How Long Will Hot Water Heater Stay Hot Without Power

An unscheduled power outage can be frustrating for a number of reasons. No TV, no microwave, no lights! But what about hot water? Will a power outage take away your hot water as well? In this article, we have the answers you need. We’ll break it down based on the type of water heater you have to let you know how long you can expect your hot water to last during an outage.

A water heater

How Long Will Water Stay Hot in Water Heater Without Power?

First of all, not every water heater needs electricity to heat. Certain gas water heaters do not require electricity to run, and you won’t lose your hot water during a power outage. Additionally, it depends whether you have a tanked or tank-less water heater.

Of course, a tank-less option won’t store water, so it won’t provide hot water during an outage. If your water heater has a tank, it will depend on the tank capacity, the outside temperature, the level of insulation, and more.

Generally speaking, a 40-gallon tank will provide you with about 30-40 minutes of hot water before running out. The bigger the tank, the longer it will last.

As you can see, that’s a lot to consider. Next up, we’ll dive into greater detail about which water heaters will work during a power outage and examine the factors that influence the longevity of your hot water supply.

Will My Hot Water Heater Work Without Electricity?

Unfortunately, this question has a different answer depending on your type of water heater. For this reason, we’re breaking it down based on the major types of water heater. We’ll examine how long you can expect your hot water supply to last with each option, and whether you will even lose your hot water at all:

Gas Conventional Water Heater

First up is the gas conventional water heater. This is the only water heater that might still work when there is a power outage. The determining factor is whether the water heater uses a pilot light to ignite the gas. Because these heaters rely on gas to heat the tank, they don’t require electricity to work, and you’ll still have hot water during a power outage.

That being said, this isn’t true of all gas conventional heaters. These heaters occasionally make use of electricity. You’ll have to check your specific model to know for sure.

Water heating rods

Electric Conventional Water Heater

Of course, because electric conventional water heaters rely on electricity, they won’t work during a power outage.

Related: Rheem Water Heater – Ultimate Trouble Shooting Guide

That being said, because these water heaters have a tank to hold the hot water, you can typically still get hot water during a power outage, depending on whether the tank was full of hot water at the time of the outage. However, as you use the hot water, it will be replaced by cold water. Therefore, the longevity of your hot water supply depends on the following factors:

  • The level of insulation on the water heater. Some people add an extra layer of insulation over the heater to prolong its use.
  • The size of the tank.
  • The exterior temperature, as it acts to cool down the water.
  • The temperature of the hot water when the power cut out.

Generally speaking, with more of any of these factors, the longer you can expect your hot water to last during an outage.

Related: How to get Hot Water Faster from a Tankless Water Heater.

Gas Tankless Water Heater

A tankless water heater heats the water as it passes through the unit. Although this water heater utilizes gas, it also utilizes electricity. Unfortunately, it won’t work during an outage. Additionally, because there is no water tank to store the water, you also won’t have a stock of hot water to draw from! While these units do have their upsides, usage during a power outage is not one of them.

Electric Tankless Water Heater

As you can probably guess, you’re also out of luck with the electric tankless heater. And with no tank, there’s no water to draw from.

Related: Rinnai vs Rheem Tankless Water Heater: Which is better?

A large water heater


As you can see, unless you have a conventional gas water heater that operates with a pilot light, you’ll be out of luck for heating water during a power outage. That being said, if your water heater has a tank, you might have a sizeable amount to draw from.

Of course, this is a rather small consideration in the grand scheme of things. When it comes to purchasing a new water heater, you’ll need to consider much more than this specific factor, but it’s definitely useful information to know.


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

A 40-gallon unit is one of the most common water heater tank sizes. The length that this tank will last during a power outage will be determined by the exterior temperature, the insulation on the tank, and the temperature of the hot water.

That being said, you can expect a 40-gallon tank to provide about 30-40 minutes of hot water (depending on the appliances you are using). Once the hot water is used up, it takes a 40-gallon tank about two hours to recover its hot water (assuming the power is turned back on).

Does turning up water heater make hot water last longer?

Yes, technically this would work, although it isn’t necessarily an efficient solution. Of course, by heating up your water to a higher temperature, it will take longer to cool down when the water heater is turned off (either intentionally or due to power outage). That being said, it’s not going to make a massive difference. It will slightly lengthen the time the water takes to cool, but it will also cost you more to heat up the tank!

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