Your Home
In January of 2006, the government helped consumers cut the cost of cooling by raising central air conditioner efficiency standards a whopping 30%. All air conditioners manufactured after January 23 of 2006 must meet a minimum SEER (Seasonal Energy Efficiency Ratio) of 13, compared to a 10 SEER requirement in effect since 1992. Units manufactured before 1992 are even less efficient. In 1981, when SEER ratings were first used, efficiencies were about 7.8 for central air units and 7.51 for heat pumps. Any units still operating built prior to 1976 are assumed to be between 6 and 7 SEER.
Air conditioners and heat pumps are rated by their hourly cooling capacity, expresed in BTUs and popularly referred to as tons of cooling with 12,000 BTUs per hour translating to one ton of cooling.
This table will give you an idea how of much you can save in seasonal cooling costs by choosing a central air conditioner or heat pump with a higher SEER. The table is only an approximate comparison of systems with similar cooling capacities and different SEER ratings under similar circumstances. Your actual operating costs will vary with your home's construction, thermostat setting, and lifestyle.
| Air Conditioner Shopping Guide | ||||||
|---|---|---|---|---|---|---|
| Central Air Conditioning Efficiency Table | ||||||
| Annual Operating Cost per SEER | ||||||
| BTUs/Hr. | SEER | |||||
| 10 | 11 | 12 | 13 | 14 | 15 | |
| 24,000 | $426 | $389 | $357 | $331 | $308 | $288 |
| 30,000 | $528 | $482 | $443 | $410 | $382 | $357 |
| 36,000 | $630 | $575 | $528 | $489 | $455 | $426 |
| 42,000 | $732 | $667 | $613 | $568 | $528 | $494 |
| 48,000 | $833 | $759 | $698 | $646 | $601 | $562 |
| 54,000 | $934 | $851 | $782 | $724 | $674 | $630 |
| 60,000 | $1,034 | $943 | $866 | $802 | $746 | $698 |
| 1,400 Cooling Degree Days, 23 Deg. Design Temperature Difference | ||||||
| 2006 estimated costs based on avg. cost per kWh. | ||||||
When talking with contractors about replacing your central air conditioner or heat pump, be aware there are other features besides SEER that might affect a unit’s efficiency. Variable speed heat pumps and air conditioners, or units with two stage compressors are more efficient than single speed or single stage units.
If your heating system could also stand replacing, now would be a good time to consider replacing your heating and cooling system with a heat pump. A heat pump is basically a reversible air conditioner. Both move heat from one area to another. In winter, a heat pump does this by capturing heat from the outdoor air and moving it inside. Even more efficient heat pumps, called geothermal or simply geo heat pumps, capture heat in winter from a heat sink such as the earth or a body or water. A water/antifreeze solution is circulated through a closed pipe loop to move the heat around. In summer, the process is reversed, moving heat from your house and dumping it in the heat sink .
If you've made energy efficiency improvements to your home (such as additional insulation, storm windows and doors, or low-E double pane windows) and plan to replace your air conditioner, encourage your contractor to size the unit correctly using a heat loss/heat gain calculation rather than using the "rule of thumb" method or simply replacing your old system with a new one of the same capacity. The same rationale applies for homes built within the last 10-15 years, which are generally more energy efficient than the "rule of thumb."
The "rule of thumb" sizing method could mean less comfort, not more, for more energy efficient homes because the units end up being oversized. Oversized units in summer cause "short-cycling," cooling your home quickly but not operating long enough to properly dehumidify the air.
In areas of relatively low humidity like ours, short-cycling doesn't give a cold evaporator coil enough time to remove moisture. Consequently, indoor humidity can increase with each cycling of the air conditioner, leading to a cold, clammy feeling. That's not comfort. Besides, it's hard on the compressor and shortens equipment life.
So that you know, the old rule of thumb was that a home needed a ton of cooling (12,000 BTUs) for every 500-600 square feet of living space. Again, encourage your contractor not to use this method if you've made significant energy efficiency improvements or if your home was built within the last 10-15 years.