How long does it take for a 20 gallon electric water heater to heat up

There isn’t much that can ruin your day quite as quickly as an ice cold shower, and if you have the wrong water heater, this could become your new normal. If your current heater is dying on you, don’t let the stress of the situation rush you into making the wrong choice for your replacement.

Before you choose a water heater, make sure you consider how long it takes for your water heater of choice to heat up. If you want to run lots of hot water at the same time, you’ll need a more powerful system than if you just want to have a daily hot shower.

So, how long does it take a water heater to heat water once it reaches the appliance?  While there are many factors which can affect the time, the chart below shows how long each type of water heater takes to heat up on average.

Table of Contents

• 1 How Long It Takes A Water Heater to Heat Up For The First Time
• 2 How Long Does it Take for a Gas Water Heater to Heat Up?
• 3 How Long Does it Take an Electric Hot Water Heater to Heat Up?
• 4 How Long Does it Take a Tankless Gas Heater To Warm Up?
• 5 How Long Does it Take a Tankless Electric Heater To Warm Up?
• 6 Factors That Affect Heat Up Time

How Long It Takes A Water Heater to Heat Up For The First Time

Water Heater Type	Time Takes to Heat Up
Gas Tank	30-40 minutes
Gas Tankless	0 minutes *
Electric Tank	60-80 minutes
Electric Tankless	0 minutes *

*Tankless water heaters provide almost instantaneous heat if sized and installed properly.

Chart Source

How Long Does it Take for a Gas Water Heater to Heat Up?

Your average gas tank heater takes about 30 to 40 minutes to heat water once it enters the tank. This initial heat up occurs when new water from your plumbing supply is fed into the tank.

A more specific explanation of why this takes 30 minutes requires some math. The heater’s tank size is obviously a major factor, as more water will take longer to heat. The next major factor is the heater’s BTU (or British Thermal Unit) rating. Simply put, a BTU is the amount of heat required to raise one pound of water by one degree Fahrenheit. A heater with more BTUs can heat water faster.

For example, the average hot water heater tank is 40 gallons. There are approximately 8.3 pounds of water per gallon, so our example tank has about 330 lbs of water to heat.

40 Gallons x 8.3 lbs Per Gallon = 330 lbs of water

If the water is already 60 degrees and you want it to reach 120-degree hot water, a temperature rise of 60 degrees is needed.

To avoid getting into full-blown thermodynamics calculations, we can simplify and say that a 40,000 BTU system with a 40-gallon tank needs one half of one minute to heat each gallon, resulting in a half hour heat up time.

If you have a smaller tank or higher BTU rating, your hot water heater’s warm-up time will be shorter. If you have a larger tank or lower BTU rating, on the other hand, it will take longer to heat your tank.

If you want an efficient water heater which will heat up your water in the amount of time you desire (after it runs out of hot water) as well as store a good amount of hot water, these are the specifications you will need to keep in mind.

Also, keep in mind that this is the amount of time it takes for new cold water to be heated in your tank. When turning on the hot water for the first time after your tank has been storing hot water already, you should have hot water within just a few moments because tanks store pre-heated water.

This amount of time it takes to heat up new water comes into consideration when all the hot water in the tank is used up. That’s when the gas tank water heater will have to start heating new water again from the incoming groundwater temperature.

A gas tank water heater will take approximately 30 minutes to heat up new incoming water for the first time.

How Long Does it Take an Electric Hot Water Heater to Heat Up?

Electric tank water heaters typically require double the amount of time compared to their gas counterparts. Electric elements, while typically more economical, simply cannot compete with the high performance of gas-fired systems.  From the time new water enters, it would take about an hour for an electric water heater to warm the 40-gallon tank described above.

This is why homes with larger water demands usually decide to purchase a whole house gas tank water heater instead of an electric model. Electric models are excellent for smaller homes and smaller water demands.

An electric tank water heater takes 60-80 minutes compared to 30 minutes that a gas tank heater takes to heat water.

How Long Does it Take a Tankless Gas Heater To Warm Up?

Tankless water heaters warm up your water “on demand”, so the distance from your heater to the appliance being used is the only consideration which determines how long it will take to receive the hot water out of your faucet.

If the system is working properly, this should not be more than a few seconds with a normal sized home. With a large home, it may take a few more seconds to travel through the water pipes and reach appliances further away from the heater.

A tankless gas heater heats up water instantly so it should only take a few seconds before that hot water travels through your pipes into your fixture.

How Long Does it Take a Tankless Electric Heater To Warm Up?

Just like tankless gas water heaters, tankless electric water heaters only begin to warm up your water once an appliance demands it. In other words, the water is not warmed until you turn on the dishwasher or turn in the faucet.

In most cases, an electric tankless heater will provide hot water within moments, but they can take a tiny bit longer than gas systems, due to the power of gas heat.

A tankless electric heater heats up water instantly so it should also only take a few seconds before the hot water travels through your pipes into your fixture.

Factors That Affect Heat Up Time

In addition to the factors we’ve already explored, such as tank size and BTU rating, there are other circumstances that could dictate how long your water heater takes to warm up water for the first time.

• Incoming Temperature – For both tankless and tank-style water heaters, the temperature that the water starts at will help determine heat up time. Because tank heaters store water and keep them heated, the incoming temperature shouldn’t affect it so greatly. Tankless heaters, however, feed incoming water on demand just moments before it comes out of your faucet. This means that if the groundwater temperature is very low, the water may not get as warm as fast. Both types of heaters can be affected by extremely cold ambient temperatures in the room or area where they are stored.
• Settings– Although water heaters seem relatively simple when compared with other household mechanicals, they often have more to them. If your heater isn’t working, a professional may need to come to check out any settings or calibration that could be negatively impacting its performance.  
• Age / Maintenance Issues – Just like any other mechanical equipment, your heater’s age and condition could eventually affect its performance, including how long it takes to heat up.  A lack of general maintenance, particularly failing to clean up sediment that may be in the pipes could cause performance issues as well. Pipe sediment is more likely in areas with hard water.
• Distance from Appliance– Sometimes it’s easy for the end user to forget, but your hot water is traveling from the ground, through the heater, and pipes in your home before reaching the appliance you are using. The farther your appliance is from the heater, the longer it could take for the heated water to reach it. A savvy installer should account for this when setting up your system, so it should not be too much of an issue.
• Pipe Diameter– In addition to the length of piping, the width of your water pipes could affect how long it takes the water heater to heat up. A wider pipe is beneficial as it carries more water, but it will require more water to be heated before the pressure builds enough for it to push through the remaining pipe system.

In summary, there’s a heater perfect for everyone out there. Whether it’s a classic tank or tankless, think about your needs before selecting one.

Now that you know how long it takes both gas and electric water heaters to heat up, see our review of the best models on the market.

With great brands like Bosch, Rheem, and Takagi, you’re sure to find a match!

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