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Uniform Energy Factor Explained

Note: This post may contain affiliate links. This means that at no cost to you, we may receive a small commission for made purchases.

High energy consumption is one of the significant concerns people have while purchasing an electric water heater.

Many people are afraid whether their electricity bill will skyrocket once they get used to an electric water heater system at home. Part of it is true that both tankless and tank-type water heaters need a high amount of electric energy to function ideally.

Still, you can get over this problem by choosing a water heater that goes along with your requirements. And Uniform Energy Factor, better known as UEF, is an effective way to know the energy efficiency and consumption estimates of a water heater.

Still, many of us lack the basics of the Uniform Energy Factor. Of course, it can be a problem while picking the best water heater for your needs.

This is a brief guide to what is Uniform Energy Factor and how it can help you understand the energy-savings aspects of your water heater. We will start with the basics, of course.

What Is Uniform Energy Factor?

table with uef values

Uniform Energy Factor, better known as UEF, is a metric developed by the Department of Energy, the United States of India.

The metric is designed to let the user see the energy efficiency of water heaters. Each water heater model will have a unique UEF rating, indicating the energy efficiency while heating water.

In the past, Energy Factor (EF) was used to identify the energy savings aspect, but UEF has improved in quite a few ways.

Nowadays, UEF is considered the standard for understanding whether a water heater is efficient enough in terms of power consumption. However, a UEF rating is not universal.

You cannot use the Uniform Energy Factor to compare any given water heaters. Instead, you can use UEF to compare two water heaters within the identical BIN. As you may already know, there are four BINs in the industry:

  • Very Small: This bin contains tank-type water heaters with a first-hour rating of fewer than 18 gallons or tankless water heaters with a max GPM of less than 1.7
  • Low: This bin contains tank-type water heaters with a first-hour rating between 18 to 51 gallons and tankless water heaters with a max GPM between 1.7 to 2.8
  • Medium: In this bin, you can find tank-type water heaters with a first-hour rating of 51 to 75 gallons and tankless water heaters with a max GPM of 2.8 to 4.
  • High: This is the highest bin, and you can find tank-based water heaters with a first-hour rating of 75+ gallons. On the other hand, tankless water heaters in this category must have a max GPM of 4+.

For example, you can take two water heaters that belong to the medium bin and refer to their UEF rating to understand which one is more energy-efficient.

However, you cannot use the method if you take one water heater from the High bin and another one from the Low bin.

So, these are the basics you should know about Uniform Energy Factor as such.

How Does It Affect Me?

benefits of UEF

You might have figured this out already, but we will explain things a bit further. When you want to choose between hundreds and thousands of water heaters from the market, UEF ratings are a great way to filter products.

You cannot compare and contrast the numbers of all the products in one category. Even when you narrow it down to a specific type — for example, tankless water heaters from the High bin —, selection is a little tricky.

At this point, you can look at the UEF to understand which water heater is better when you want to save as much as possible on an electricity bill. Even when you have time to compare the numbers of specific models, the results may not be that accurate.

However, since the UEF is a metric designed and proposed by the Department of Energy, the ratings tend to be more authentic. Therefore, you can look at the UEF ratings if you need a more accurate look at things.

In short, your understanding of the UEF ratings will help you choose the better water heater for you. It must also be clear to you that the UEF ratings impact many performance factors.

Performance Factors Impacted By UEF

As we said earlier, the UEF rating of a water heater is a result of many pointers. So, if you see water heaters with two different UEF ratings, keep in mind that you will feel some difference in the following factors.

These factors have a direct relationship with what is called the performance of the water heater. Regardless of the type of water heater you have, you may have to wait longer for hot water if you have a low-performance heater.

First Hour Rating

what is first hour rating

First Hour Rating or First Hour Delivery is one of the essential factors impacted by UEF. It refers to the amount of hot water a water heater can generate in the first hour.

Because of the current metric in use, we can now have an accurate idea about this. Of course, a water heater with a better first-hour rating will have better performance, meaning that you would not have to wait for long.


Capacity refers to the amount of hot water a water heater can store for instant consumption. Depending on the amount of money you can pay, you can find water heaters with different capacities.

As you can guess, a water heater with a high-capacity tank would need more electric power to heat everything when compared to a water heater with a low-capacity tank.

Estimated Energy Cost Savings

As you may know, water heater manufacturers mention the amount of money you can save by choosing one water heater over another model.

