There are several HVAC metrics for energy efficiency.

In many cases, the *Energy-Efficiency Ratio* (**EER**) is specified on the specification sheets. However, one of the most basic heating/cooling metrics – Coefficient Of Performance (**COP**) – is not.

Fortunately, you can easily convert COP from EER (as well as EER from known COP) with these two converters:

## Convert EER To COP

Here is an EER to COP chart with some examples of COP values based on EER rating:

## Convert COP To EER

We’ve calculated a few examples for you. You can see them here in the COP to EER chart:

## Formula For EER And COP

Coefficient Of Performance (COP) is a key metric for energy-efficiency of heating and cooling devices. Based on the first law of thermodynamics, we can derive that COP is calculated using the following formula:

**COP = Q /W**

where Q is heat (provided to the system in the case of heaters and taken from the system in the case of cooling devices) and W is work (electricity).

Based on the definition of COP, we can deduce a formula for estimation of EER rating based on COP. We can calculate EER from COP with this formula:

**EER = 3.41 × COP**

It’s a fairly simple formula that connects COP with EER. This equation is especially useful when we want to determine the Coefficient Of Performance for HVAC devices that use EER as a primary energy-efficient metric.

Room air conditioners, for example, are the ones that can be compared based on the use of EER ratings. You can check EER ratings of the best portable AC units here and convert them to COP as an exercise.

The low EER rating devices (and hence COP) are battery-operated air conditioners.

Thank you for the article.

Can you explain why the calculation of COP x 3.41 = EER doesn’t work for models on this Energy Star list?

https://www.energystar.gov/products/energy_star_most_efficient_2020/geothermal_heat_pumps

For example, the first American Standard model on the list is 18.1 EER but 3.9 COP. The EER is 4.64 times COP.

I’d be very interested to know your thoughts. Thank you.

Hello Robert, that does seem odd. Maybe this is the reason: COP is calculated for max. and min. temperature, namely COP = Tmin/(Tmax-Tmin). If they use a non-standard Tmin and Tmax, that might cause an alternate relationship between COP and EER.