What’s this SEER rating all about? Well, SEER stands for Seasonal Energy Efficiency Ratio and it’s the standard measurement of efficiency for air conditioning systems. Here’s more about SEER, how it works, and how it came to be today’s standard.

The History of SEER

Before there was SEER, there was EER – Energy Efficiency Ratio. Back in the 1980s, EER was a rating of cooling capacity as compared to the energy consumed by the air conditioner, expressed as BTUs per watt. The rating was third-party verified by the Air Conditioning and Refrigeration Institute to keep everyone honest. The larger the EER number, the better. Obviously 8 BTUs per watt is better than 7 BTUs per watt. An EER of 8 vs. 7 means 14% more BTUs for the same watt of energy consumed.

The original EER was like the EPA rating on your car for highway use. It was calculated using steady operation – no starts and stops. But start up and stopping weighs heavily on the efficiency of any mechanical device. So the government decided to adjust the rating to account for those variances in starting and stopping.

Understanding SEER

Today, SEER is an efficiency rating for air conditioners and air conditioning systems as deemed by the Air Conditioning, Heating, and Refrigeration Institute (AHRI).

Keith Hill, technical support manager at Minnesota Air, explains it as the annual average of the amount of cooling BTUs generated by the system for each watt of electrical energy consumed. Put simply, a SEER rating is determined by looking at the amount of cooling produced – or heat energy moved from inside to the outdoors (BTUs) – divided by the amount of electricity used (watts). Products with higher SEER ratings are more efficient.

“SEER comparison can be used to accurately estimate savings when you are in the market for an upgrade,” says Keith. “Your new system SEER divided by the old system SEER is a very accurate estimate of how much you will save.”

For example, if your new model is 16 SEER and your older model is 10 SEER, you divide 16 by 10 to equal 1.60. Put in percentages, that means your new system will provide 60 percent more BTUs into the home than the old system for the same electrical energy used, he says. 

Proper SEER Achieved By Proper Installation

Keith reminds homeowners that a SEER value is only achieved if the whole system is replaced. That means you need the outdoor unit to be at the same SEER rating as the indoor unit in order to have it operate at peak efficiency.

“Some would have you believe that they can replace only the outdoor unit and you will realize the rated SEER value, but there is no rated SEER value on just the outdoor unit,” he says. “A new outdoor unit with an old indoor unit (A-coil or evaporator coil) is an unknown – there is no way of knowing what the system efficiency will be.   

He suggests getting the rating in writing to make sure you are getting what you are paying for – either the manufacturer’s specification sheet or a certificate from AHRI. Most utilities require a certificate from AHRI before they issue an efficiency rebate, but as a buyer, you should too.

 Another important item to understand about SEER ratings is that you really need to get it installed by a professional who knows what they are doing in order to achieve that rating. The technician should not only install it correctly with the rated airflow, but also the proper refrigerant charge, Keith says.

“System efficiency can be affected by as much as 25 percent if the refrigerant charge is off by 10 percent. This is why you hire a pro that has the training and the credentials to prove it.”

Buyer Be Aware

With split systems – central air conditioners and heat pumps – there is a potential “gotcha.” The two major components must be “matched” to achieve the advertised SEER rating. The outdoor unit and the indoor coil must be an AHRI-matched combination. Your contractor or installer should be able to provide you with a certificate that shows the specific model of both components and the resulting rating.

An unscrupulous contractor could try to sell you a high-efficiency air conditioner while using your existing coil. Or, sell you an inexpensive new coil and tell you it’s matched to the higher SEER value. But in both cases you’d be getting something less efficient. It may work just fine, but it will not be what you paid for. If the components are matched, there's a certificate available – always ask for it.

Do You NEED A Product With A Higher SEER Rating?

Most basic AC models sold today have much higher SEER rating compared to the basic models from a few decades ago. In fact, according to the Department of Energy, “today's best air conditioners use 30% to 50% less energy to produce the same amount of cooling as air conditioners made in the mid-1970s. Even if your air conditioner is only 10 years old, you may save 20% to 40% of your cooling energy costs by replacing it with a newer, more efficient model.”