SEER stands for Seasonal Energy Efficiency Ratio. It is a measurement of efficiency for HVAC units. It is mostly used for units under 5 Tons.
Before we dive into how to calculate SEER there are two things you should understand. What is efficiency? and What is EER?
Check out our other article to understand efficiency better.
EER stands for Energy Efficiency Ratio. Like SEER, both are used specifically for HVAC units. EER is a measurement of efficiency but is a bit simpler than SEER.
EER = Output Cooling Energy (BTU) / Input Electrical Energy (Wh)
To keep EER consistent between units we use a standard set of ambient conditions. An outside temperature of 95°F, indoor temperature of 80°F with 50% humidity, and at 100% capacity.
The output cooling energy is measured in BTUs. The input electrical energy is measured Wh. The amount of Wh required to produce the needed BTUs determines the unit’s Energy Efficiency Ratio.
This leads us to SEER.
Seasonal Energy Efficiency Ratio measures the unit's efficiency over the entire cooling season. In other words, it uses varying outside and indoor air temperatures. Because it is not measured during one set of temperatures, it makes it a little harder to determine.
But, when a unit is actually installed it will experience varying temperatures. SEER gives the user a better idea of what the efficiency will actually be.
SEER is typically higher than EER. The efficiency of a unit is typically higher when the outside air is cooler because it doesn’t have to work as hard. This higher efficiency during the colder days increases the overall efficiency.
SEER = Seasonal Output Cooling Energy (BTU) / Seasonal Electrical Energy (Wh)
IMPORTANT: When you are comparing the efficiencies of units, make sure you are comparing apples to apples. Compare values of EER to EER or SEER to SEER. You cannot compare an EER value of one unit to the SEER value to another. These values are different, and by comparing EER to SEER you will get an incorrect impression. Like apples to oranges or broccoli to chocolate, it just doesn't work.
On the back of your air conditioner look for a yellow and black sticker that says "EnergyGuide".
This sticker will tell you the SEER rating and other efficiency data. Depending on the type of HVAC unit you have, here is where you can find the sticker:
If you have a split system, it is usually on the back or side of the condensing unit. A split system will have two components, one outside and one inside on the wall, in a closet, or in your attic.
The outside unit is called the condensing unit. It is typically located outside on the ground or possibly on your roof. It looks something like this:
Or like this:
If you have a packaged unit, your HVAC system is consolidated into one unit. Your system is located either on your roof or in your attic. The Energy Guide sticker is either conveniently located on the outside or you may have to open the side panel to find it on the inside.
WARNING: Make sure your unit is off before opening any panels. A unit in operation may have turning motors that you can get caught on.
For older units, where the sticker may not have existed or the sticker may not be legible anymore, you are not out of luck. You can find the efficiency in the manual or possibly on the data plate.
If your AC tech wasn't so generous you have one last shot. Find the model and serial number which you can use to search for your manual or call the manufacturer.
Because manufacturers are always looking for an opportunity to sell to you they are usually very nice in providing any information you need on the units.
To calculate EER we only need two values: BTUs and Wh (watt-hours). You can find both of these numbers on the unit or in the owner's manual.
EER = Output Cooling Energy (BTU) / Input Electrical Energy (Wh)
In the numerator you have the cooling capacity in BTU, this can also be known as the “tonnage” of your unit. If you know the Tons just multiply that by 12,000, that answer is equal to your cooling BTUs.
Cooling Capacity (BTU) = Tons x 12,000
OR
Cooling Capacity (Tons) = BTU/12,000
Next, divide by the electrical energy in Wh. The result is your EER value, or efficiency.
If you are looking to convert this to SEER, it gets a little complicated. Just understand, that the difference between EER and SEER is the “S”, Seasonal. It is an efficiency that is achieved through measuring the efficiency during different scenarios. No equation will be 100% accurate. However, there are a few that come pretty close, just make sure you use the right one.
For EER values less than 14:
This first formula is a good rule of thumb option but not very accurate, divide EER by 0.875:
SEER = EER/0.875
This second formula provides a little more accuracy but is more involved:
SEER = (1.12-√(1.2544-0.08*EER)) / 0.04
These will probably be enough for what you are looking for. For values of EER that are greater than 14, these equations will be less accurate so walk with caution.
