How Long Does It Take For a Water Heater to Heat Up?

There’s nothing quite like a hot shower on a cold day or a nice warm bath after an intense workout session. It’s perhaps one of the most relaxing experiences in the world, not to mention all the pharmaceutical benefits a warm bath or shower offers.

All the same, there’s also nothing as annoying as waiting around, unsure of the duration of the wait before that glorious water is finally ready. Worry not, because here’s a quick rundown that will help you answer that incredibly important question - how long does it take for a water heater to heat up?

This depends majorly on the kind of heater you’re using to heat up the water (other factors like atmospheric pressure and room temperature have intentionally been omitted as they aren’t in any one person’s control) since different heat sources certainly outperform others. This quick guide should help you figure out just that.


Another reason you should probably know how long does it take for a water heater to heat up is to alleviate the possibility of Legionnaires' disease (just think of it as the opposite of typical pneumonia - it’s caused by excessive heat, rather than excessive cold).

In this guide, however, you should keep the following in mind:

  • A thermal unit is a measurement of the amount of energy required to raise the temperature of a pound of water by one degree Fahrenheit.
  • The temperature at which water is considered safe is 122 degrees Fahrenheit.
  • 1 gallon of water is equal to approximately 8.3 pounds.

The Gas Water Heater

How long does it take for a water heater to heat up in the event that particular heater is a gas water heater?

An average amount of water held by a gas water heater is about 40 gallons of water, which allows entering of the supply at an average of 70 degrees Fahrenheit (slightly below room temperature). All factors kept constant, a gallon of water requires about 8.7kj of energy to raise its temperature by one degree, translating in about 30 - 40 minutes for the water to climb up by the remaining 52 degrees and be considered safe.

Your best bet for how long it takes to heat up water with a good gas water heater is about half an hour.

The Gas Water Heater



Electric Water Heater

Generally speaking, gas water heaters tend to be cheaper and more efficient than electric water heaters. In fact, as long as you think along those lines, it’s worth noting that electric heaters are also slower than the average gas water heater.

Once again, all factors kept constant, you’re looking at about an hour or hour and a half to heat up about 40 gallons of water from room temperature into the safe zone. However, if you’re looking to improve this stellar performance even further, consider investing in a good rinnai tankless water heater. It’s your safest best at quickly heating water.

That said…

Electric Water Heater



Tankless Water Heater

Assuming you have a good tankless water heater in your hands, completely unflawed and of the top quality, a tankless water heater should do the job almost instantly.

The tankless water heater is relatively new technology, which, unlike other beforehand mentioned water heaters, doesn’t store any water on its own. Since there is no stored water to be heated and in the process of constantly consuming energy, there’s theoretically no limit to the amount of water being supplied and heated as it transfers through the device and straight into the home, you have on your hands an unlimited supply of almost instantly hot water.

It’s a novel idea, and relatively new to the market, but a good tankless water heater is your safest bet for a ready supply of fresh, hot water. That way, you don’t ever have to wait for your water to heat up, and you save lots of energy in the process. All you need is a good tankless water heater.


Solar Water Heater

Solar Water Heater



The solar water heater comes last on the list but is by no means incapable of achieving the desirable results, at times even evenly matching the amount of time required by an electric water heater.

Typically, solar energy is converted to electric energy and this is used to heat up the water, but, of course, your main hindrance is, well, the sun. On a nice, hot sunny day, it should take about an hour to an hour and a half. Better is that you have a backup power source. A dull cloudy Monday won’t affect you in this case.

How long does it take for a water heater to heat up? It really depends on the technology you’re using, but your safest bet is a good tankless water heater - it’s almost instant!

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