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Question DetailsAsked on 1/13/2016

What is SEER and EER in HVAC

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SEER is the Seasonal Energy Efficiency Ratio, EER the Energy Efficiency Ratio. SEER is more commonly used to compare A/C units these days. Basically, both are a ratio of the amount of cooling (heat removal) you get divided by the electric energy required to achieve that - so a common 13 SEER unit (generally the minimum allowed today in US) removes about 13,000 BTU of heat for every 1000 BTU worth of electric energy the compressor and cooling fan use to do it.

SEER is figured based on a simulated seasonal variation of temperatures - sort of like the EPA uses simulated driving testing to estimate new car gas mileage. EER is based on a constant inside and outdoor temperature and humidity. Generally speaking, about 11 EER = 13 SEER on average. The difference between the two is not real important for residential use - just be sure you are comparing the same type of number (SEER or EER) when comparing units - ALL units have to have SEER ratings by law, so use that one.

Heat Pumps (which can both cool and, down to maybe 35-42 degrees outdoors temperature, heat also (without using their auxiliary electric heating coils that are needed when it is cooler outside), have both a SEER (for the cooling cycle) and a HSPF (Heating Seasonal Performance Factor) rating, which is a similar number for the heating season.

For the difference in energy usage between different SEER ratings, divide the smaller by the larger SEER rating to estimate what percentage of the electricity the more eficient unit will use. For instance, a 15 SEER unit will use 13/15'ths (87%) as much electricity as a 13 SEER unit, while a 20 SEER will use 13/20 (65%) as much. Local power utilities and the EPA commonly have estimated annual A/C cost numbers on their website broken down by type of appliance usage. So say your electric utility says A/C for normal (2000SF) house with 13 SEER unit in your area is $1500/yr in electricity (a common range for much of the deep South for instance), a 15 SEER unit would use 87% as much power or about $1305, or about a $200 savings per year over a 13 SEER unit. A 20 SEER would use 65% as much or $975, a savings of about $525/year. Assuming a 10-15 year life for the unit, a 15 SEER unit would therefore have to be not more than $2-3,000 more expensive in this case to be beneficial to you (assuming electric rates stay the same in the future), or a 20 SEER unit not more than $5200-$7900 more expensive. For a high-use area like this example, a unit in the higher efficiency range can be beneficial, while in an area with only a few hundred to maybe $600/year A/C energy cost it would take either a much longer time to pay off (Assuming the unit lived that long), or a more efficient unit could not have as high an up-front cost premium and still be economic.

Now the caveats which make units above about 15 SEER uneconomic in all but the most severe A/C environments - first, the above assumes no time value on the money spent on the unit - either loan interest to pay for it, or lost interest/dividends on money you take out of savings to pay for it up front. That factor alone commonly kills any benefit from higher efficiency units in all but the most severe A/C environments. It also assumes you will live in the house for the life of the A/C unit - unlikely since the average homeowner moves every 5-6 years. Taking those factors into account, generally a higher SEER rating than the 13 or 14 that the law requires (depending on your area) pays off only in very severe (hot desert or extreme high humidity and high temp year around) environments.

Here is a link to a map showing what efficiency units are required in various areas of the country -

Here is a prior question with several answers that explains it in a bit more detail, if interested -

Answered 4 years ago by LCD

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