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Aquarium Heater Types & Watts Per Gallon

An important aspect of your aquatic life’s health is ensuring they have stable water parameters, to include temperature.  There is a wide array of heating solutions to provide the optimal temperature for your aquatic friends to thrive.  Let’s dive in to navigate the options for home hobbyists!

The most common types of heaters are used to heat an aquarium, an outdoor pond or an aquatic reptile terrarium. Heaters have evolved over the years, getting smarter, more efficient and more reliable! At Petco we offer some of the best heating options: hang-on-back, submersible and for our outside ponds, a de-icer!

Hang-on-back (HOB) refers to the positioning of the heater; needing to keep the dial mechanics above water for safety and proper functioning. This type of heater is most widely used in the fish aquarium setting where there is a full tank of water. HOB heaters may not be the best option for nano aquariums, aquariums with low water levels or aquatic reptile terrariums.

Submersible heaters allow you to have a lot more freedom regarding placement within the desired aquatic setup. They come in a compact form, as well as the standard size and are easy to hide behind various décor. The ability to submerge a heater allows you to place the heater horizontally along the bottom of the aquatic environment, making this type of heater attractive for tanks that have water levels lower than a few inches from the top.

Both heaters mentioned above come in two types:

Automatic/Preset Heaters

These heaters are usually set to a safe range of 76-82, taking the guess work out of dialing in the temperature. They are programmed to achieve a listed temperature rated for a defined amount of volume of water.

preset submersible aquarium heater

Manual Dial Heaters

These heaters are more for a hobbyist who needs the ability to have a little more freedom of temperature. They usually allow the user to dial in a temperature range of 68-88 degrees, through a basic mechanical knob.

manual submersible aquarium heater


De-icers for your pond are for a very specific enthusiast! At Petco, we know how important keeping your outdoor pond temperature at safe levels during the winter months is. We offer a wide range of pond de-icers to accommodate your pond size needs. A pond de-icer does exactly what it’s called, it de-ices your pond! This is crucial beyond warming the water as it allows vital oxygen exchange to occur through the openings in the ice it will create, unblocking the barrier between outside air and the pond water.

de-icer for pond

How Many Watts Should I Use Per Gallon for my Aquarium Heater?

I know what you’re thinking, “okay, now that I know what type of heater is best for my setup, why are there so many wattage options?!” Well I’m glad you asked! The wattage of a heater has a direct correlation to the gallons of actual water in the tank. Most modern-day heaters take all the guesswork out of the math but let’s go over it, just in case! In an average household that is around 70 degrees Fahrenheit, you will need roughly 3 to 5 watts per gallon of actual volume. What this means is if you have a 20-gallon tank and your gravel and décor displace 2 gallons, your actual volume is 18 gallons of water (20 – 2 = 18). If we multiply that by 3 to 5 watts per gallon, you’ll need a heater with a wattage between 54 – 90 watts, making a 75-watt heater an ideal option.  If you need your aquarium to be warmer, closer to 82 degrees, or you live in a cooler area, you might opt to closer to the 5 watts per gallon rule making a 100-watt heater a better option.

Important Tips for Aquarium Heaters

  • Getting a heater with too little wattage or at the bottom end of your wattage per gallon ratio could cause the heater to have to work very hard to keep up with the temperature. This could lead to unnecessary stress for your aquatic life due to water that is too cold or even premature failure of the heater. On the other end of the spectrum, having a heater that is too strong can make a warm pocket around the heater in your tank and even potentially overheat the water in the aquarium!
  • There are times though when more is better!  When you have a large tank that has a high volume of water, it may be more efficient and healthier for the inhabitants to have multiple heaters to help warm more areas at once. When using multiple heaters, you can use the same watts per gallon formula, but then divide the number amongst the heaters. For example, instead of one 300-watt heater, two 150-watt heaters placed on opposite sides of the aquarium are a more functional and efficient way to provide a consistent temperature for your aquatic life.
  • Validation and consistency are key!  Whether you have an automatic/preset or a manual dial, it is always good to validate they are working as intended with a trusted thermometer to measure the temperature of the aquarium water.  Remember, never change your aquarium’s temperature more than 1 – 2 degrees in a 24-hour period to prevent stress and temperature shock!
  • Catching the flow! A best practice is to place your heater near filters or areas of higher water flow to help spread the heated water more evenly throughout your tank. However, try not to have it too close to any items that it could potentially heat up and warp/melt!
  • Safety first! When installing your heater, wait 20 minutes before plugging it in to prevent the glass housing from cracking.  Additionally, before performing a water change or attempting to touch the heater, be sure to unplug it and let it cool for approximately 20 minutes. If a heater is exposed to air for too long it could potentially overheat and accidently burn you or the glass housing could crack.

Understanding the impact proper temperature has on your aquatic life and selecting the best heating element for your tank will help ensure they swim happily ever after! 

Reviewed by Don Spaeth, Petco’s National Aquatic Care, Education and Programs Manager

Don is Petco’s National Aquatic Care, Education and Programs Manager. He is an avid aquarist who has worked with and cared for freshwater and marine aquatic life for over 40 years. Throughout his 27+ years with Petco, Don has actively been involved with our aquatic vendor partners and worked to promote aquatic education both in store and company-wide.