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In the article below we’ll show you how long it takes for aquarium heaters to heat some of the most common fish tank sizes.

You’ll also learn where to place your heater so that your aquarium water heats up evenly and quickly.

Lastly, we’ll share a few safety tips you should be aware of.

Let’s begin.

Great Heaters To Heat Your Fish Tank Fast!

How Long Does It Take For A Heater To Warm Up?

On average, it takes between 25-40 minutes for a heater to warm up the water in a fish tank completely.

That said, aquariums come in different sizes, and each size requires a different amount of heat and time to warm up.

However, before your heater can warm up the water in your aquarium the heater itself needs to warm up.

Below we’ve shared the time each heater size will need to warm itself up and not the aquarium.

  • A 10-25 watt heater and takes around 40 minutes to heat up completely.
  • A 25-75 watt heater and will need about 90 minutes to heat up completely.
  • A 75-100 watts and around 120 minutes to heat up completely.
  • A 125-140 watt heater and will take about 150 minutes to heat up completely.
  • A 200-watt heater and 180 minutes to heat up completely.

Curious about how much power your heater will use? Check out this article about how many watts your fish tank heater will use.

Once the heater has warmed up it will begin to heat your aquarium.

So let’s look at how long it will take for your heaters to warm up different sizes of aquariums.

How Long Does It Take For An Aquarium To Warm Up Completely?

On average, it takes 24 hours for the water in an aquarium to warm up thoroughly.

However, each aquarium can heat up fast or longer depending on the size and whether or not you have more than one heater.

The timelines below reflect average heating times based on one heater installed in the aquarium and sized according to standard practices.

  • The water in a 5 gallon fish tank takes around 15 hours to warm up thoroughly.
  • The water in a 10 gallon fish tank takes about 24 hours to warm up thoroughly.
  • The water in a 20 gallon fish tank takes around 30-36 hours to warm up thoroughly.
  • The water in a 30 gallon fish tank takes about 48 hours to warm up thoroughly.
  • The water in a 50 gallon fish tank requires a minimum of 60 hours to warm up thoroughly.

Why Do You Need To Heat Your Aquarium?

Maintaining a consistent temperature for your fish reduces stress and promotes healthy fish.

This is why your aquarium’s temperature is vital to ensure the fish’s comfort and well-being inside.

The body temperature of your fish is directly dependent on the temperature of the water they are in.

If the water’s cold, your fish adapts accordingly.

Unlike humans and other mammals, fish do not have the luxury of producing their body heat. If the water temperature dips too low, it can be problematic to aquatic life in your aquarium.

It’s important that you learn how to use an aquarium heater properly.

Where Should You Place Your Heater For Optimal Heating

Most fish tank heaters are generally submersible. However, if indicated differently, they can be installed in different places inside the tank.

If you have a high and narrow tank, installing the heater horizontally close to the tank bottom is best.

This is because warm water rises to the top.

However, if you have a short and wide tank, you should install the heater diagonally to keep it fully submerged underwater.

Do your best and don’t install the heater vertically at the sides of the tank unless it is close to the filter intake.

Installing your heater vertically will drastically slow down the spread of warm water to different tank areas, which is not good for your fish.

Related: Learn more about aquarium heater placement.

Which Heater Will Heat Your Fish Tank Quickly

All heaters will indicate on their packaging the size of the aquarium that they are designed to heat.

Using the right heater is important to ensure that the heater has enough power to consistently maintain the temperature in your aquarium and heat it as fast as possible.

Using a heater that is undersized could cause issues with the heater running too long, pockets of hot/cold water, and even heating times that are more than double what was mentioned above.

Below are the recommended heater sizes for a few common aquarium sizes.

  • A 5 gallon/20-liter tank requires a 25-watt heater.
  • A 10 gallon/40-liter tank requires a 50-watt heater.
  • A 20 gallon/80-liter tank requires a 100-watt heater.
  • A 50 gallon/100-liter tank needs a 200-watt heater.

Larger tanks may require multiple heaters to keep the water warm.

Installing Your Heater So It Heats Your Aquarium Properly

Before installing the heater you should set it to the required temperature (74-82 degrees Fahrenheit or 23-28 degrees Celsius).

You can set the necessary temperature by using the dial on the thermometer.

Note: Keep in mind some species of fish have very specific temperature ranges. Always do your research about your specific fish species to set the ideal temperature.

To get the most efficient heating from your heater read this: Aquarium heater placement vertical or horizontal? you’ll learn why you should install it diagonally or horizontally close to the intake of your filter or next to a bubbler.

this will help disperse the heat quickly and evenly throughout your aquarium.

Important Safety Tips

  • It is always best to use heaters as a backup to avoid sudden temperature drops if either one of the heaters malfunctions. For example, you can use two 25-watt heaters for a 10 gallon fish tank.
  • Always check the thermometer to ensure that the heater is performing as per your expectations.
  • When doing a partial water change, ensure that the water level does not drop below the heater’s minimum water level indicator.
  • Unplug your heater after use. Allow it to cool for 30 minutes before removing it from the tank.
  • Once installed, keep the heater inside the aquarium for at least 30 minutes before plugging it in.

Video: Three Ways To Heat Your Fish Tank

Here is a great video from NW Aquahobby that shares three ways you can heat your aquarium. Surprise they don’t all use heaters.