When shopping for a new central air conditioning system, it is important to buy the most energy-efficient equipment you can comfortably afford. But don’t rely on stickers that claim a unit is “energy efficient.” Knowing the SEER rating will help you judge just how energy efficient an air conditioning unit is.

What Is SEER?

SEER stands for Seasonal Energy Efficiency Ratio. It may also be called a Seasonal Energy Efficiency Rating. This is the ratio of the cooling output of an air conditioner over a typical cooling season, divided by the energy it uses in Watt-Hours. A Watt-Hour is a unit of measurement for power over an hour-long period.

“A SEER ratio is calculated over an entire cooling season using a constant indoor temperature and outdoor temperatures ranging from 60 degrees to more than 100. This simulates a typical season,” explains Richard Rojo of Rosie on the House Certified-Partner, Trane.

Benefits of a High SEER Rating or Ratio

Higher Energy Efficiency:

The SEER ratio is a maximum efficiency rating, like the miles per gallon for your car. For example, say your car gets 28 miles per gallon on the highway. But when you are stuck in city traffic, it's a lot less efficient. The same goes for your air conditioner. If your SEER ratio is 21, that's the maximum efficiency, but it could be lower depending on conditions. The higher the SEER of your air conditioning system, the more efficient it is.

A higher SEER rating provides greater energy efficiency in certain conditions. The minimum standard SEER for air conditioners is 13, though most modern air conditioners have a SEER that ranges from 13 to 21. Trane air conditioners range from 14.5 SEER up to 22 SEER. Keep in mind this rating is a maximum. The efficiency of your system can vary based on the size of your home, your current ductwork, and other variables. Even with a high SEER rating, it’s still helpful to use other energy-saving tips for the summer season.

The U.S. Department of Energy enforces minimum SEER requirements that differ by geographical region. The minimum in the Southwest is 14. A 13 or 14 SEER rating doesn't necessarily mean a unit is inefficient. Most older AC systems are rated at around 8 or 9. So even the lowest available SEER-rated system you buy today will be much more energy-efficient.

“You can get AC systems with higher SEER ratings; in fact, they go all the way up to 26 SEER. But don't do it without updating your ductwork. Even the most energy-efficient unit will underperform if you couple it with bad ducts,” warns Rojo.

Greater Indoor Comfort:

Getting an air conditioning system with a higher SEER does mean you will be more comfortable in the summer months, especially in a hot region like Arizona. Higher SEER units often have two components that provide greater indoor comfort.

Two-stage or variable-speed compressor.

Variable-speed blower.

Air conditioners with lower SEER ratings are usually single-stage and only run on one speed. This means they will frequently turn on and off during mild weather and you will experience uneven cooling or hot and cold spots. You will also experience higher humidity levels which makes it feel hotter than it actually is. The AC needs to run for a long time to remove humidity from your home's air. The ups and downs of a single-stage system don't accommodate for this.

“There’s no magic SEER number. Anything over 13 is great,” says Rojo. “Because if you have an old 8 SEER system and replace it with a 16 SEER unit, you could significantly reduce the cost of cooling your home.”

Consider the level of energy efficiency that is important to you, and whether you can afford to buy both a new air conditioner and new ductwork. Rojas says it could be better to put in a 14 SEER unit and fix your ductwork than to buy a 19 SEER AC and lose the extra efficiency through bad ducts.

Tax Credit & Rebates:

Don’t forget to look at tax credits and manufacturer’s rebates that can bring down the cost of a high SEER system. If you have an old system and you upgrade it to one with at least 13 SEER, you likely be more comfortable in your home, plus, your electric bills will be lower during air conditioning season.

A 16 SEER system could be even better in your home. Check with your utility company as SRP, APS, TEP, and Trico may offer rebates on some of the higher efficiency systems.

Research what you should look for in a SEER rating and how a higher rating will impact your costs and comfort level. Consult with a trusted air conditioning professional, such as Trane, before selecting a new AC system for your current home or when building a new energy-efficient dream home.

For more do-it-yourself tips, go to rosieonthehouse.com. An Arizona home building and remodeling industry expert for 35 years, Rosie Romero is the host of the Rosie on the House radio program from 8 a.m. to 11 a.m. Saturdays on KTAR-FM (92.3) in Phoenix; KGVY 1080AM 100.7FM; 10 a.m. to 11 a.m. on KNST-AM (790) in Tucson.