Choosing the right size Central Air Conditioner
As with sizing furnaces or boilers, it is important to have an HVAC Contractor perform a load calculation before you decide which size air conditioning system to buy. If you install an air conditioner which is too large, it will cycle on and off too often, substantially reducing the efficiency of the system. Too small, and your air conditioner may not be able to meet the demands of a hot, humid day.
The industry standard load calculation is called the Manual J calculation. It takes into account the size of your house, the amount of insulation installed, the square footage, and a host of other factors.
SEER ratings
SEER (Seasonal Energy-Efficiency Rating) is a comparative indicator of an air conditioner’s efficiency. The typical central air conditioning system of the early 1990s had a SEER of about 6. It rose to 10 early in this decade. All central air conditioners manufactured since January 23, 2006 must have a SEER of 13 or higher. Older unsold units were grandfathered under this government regulation. At this point, if any of those units are still available, they represent false economy. Guides that recommend them as a budget alternative are out of date. Current central AC units have SEER ratings that range from 13 to 23. The rating can be easily understood as a percentage. For instance, a 14 SEER air conditioner is 40 percent more efficient than a 10 SEER air conditioner.
Capacity and efficiency are major factors in the price of an air conditioner. A more efficient unit costs less to operate. We found worksheets for estimating how much, but electricity prices throughout the United States change often and usually rise. If you currently have gas or oil heat and a central air conditioner, you can compare your summer and winter electric bills to get an idea of how much more electricity you use during the summer.
Air ConditionerExperts say the average life of a central air conditioner is 15 to 20 years. If yours is that old, they say the break-even period is short if you replace it because your new system will be much more efficient by default. When announcing the current SEER standard, Energy Secretary Samuel Bodman asserted, “Homeowners who choose to buy more energy-efficient air conditioning systems will realize significant savings in their energy bills and greatly reduce their energy use.” The Rocky Mountain Institute encourages, “Buy a new air conditioner if your existing model is more than ten years-old, as such models are often only half as efficient as contemporary models.”
The value of efficiency much beyond 13 SEER is somewhat controversial. Government and environmental organizations advocate for the highest efficiency you can afford. The American Council for an Energy-Efficient Economy (ACEEE) recommends SEER of at least 14.5. The professionals at AllExperts.com disagree about the value of high-efficiency air conditioners. Some point out that more expensive units may have other virtues, such as a longer warranty. The majority of experts believe that a 13 SEER air conditioner is the best value for most people (but see the Rebates section below). If you can afford greater efficiency, however, you will use less electricity and make a contribution to the environment, but you may not recoup the extra cost in energy savings. Be aware that experts say an air conditioner must be connected to an appropriate coil to achieve the published SEER specification. If you are replacing an existing system, make sure you get a new coil.
