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Use the Energy-Efficiency Rating to Buy the Best AC for Your Home

If you’re looking to upgrade your HVAC system, one of the most important factors to consider is an HVAC unit’s energy-efficiency rating. This is true for all types of heating and cooling equipment, whether it’s a furnace, air-source heat pump, or AC unit. Not only are energy-efficient units better for the environment, but they’re also better for your wallet too. Buying a unit with a high energy-efficiency rating will translate to more cost savings on your home utility bills.


But what is considered a good rating and what do you need to know before upgrading your unit? Entek specializes in helping homeowners find, install, and maintain energy-efficient heating and cooling equipment. Here’s how you can use energy-efficiency ratings to find the right AC for your home.

An AC’s energy-efficiency rating is based on the unit’s cooling capacity and the amount of electricity it requires to operate. There are three types of energy-efficiency ratings for AC units:

  • Energy Efficiency Ratio (EER)
  • Combined Energy Efficiency Ratio (CEER)
  • Seasonal Energy Efficiency Ratio (SEER)

Portable AC units use the EER, window units use the CEER, and central AC units use the SEER.


For portable air conditioners, the cooling capacity is measured in BTUs (British thermal units) per hour, and the power input is measured in watts. The ratio of BTUs to watts is what determines the EER. If you’re buying a portable AC unit, you should look for an EER of 10 or higher. In fact, the higher the rating, the better.

But to choose the most energy-efficient portable air conditioner unit, you have to look at more than just the EER rating. You should also pay close attention to the BTU. After all, sizing is key when it comes to selecting the right heating and cooling equipment. A properly sized AC unit will cool a room much more efficiently than an improperly sized one.

To know what BTU to look for in a portable AC unit, you will need to measure the square footage of the room where your unit will be located. Once you have the square footage, you can use this ENERGY STAR guide to figure out the cooling capacity (BTU) your unit should have. Once you locate a unit that has the cooling capacity you need, look for the amount of wattage it uses. You can divide the BTU by the wattage to get the EER. For instance, if a unit has a BTU of 12,000 and uses 1,200 watts, the EER will be 10.

If you can’t find the EER displayed on a unit, check for the BTU and watts under product specifications. You can use the formula discussed (BTU per hour divided by watts) for calculating the EER.


Similar to the EER, the CEER will help you determine the energy efficiency of a window AC. The key difference, though, is that this ratio measures the energy efficiency of a unit when it’s operating as well as when it’s in standby mode. Using both of those values, you get the combined energy-efficiency ratio, or CEER. As with the EER, the higher the number, the more energy-efficient the unit will be.


Unlike the EER and CEER, which measure a unit’s immediate energy efficiency, the SEER measures the energy efficiency of an AC for the entire season. No surprises here … the higher the SEER, the more energy-efficient the unit will be. HVAC units, or central ACs, will typically use SEER ratings.

To calculate the SEER, you’ll begin the same way you did when computing the EER. You’ll find the BTU of the unit and the number of watts it uses. But here’s where things differ a little. You’ll need the total number of BTU and watts used throughout the season, rather than per hour. So you’ll have to do some additional calculations.

Let’s say you’re away from home for part of the day and don’t run your AC 24/7. We’ll say that the typical amount of usage for an AC unit is about eight hours per day. You’re most likely to use your AC unit in the late spring and throughout the summer, probably for about 125 days total. If you believe you use your AC unit more than that, add on some extra days.

Now, you’ll multiply 8 by 125 for a total of 1,000 hours. Multiply the BTU and the number of watts by 1,000. Next, divide the total number of BTU by the number of watts to get the SEER rating.

According to the Department of Energy, if you have an older unit with a SEER of 9 and you upgrade to a unit with a SEER of 14, you’ll reduce your energy usage by more than 35 percent. That means if your monthly utility bill is around $100 a month, an upgrade could reduce your monthly bill to $65 or less.


If you’re having a hard time locating a unit’s energy-efficiency rating or simply don’t want to have to crunch the numbers yourself, there is a quick and easy way for you to determine whether a unit is energy efficient. Simply look for the ENERGY STAR label.

For a system to have the ENERGY STAR label, it must meet performance requirements set by the US Environmental Protection Agency. Units with the ENERGY STAR label are highly efficient units with EER and SEER ratings that are greater than other new models on the market. You can use this tool to see how much money you could save by upgrading to an AC unit that has the ENERGY STAR label.

If you need assistance properly sizing your unit or selecting the model that’s right for you, the team at Entek can help. Of course, finding an energy-efficient AC unit is just one step to making sure your home performs at its best. Take advantage of our home performance test to find out what other energy-efficient upgrades could benefit you.

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