How Long Should A 40-Gallon Water Heater Stay Hot?

When you are getting ready to install a new water heater or replace an existing tank, understanding the capacity is important. You need to ensure the heater you purchase will support everyone in your family. You might be wondering how long a 40-gallon water heater should stay hot. We did the research to bring you the answer.

Generally speaking, a 40-gallon water heater that is being used continuously should stay hot for approximately 45 minutes to an hour. However, this number will depend on several factors including your tank's insulation and whether it runs on gas or electricity. 

You now have a basic idea of how long a 40-gallon water heater should stay hot, but there is still a lot you don't know. Stick around to find out which factors affect this time, how long it takes for the water to heat back up, how much water a 20-minute shower uses, and much more.

40 gallon smart high efficiency water heater storage tank in the basement of a residential home, How Long Should A 40-Gallon Water Heater Stay Hot?

How Long Should a 40-Gallon Water Heater Stay Hot?

Storage water heaters keep hot water stored in a tank for immediate use. Once that water has been depleted, the water heater must refill and reheat the water.

In most cases, you will have approximately 45 minutes to an hour of continuous use before you run out of your hot water supply. However, this number depends on several factors, including the following:

  • Amount of hot water being used
  • Flow rate/water pressure
  • Tank insulation

Shower with flowing water and steam

Amount of Hot Water Being Used

The amount of hot water you are using at one time plays a major role in the length of time your water will remain hot. If you are running straight hot water, for example, you will run out much quicker.

However, if you turn the hot water on halfway and the cold water on halfway, you should be able to let it run for approximately 45 minutes to an hour.

Flow Rate/Water Pressure

Some homes have less water pressure than others. Likewise, certain shower heads make it possible to adjust the water stream. If you choose a setting that allows more water flow than normal, you will lose hot water faster.

By installing a low-flow showerhead, you can save 10 gallons for every 10 minutes you are in the shower.

Click here to see this low-flow showerhead on Amazon.

Tank Insulation

The length of time your water remains hot can fluctuate depending on how well your tank is insulated. If your tank is good at keeping the frigid air out, your water will not be as cold inside the water heater. This will lessen the amount of work your unit has to do to keep the water hot.

How Long Does it Take for a 40 Gallon Water Tank to Get Hot?

Boiler room - gas heating system

Once you run completely out of hot water, you will have to wait for your tank to refill and reheat. This time will vary depending on several factors. The most significant of these variables being whether the water tank runs on electricity or gas.

Gas water heaters are typically more efficient than electric units. Once all the hot water has been depleted, you can expect a gas water tank to supply you with additional hot water within roughly 30 to 90 minutes, whereas an electric water heater will typically take about 1 1/2 to 2 hours to reheat.

However, these times also depend on the outside temperature. During the summer, your water heater will reheat much quicker than it would during the winter.

Likewise, if you live in a climate that experiences severe cold, your water heater will not reheat as fast as a unit owned by a person living in the south.


According to Energy Saver, when purchasing a new water heater, you should always check the ratings first.

The numbers many homeowners are most interested in are the First Hour Delivery Rate and the Recovery Rate. For both of these, the higher the number, the better. However, it's helpful to know the EF rating as well.

Energy Factor (EF) Rate

Many newer water heaters are more energy efficient than older models. Therefore, when you purchase a new unit, it's a good idea to check its EF rating.

The EF rating is determined by factoring in the recovery time and the FHD. Specialists then use those numbers to calculate how much energy the heater uses compared to how much hot water it produces each day.

Recovery Rate

The recovery rate tells you two things. First, it specifies how many gallons of water the tank can provide per hour.

Second, it defines how soon after depletion the tank will be able to provide you with more hot water. For example, an acceptable recovery rate for a gas water heater would be about 40 gallons per hour or higher.

First Hour Delivery (FHD) Rate

The first hour delivery rate is very similar to the recovery rate. It specifies how much hot water the unit can provide in an hour's time. However, this number is dependent on there being water already in the tank. Recovery rate, on the other hand, refers to an empty tank.

How Long Should a 40-Gallon Water Heater Last?

40 gallon water heater storage tank in the basement of a residential home

For the most part, a 40-gallon water heater should last between 10 and 12 years. Some units come with a warranty, so you should check before buying. The following are a few signs that it may be time to replace your water heater:

  • You are getting less hot water than normal
  • Your water temperature varies severely
  • You notice a leak in your tank
  • Reduced flow in hot water
  • Foul odor or unusual color

If you notice any of these issues, do not try to service the unit yourself. Doing so could be dangerous. Instead, make sure you hire a licensed plumber. In fact, depending on the state in which you reside, it may be illegal to work on the water heater without a license.

Click here to view this 40-gallon water heater on Amazon.

Is a 40-Gallon Water Heater Enough?

The answer to this question will depend on how many people are in your home and how much hot water you use on a daily/hourly basis. 40 gallons is a fairly popular size for water heaters. Generally speaking, a 40-gallon tank will be enough to supply plenty of hot water for a family of 4.

How Many People Will a 40-Gallon Water Heater Serve?

Depending on how much hot water your family uses, a 40-gallon tank can typically serve 2 to 4 people. If you have more than 4 individuals in your home, you may want to consider upgrading to a 50-gallon tank.

Click here to view this 50 Gallon water heater on Amazon.

How Much Water Does a 20 Minute Shower Use?

Hand regulate the temperature of hot water in electric water heater

Although not every shower puts out the same amount of water, you can expect a 20 minute shower utilizing a standard-flow showerhead to use roughly 50 gallons of water.

However, if you have a low-flow showerhead, you will only use about 40 gallons during a 20 minute shower. This number increases greatly with a showerhead that provides extra waterflow.

Do You Need a Permit to Replace a Water Heater in California?

There are a number of codes and regulations that must be met when installing a water heater in California.

For this reason, you are required to apply for a permit before replacing an existing water heater. Although permits can cost anywhere from $40 to $400, it will ensure you do not unknowingly violate any of the various codes, which would cause you to pay hefty fines.

Do You Need a Permit to Replace a Water Heater in Florida?

Person hands using stamper on document with the text approved

Not all areas of Florida require a permit before replacing a water heater. If you live in one of the following counties, however, you will need to obtain a permit and get an inspection:

  • Broward
  • Dade
  • Palm Beach

Do You Need a Permit to Replace a Water Heater in New York?

In all areas of New York, you need a permit before replacing an existing water heater. In some locations, you must hire a licensed master plumber, a licensed mechanical contractor, or a licensed gas fitter to install the water heater.

However, some counties allow homeowners to do the installation themselves. This is where the permit comes into play. To obtain a permit, the water heater installation must pass an inspection by a licensed professional, ensuring it was installed properly.

Do You Need a Permit to Replace a Water Heater in Texas?

As of 2007, the entire state of Texas requires permits before replacing water heaters. Additionally, Texas does not allow homeowners to do their own water heater installations. Instead, residents must hire a licensed plumber to do the job.

In Closing

Water heaters often go unnoticed until there is a problem. We have become so accustomed to taking hot water for granted.

However, when we start losing hot water in the middle of a shower, we come to the quick realization that something must be wrong with the tank. If you are experiencing less than normal heating cycles, it may be time to replace your existing water heater.

For more information on water heaters, check out these other helpful tips on our blog:

How Often Does A Water Heater Run?

Do You Need A Permit To Replace A Water Heater?

Water Heater Temperature Sensor Failure—What To Do?

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