As you can guess, the UEF rating will play an essential role in determining this figure. If the water heater model has a high UEF rating, the estimated energy cost savings will also be increased. There could be some impact on the heating performance of the water heater model as well.

While these three factors remain the most important ones, you can find other ones as well. For instance, if you have a tankless water heater, the maximum GPM of the device will be impacted by the UEF rating. Similarly, you can find some connections between the temperature coverage, water pressure, and recovery time with the UEF rating.

In short, when you go for a water heater with a high Uniform Energy Factor rating, you must be aware of the factors we have mentioned above. If you are not, the water heater may not keep up with your needs.


how is uef calculated

As we mentioned in the introduction, the Department of Justice used Energy Factor ratings before the Uniform Energy Factor ratings came into effect. Of course, this transition happened due to a few problems in the EF rating systems.

The change occurred in June 2017. So, if you have purchased a residential water heater after the date, it should have a UEF rating instead of an EF rating. It needs to be noted that commercial water heaters do not come under the purview of UEF ratings.

Here is a quick comparison between EF and UEF.

  • EUF presents a more accurate idea about the first-hour rating and first-hour water heater delivery compared to EF. It means a UEF rating will be a better way to understand how much hot water you can get in the first hour.
  • In EF rating, the manufacturer could have hidden the actual capacity of the water heater tank using the gallon grouping technique. For instance, if a water heater had an actual capacity of 37 gallons, a manufacturer could have rounded off the figure to 40 gallons. With UEF, the DOE has made it tough to do. Even though a manufacturer can advertise using the rounded-off figure, it has to disclose the actual storage capacity on the specifications page. More importantly, because the rating is based on a more accurate figure, your estimates would also be closer to real life.
  • Once again, you can have a better understanding of the money you can save annually. It is partly due to the use of accurate figures, such as capacity and first-hour delivery. But, the general idea that the DOE now demands better transparency when talking about water heater specifications also plays an essential role.

We should also keep in mind that the products shipped with an EF rating must be converted to a UEF rating. Most manufacturers offer a platform where you can input the EF rating of a specific model and know the UEF rating in a few seconds.

How Is UEF Rating Calculated?

Switch off an electric boiler.

As you have seen, UEF rating is an essential thing in water heaters, regardless of the type of energy they use. Tankless, tank-type, and hybrid water heaters would also have this rating as long as they are made for residential use.

On the other hand, you have to look at different things to understand the energy efficiency of a commercial water heater.

Now, we will look at how the Department of Energy has designed the procedure of UEF rating. Before that, you have to keep in mind that the DOE requires the water heater to meet some more conditions.

The heater must be using single-phase electricity only. Second, the maximum water temperature from the heater must be capped at 180F. Third, the device must conform to the limitations set regarding storage volume.

We do not want to get into the technicalities of the process. However, there are a few phases before a brand can get a UEF rating for one of the products. In the first phase, the water heater would be tested for its tank capacity, first-hour delivery, and max GPM while in use.

Based on these results, the device would be put into one of the four bins. We have talked about the bins in the introduction in case you want to know.

In the second phase, the whole process of comparison and rating will take place. We must note that EF test methods did not pay much attention to the draw patterns of different models. It was one of the reasons why the EF ratings were quite unreliable at times.

However, because UEF ratings are based on draw patterns and apply to water heaters from the specific category, everything is more transparent.

Depending on the type of water heater you have, the DOE has also recommended the minimum UEF rating. However, as a general rule of thumb, you should choose a water heater with a better UEF rating.

You may have to spend a higher amount to make it possible, but you can earn back the money within a few years or over ten years.

How Much Am I Saving?

how much could you save

We cannot give you a specific answer without checking the specifications of the model. If you are getting the water heater from a trusted source, however, you can count on the promises made by the manufacturer.

If the estimated savings go in sync with the UEF rating of the product, you can stay confident that you will be able to save a good amount by the end of the year.

Nevertheless, you can see the difference when you upgrade from a water heater with a low UEF rating to one with a high UEF rating.

Even though the changes would not be visible from day one, you will notice the healthy trends over a few months. We must also keep in mind that a water heater with a high UEF rating is beneficial to the environment to a great extent.

The fact that you can have hot water without exhausting energy sources as much as you used to is often an overlooked one.


We believe we have cleared all your doubts regarding Uniform Energy Factor and how it helps you choose a suitable water heater for your residential needs.

We have tried to explain everything without getting into the technical aspects, and we believe it will help all water heater buyers out there.

author avatar
Charlie Hardcastle


On Key

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