How Long Does It Take A Water Heater To Heat Up?

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Categories Water Heating
Find out how long it should take for each different kind of water heater.

Are you looking for a new water heater but want to know how to choose the best model for your needs? Are you frequently running out of hot water mid-shower and wonder what you can do about it? Let’s explore how long it really takes a water heater to heat up.

Water heaters play an important role in each household — without them, we wouldn’t have hot water for daily life. But they aren’t magic machines capable of delivering an endless flow, and how fast they heat up depends on many variables.


How Long Does It Take a Water Heater to Heat Up

When it comes to water heaters, there’s a huge variety of sizes, types, and fuel or power sources. All of these influence how long it takes the water heater to heat up.

Gas Water Heaters

A.O. Smith GCR-40 ProMax Plus High Efficiency Gas Water Heater, 40 gal
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Gas boilers are one of the most effective, traditional, ways of heating water in a household. Gas has for long been a favorite power-source.

One of the benefits is low energy bills. Instead of using electric elements, they heat the water using gas burners sitting at the bottom of the tank. So, their recovery time is significantly faster.

The average gas water heater doesn’t take long to heat a full tank, although this depends on the size. A 40-gallon tank will take between 30 and 40 minutes whereas an 80-gallon tank will take 60 to 70 minutes.


Electric Water Heaters

Rheem MR50245 Marathon Tall Electric Water Heater, 50-Gallon
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Electric water heaters are a little less efficient. These use electric heating elements sitting inside the tank — somewhat like a toaster or an oven.

Their recovery time is a bit longer than gas-fueled units. With a 40-gallon tank, you can expect hot water within 60 to 80 minutes. For an 80-gallon tank, you’ll have hot water in about two hours.


Solar Water Heaters

Solar water heaters are powered by none other than our great sun (1). But, since we can’t rely on him 24/7, they’re usually backed by a standard electric water heater. This, of course, means that they take about the same amount of time as an electric unit.

That said, there are solar units available that rely solely on solar power. If that’s the case, you can expect a long waiting time on cloudy days. And, perhaps no hot water at all on the gloomy, sunless days.

Heat Pump Water Heaters

Stiebel Eltron ACC300 Accelera 300 Electric Water Heater, 80 Gallon, WHITE
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Heat pump water heaters are often called “hybrids” since they’re modified electric water heaters. Instead of generating direct heat, they use the incoming electricity to move the heat around, thus increasing their efficiency (2).

Heat pump units are usually high-tech, giving you the option for several different energy-saving settings. This typically includes a hybrid and a high-demand mode. In hybrid mode, the unit uses less energy, but this does increase the heating time.

When in hybrid mode, the waiting time for hot water can be up to two hours, depending on the tank size. However, if you switch to high-demand, the electric part of the unit will kick in and decrease the waiting time to about 60 to 80 minutes.


Tankless Water Heaters

Stiebel Eltron 224199 240V, 1 Phase, 50/60 Hz, 24 kW Tempra 24 Plus Whole House Tankless Electric Water Heater, Advanced Flow Control
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If you’re looking for a water heater with little to no waiting time, a tankless is perfect. Tankless or on-demand water heaters, work as you need them. They don’t have a tank which means that the water enters upon demand receiving heat as it circulates (3).

However, there are different sizes available, and most are meant as a point-of-use unit. With that said, the average waiting time is less than a minute.


Factors That Influence Heating Time

The expected waiting time is only a general estimation. Water heaters are affected by various factors that can influence how long they take to heat up. Some are universal across the different types, where others are more specific.

1. First Hour Rating

The first hour rating tells you the number of gallons the water heater can deliver within the first hour. It indicates the ability of the water heater after it has recovered a full tank to the desired temperature (4).

A high first hour rating means a shorter waiting time. The calculated number depends on fuel source, tank capacity, and the size of the heating elements or burners (5).

2. Size of Water Heater

The size of your water heater is another factor that can slow down the heating time. As you saw in our earlier examples, a larger tank size takes longer to heat up. This is simply because there’s more water to heat.

Larger tanks will generally have two heating elements or a large burner to speed up the heating time. Still, a smaller tank will heat up quicker.

With that said, the smaller tank will likely run out faster than the larger tanks. So although you’ll have hot water in less time, you’ll likely run out after minor tasks.

3. Inlet Water Temperature

The inlet water temperature, or temperature rise, is another factor that can seriously influence the recovery time. Depending on where you live, the inlet water will have different temperatures. It’s generally colder up North than what it is in the South.

When we say “temperature rise,” we refer to the temperature contrast between the incoming water and the preset temperature on the boiler. The colder the inlet water, the longer it takes to heat up.

4. Fuel Type

As you saw in our earlier examples, fuel type makes a big difference in recovery time. Gas water heaters are a lot faster when it comes to heating water than their electric cousins. This is because gas burners reach a much higher temperature than the electric heating elements.

Why Is It Suddenly Taking Longer?

Over time, your water heater will likely take longer to heat up. But if it happens prematurely, check the following:

1. Sediment Buildup

The most likely reason that your water heater is suddenly taking longer to heat up is sediment buildup. This is a common issue occurring over time as your unit ages. But if you have hard inlet water or neglect maintenance, it might happen a little earlier.

Sediment buildup is when the minerals present in the water begins to settle on the inside of the tank. It can occur even with soft water that’s low in minerals, but this will usually take a little longer before becoming noticeable.

Sediment buildup consists of dissolved minerals such as magnesium and calcium. These sit on the walls of the tank and the heating elements where they can seriously restrict the tank’s ability to heat water.

There are three main signs of a buildup:

  • The unit takes longer to heat up and you’ll run out a lot quicker than before.
  • The unit is making strange noises such as popping, knocking, or hissing.
  • Significantly higher energy bills.

The best way to fix this issue is by flushing the tank regularly. But if you have an electric unit, and the heating elements are damaged beyond repair, you must replace them.

2. Needs Troubleshooting

If sediment buildup isn’t the issue, it might just be that the heating elements or thermostat need troubleshooting. This is a fairly easy procedure for an electric unit, but if you have a gas heater, you’ll need some experience. This is also why we recommend contacting a professional.

If your unit is electric, here’s a brief explanation on how to troubleshoot it:

  • Turn off the power: Turn the breaker to the “Off” position before you handle any electrical components.
  • Access the thermostat: Remove the access panel using a screwdriver. Then pull out the insulation to expose the upper thermostat.
  • Check the power: Use a multimeter and check the wires for signs of voltage. They should all get a reading of zero before you continue.
  • Adjust the temperature: Use a flat-blade screwdriver and turn the arrow indicating the temperature. Try decreasing the temperature a few degrees.
  • Finish up: Replace the insulation and access panel. Once ready, turn on the breaker to restore your water heater.

If the recovery time is still too slow, it might be that you need to replace the heating elements. Or, perhaps your water heater simply isn’t large enough for your hot water needs.

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This Took a While…

How long it takes a water heater to heat up depends on a few factors. As a general rule, gas units are significantly quicker than electric ones.

But sometimes it happens that the recovery time suddenly increases which may be a sign of sediment buildup. In this case, flush the tank, or call a professional for help with a replacement.

How long does your water heater take to heat up? We’d love to read your answers below, as well as any other questions you may have.

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About the Author

Peter Gray

Peter has been a homeowner for 35+ years and has always done his own repair and improvement tasks. As a retired plumber, Peter now spends his time teaching others how they can fix leaks, replace faucets, and make home improvements on a budget.
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