Sometimes it’s hard to keep all the acronyms in the HVAC (there’s one right there!) world straight. There’s BTU, MERV, IAQ, BTUH, AFUE, ECM, HEPA, RH, and dozens more. So 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.
First, A Little History
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 (ARI—there’s just no escaping all those acronyms!) 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.
As long as we’re talking acronyms, BTU or British Thermal Unit has been with us since...well, forever. It’s a measurement of heat, similar to a calorie. To give you an idea of how much heat a BTU is, imagine a wooden match burned end to end. While burning, it gives off roughly one BTU. The HVAC world mostly uses BTUH, or BTUs per hour: BTU output over a 60-minute period.
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.
The Evolution of SEER
In 1987 SEER, Seasonal Energy Efficiency Ratio, was introduced as the new rating. As before, the rating is verified by a third party (now it’s AHRI, Air Conditioning, Heating and Refrigeration Institute, which now includes furnaces). And, it’s still the higher the number, the better. But now the rating is more accurate over a wide range of operating conditions, including lower efficiency conditions like the first five minutes of operation. (Just like your car, it takes a few minutes to get everything working up to peak efficiency.)
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 contactor 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.