How to Understand Water Heater Efficiency Ratings

What do the various water heater efficiency ratings really mean? We explain. Read about ENERGY STAR, energy factors, solar energy factors, and GPM.

Water Heater Efficiency Ratings: What to Know When Buying

When researching water heaters, you are bound to come across water heater efficiency ratings. Comprehending exactly what these ratings mean is imperative for finding the right water heater for you. Let’s dive deeper into this topic so that you will be well-informed and have a better understanding of exactly what factors affect a water heater’s efficiency rating.

What is the History of ENERGY STAR?

Back in the early 1990s, the United States’ government passed the Clean Air Act in an attempt to help raise awareness to the negative effects people have on the planet and to look for ways to minimize those effects. Soon after that act was passed, the United States Environmental Protection Agency launched the ENERGY STAR program.

Through this program, the government was able to set standards for various products, based on their efficiency ratings. The hope is that this initiative will help reduce the greenhouse gas emissions produced by Americans. So, when you purchase a water heater with an ENERGY STAR label, you know you are buying a product that has minimal impact on the environment. Way to go!

What Water Heater Efficiency Acronyms You Need to Know

Below is a list of acronyms you may come across while researching water heater efficiency ratings. These terms will also help you decipher the ENERGY STAR Criteria section of this article.

FHR (First Hour Rating)

This means precisely what you would expect it to. The FHR is an accurate prediction of how many gallons of water your water heater can produce in sixty minutes. The outlet temperature range your water heater would need to reach and maintain for this rating is 125°F to 135°F.

EF (Energy Factor)

This is the original measure of water heater efficiency. The Department of Energy developed this rating to help consumers find water heaters that use minimal amounts of energy. When it comes to scoring, the higher the EF number the better.

SEF (Solar Energy Factor)

Calculating the Solar Energy Factor is easy. Simply take the energy used by the solar water heater and divide it by the electrical energy used to make the system run. The same calculation can be done if you are running your solar water heater by gas energy instead of electric.

GPM (Gallons per Minute)

This refers to how much hot water a tankless water heater can supply in sixty seconds. It is measured in gallons of water and the temperature must reach over 77°F.


We have provided a list of some of the requirements a water heater would have to have in order to be labeled as ENERGY STAR. There are different specifications for each type of water heater. Please refer to the Acronyms You Need to Know Section if you have any questions.

Electric Storage Water Heaters

  • EF of 2.0 or higher for tanks that hold 55 gallons of water or less
  • EF of 2.2 or higher for tanks that hold more than 55 gallons of water
  • FHR of 50 gallons of water or more per hour
  • 6 year+ warranty

Gas Storage Water Heaters

  • EF of .67 or higher for tanks that hold 55 gallons of water or less
  • EF of .77 or higher for tanks that hold more than 55 gallons of water
  • FHR of 67 gallons of water or more per hour
  • 6 year+ warranty

Solar Water Heaters

  • SEF of 1.8 for electric energy supply
  • SEF of 1.2 for gas energy supply
  • 6 year+ warranty

Tankless Water Heaters

  • GPM of 2.5 or higher
  • 10 year+ warranty

What are the Financial Benefits of Energy-Efficient Water Heaters?

One of the most appealing aspects of finding a water heater that is labeled as ENERGY STAR is the financial ones. Because these water heaters are using less energy than their non-ENERGY STAR competitors, you will be saving money on your gas or electric bill. According to the ENERGY STAR website, homeowners save up to $3,500 over the course of the water heater’s lifetime. Now, that is something worth celebrating!

What You Really Need To Know About water heater efficiency

We hope you now have a better grasp on why water heater efficiency ratings were developed, what they mean to consumers, and how they will affect you personally. If you have any other questions or concerns regarding your water heater, please check out these other helpful articles.

Resources— ENERGYSTAR, Constellation