Is 40 Gallon Water Heater Enough? 

When buying a new water heater, one may ask – Is 40 gallon water heater enough for my family? Logical thinking will tell you to purchase a water heater with the biggest capacity possible.

However, choosing a water heater of the proper size is not as easy as it seems. There are many factors with a high likelihood of affecting the accessibility of hot water for each person in the house.

Factors as the size of your family and the type of water heater are just some of them. Keep reading to get well informed on this topic, as we discuss everything you need to know about 40-gallon water heaters.

How Many Gallons of Hot Water Does a Shower Use? 


When researching specific amounts of water a household needs, it’s always best to start from the average water usage.

Although it is unfortunately hard to answer this question, there are some general statistics out there.

A typical modern shower flows at a rate of 2 gallons per minute. However, it’s important to keep in mind that this includes both cold and hot water. [1]

This information doesn’t do much for us. The average person reading this is probably thinking of buying or replacing an existing water heater because of one common reason.

It’s because you’re not getting hot water from your water heater, or at least not enough for your family’s needs.

There are some stats out there showing a 20-minute shower uses about 50 gallons of hot water. [2]

However, an answer to a question of How many gallons of hot water does a shower use is very subjective.

Do you imply a shower lasting 10 or 20 minutes or more? How hot do you consider hot water to be?

The answer will depend on the lifestyle of every householder, and can therefore be hardly measured in averages.

This is why it’s important to research deciding factors for water usage. Let’s dive deeper into what those are.

Choosing The Proper Size of Water Heaters – Deciding Factors 


There are about 3 most important deciding factors that will greatly impact the size of water heaters your family will need. Those are:

  • Size of the family
  • First Hour Rating (FHR)
  • Type of the heater (gas/electric/other)

Let’s take a look at the roles of each of these factors.

Is 40 Gallon Water Heater Enough for a Family of 4? 


The size of the family is probably the most important factor you should take into account when discussing the heater’s gallon size.

This is because a family of 2 and a family of 4 won’t use up the same amount of water. This is also the case for the use of hot water, for that matter.

That being said, a 40 gallon water heater will be just enough for a family of 4 (in most cases).

However, keep in mind that it also won’t be enough in some other cases. For example, in a family of 4 adults.

In the family of 3 adults and one baby, a 40 gallon water heater is probably enough.

If you want to be sure and play it safe, purchase a 50-gallon water heater for the family of 4. Do this especially if you have 2 or more household members who take long and hot showers.

Here is a general estimated amount of water for the size of a family using it:

  • 30-gallon water heater – sufficient for the family of 2 (in some cases 3)
  • 40-gallon water heater – sufficient for the family of 3 (in some cases 4)
  • 50-gallon water heater – sufficient for the family of 4 (in some cases 5)
  • 60-gallon water heater -sufficient for the family of 5 (in some cases 6)
  • 70-gallon water heater – sufficient for the family of 6 (and so on)

That being said, every household situation is unique with their hot water usage.

It’s up to you to measure the approximate amount of hot water being used by your family members.

In order to do that, you’re going to need some guidelines – which leads us to the next step.

First Hour Rating (FHR) 

FHR or First Hour Rating indicates how many gallons of hot water a water heater can generate in an hour. In other words, an FHR shows the amount of hot water your water heater can generate in the first hour. [3]

This indicator is very important to take into account when buying a new water heater or replacing the old one.

Particularly, it’s important because it will give you a pretty precise performance you can expect from a water heater.

When buying a new water heater, it should come with a first-hour rating label. However, you may want to calculate it yourself, so keep reading to calculate an FHR of a particular water heater.

The First Hour Rating is influenced by the maximum capacity and recovery rate of a water heater.

To calculate the first-hour rating, multiply the maximum capacity of a heater by 70% (0.70).

The 70% stands for the amount of hot water the heater can deliver in the peak hour. As you use the hot water, the cold water enters the tank, making the existing hot water a bit cooler.

Then, add the recovery rate of a heater to that result. A recovery rate indicates the amount of time needed for hot water in the tank to recover after it’s lost.

To put it simply, calculating the first-hour rating looks like this:

Tank’s max capacity (in gallons) X 0.70 + recovery rate = first-hour rating

To use an example, it looks like this:

40 gallons X 0.70 + 40 GPH = 68 GPH first-hour rating

This is a very useful estimate, especially when you’re calculating the amount for the water heater you’re planning to buy. In this exact case, it shows us that you’ll get 68 gallons of hot water in the first hour of usage.

Gas or Electric Water Heaters?


Understanding the energy usage of water heaters is also important when choosing the gallon size.

The water heaters take up about 20% of each home’s utility bill. [4]

Choosing between electric vs. gas water heaters is not a hard task, but it still shouldn’t be taken lightly.

Is 40 gallon water heater enough for a gas or electric tank?

Does it make any difference to energy usage?

What it really boils down to is the fuel source your home already has. If your home uses only electricity and has no access to natural gas, then you’ll choose the electric heater and vice versa.

This might be the case for you as one in four US homes is all-electric. [5]

Moreover, there are certainly some differences between electric and gas water heaters. Both are, however, measured by input – the spent gas/electricity per hour to heat the water.

While input in electric water heaters is measured in watts, the input in gas heaters is measured in BTU’s (British Thermal Units).

Electric water heaters use electric resistance coils to heat the water. On the other hand, gas heaters use heat from burning fuel to heat water.

While gas water heaters cost less to operate, electric heaters are typically more energy-efficient and easier to install.

We recommend you take PROS & CONS into account when deciding between the types of heaters.

What’s even more important is to adjust this choice to the power source you already have in your home.

The same goes for tankless water heaters, which can be powered either by gas or electricity.

Lastly, keep in mind there are more things to consider with how a heater works, other than its gallon size. Read on about condensing vs non-condensing ones, for example.

The Takeaway

Hopefully, now you know that the answer to the question – Is 40 gallon water heater enough – is quite subjective.

Whether or not a 40-gallon water heater is enough for your family’s needs depends on a couple of factors.

Those are the size of the family, the first-hour rating, and the power source of your water heater.