan a few minutes after the compressor stops.
Those of you who live in humid climates will also want a model that is effective at removing moisture and includes a variable-speed or multispeed blower. Running the unit on a lower speed will reduce your efficiency somewhat but will dehumidify your home more, so use the lower speed only on very humid days. You can get a model with a variable-speed blower that is controlled by a humidistat, which automatically changes fan speed according to the current humidity.
| 
