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SEER versus EER Ratings, Equipment Derating, and Your Wallet

Many consumers hear from HVAC retailers about SEER ratings on air conditioning equipment and think that by investing in high-dollar equipment they'll get the best performance and energy savings available. But spending more for higher rated equipment isn't always the right option for consumers who are interested in optimizing their system performance and reducing costs. Retailers often shy away from sharing the gritty details about energy savings versus the cost offset for higher SEER rated equipment, and, more than that, they fail to educate consumers about equipment derating.

So what is the difference between EER and SEER and what exactly is equipment derating? How does all of this affect your wallet when it comes time to pay your electricity bill? And what can Liquid SEER achieve for you? Let's dive in:


The ability of your machine to remove the heat or BTUs (British Thermal Units are the measurement of heat) from your home and exchange it with "conditioned" or cool air is defined by the BTU output of your equipment. Air conditioning units are sized according to tonnage per hour, and calculated per 12,000 BTUs removed per ton of conditioned air. So, a 3 ton unit can essentially remove 36,000 BTUs from your home per hour. The amount of electricity consumed during this process is calculated and equipment is given an efficiency rating based on how much electricity is consumed in the process of heat removal.


The overall efficiency rating of air conditioning equipment is referred to as EER. EER stands for Energy Efficiency Ratio, and this measures equipment cooling capacity and power consumption. The higher your machine's EER rating, the more efficiently it is supposed to run, and this lowers your electricity costs. This rating is usually calculated at an outdoor (ambient) temperature of 95 degrees F and an inside (return air) temperature of 80 degrees F with relative humidity at 50%. If your machine operates in conditions outside of these parameters the efficiency will vary. The more intense the working conditions, i.e. higher ambient temperatures, return air temperatures or increases in humidity the more your equipment will struggle to perform and its efficiency will decrease.


Equipment SEER rating measures efficiency of a cooling system. SEER stands for Seasonal Energy Efficiency Ratio. This rating is determined by measuring a machine's cooling output in relation to the electricity it consumes over a specific period; a season. Think of SEER rating as a snapshot of the maximum efficiency of how a unit could perform during a given season under certain conditions. The higher a machine is rated the more efficient the unit is considered by manufacturers to be. But this can be deceiving to consumers for a number of reasons, not the least of which is derating, which we'll get to below.

HVAC.COM has information about the costs of higher SEER units versus the benefits in terms of energy/money savings.

The most important thing to understand about EER and SEER ratings is that equipment performance is not fixed. A machine may receive an EER/SEER rating but a key point to remember is that those ratings are based on a set of specific operating conditions. If the operating conditions of your equipment varies from the rating parameters then your equipment's performance will vary, too. When conditions are such that equipment performs less efficiently than the EER/SEER rating it is called equipment derating.


You'll hear retailers touting higher SEER/EER units as being the best, telling you that by investing in a more expensive machine you'll reap the rewards in energy savings. What they don't often talk about is equipment derating. In fact, consumers are generally unaware that their expensive high SEER/EER equipment was rated to operate within defined conditions and that when those conditions fluctuate, so does the BTU output of their equipment and this changes the operating efficiency.

Once the ambient temperature and/or humidity rises above a defined limit the efficiency of the unit begins to decrease. The output capability of that unit decreases linearly in correlation with the increase in ambient temperature and humidity. What does that mean to you as a homeowner? Well, your 18 SEER unit won't perform at the energy efficiency of an 18 SEER unit when outdoor temps rise above 95 degrees and/or 50% humidity. It's the reason many homeowners wonder if their air conditioning equipment has failed during a heat wave or they complain that their home feels muggy.

Often, in order to achieve higher EER/SEER ratings, manufacturers will push the design of their equipment by using smaller smaller components which will draw less energy, but when working inside of stressful environmental conditions, those smaller components can't handle the heat load being placed upon them and all their beautiful energy efficiency begins to breakdown.

Liquid SEER

We talk often about Liquid SEER shifting the paradigm within the HVAC industry. Why? Because we've blown the ceiling off of efficiency ratings. By increasing the thermal capacity of equipment, Liquid SEER increases a machine's output of BTUs. Think back to removing heat in your home and replacing it every hour with one ton of air that's been cooled. Liquid SEER helps your machine cool more air per hour using less energy. Liquid SEER works on improving energy efficiency from two angles of the air conditioning process: it makes your equipment more powerful at BTU output and it helps equipment consume less electricity during that same process.

What would the benefits of Liquid SEER look like for a homeowner? Using the example from HVAC.COM  the average cost of a 3-ton, 15-SEER AC is $5,750, while a 3-ton, 20-SEER system costs about $8,300. With the 20-SEER unit, you will only save $11 a month on electricity costs, meaning it would take more than 19 years to break even.

But what if you could turn your less expensive 15 SEER unit into a more efficient machine with Liquid SEER?

Compare our case study 4-ton Carrier 50TVA4831TP 14 SEER package heat pump in cooling. You can see derating in action with this case. Notice the temperatures that the machine was operating in: 110°F outdoor temp/57°F wet bulb 37,950 BTUs sensible at 4.5 kWh. Notice the air conditioner is rated 14 SEER, yet because the operating conditions caused derating it was operating at 8.4 SEER.

After an application of Liquid SEER the equipment was operating in similar conditions: 110°F outdoor/56.3°F wet bulb, the unit produced 48,240 BTUs, (sensible BTUs: 48,038; latent 201) at 4.1 kWh. The Improved Liquid SEER performance was 12 SEER. Liquid SEER helped the equipment regain its capacity for BTU removal and reduced the wattage the unit was using to create the BTU removal.

And what would that look like for energy savings? Let's say outdoor temps stayed above 95°F for the month. Assuming the .4 kWh savings per hour reflected after Liquid SEER and that the air conditioner runs 12 hrs/day over the course of 30 days at .13 cents per kWh that would result in $21.60 in savings per month.

Back to the HVAC.COM example which says that with the 20-SEER unit you will only save $11 a month on electricity costs... but did they calculate derating into that number? Because under the example operating conditions above, a 20 SEER unit would also derate.

With Liquid SEER you can truly get more out of your equipment using less energy. Good for your wallet and the planet. Liquid SEER is the black coating that delivers big green benefits.


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