Regulating aquarium temperature is important from a stability standpoint of trying to maintain an environment in your aquarium that matches a natural tropical reef. With varying climates around the globe and many of us keeping air temperature inside our homes somewhere around a constant 70° F. for comfort sake, accurate heater function you can rely on is important to maintain those tropical water temperatures of 75-78° F. inside your aquarium.

We took 5 popular aquarium heaters off the shelf and tested them for 24 hours to see exactly how close they can maintain water temperatures to the 78° F set point right out of the box. The results will surprise you with variances as much as 3° F!

Top 5 most popular aquarium heaters at BRS

The experiment

We chose the top 5 most popular aquarium heaters on our website to perform our test. We used the 300 watt size to sufficiently heat our 60 gallon test tanks.

Cobalt NeoTherm

Finnex TH Deluxe with Inkbird Temperature Controller

Finnex HMA-S

Eheim Jager

Finnex HPG

Each heater was set to 78° F., placed into a 60 gallon test tank and then powered for 24 hours. We monitored both the water temperatures and power consumption using a Neptune Systems Apex with a calibrated temperature probe for the last 5 hours. This gave each heater the necessary time to heat and maintain the water temperature and ultimately provide the most accurate data to gauge the heating element accuracy.

A single EcoTech Marine VorTech MP10 pump was left operating through the entire test to create some water movement and eliminate localized hotspots around the heater. The VorTech speed was set at 100% in constant mode.

Ambient water temperature in 60 gallon test tanks inside BRS lab

We recorded an average baseline water temperature of 70.9° F. before adding the heaters using our Apex in each of the test tanks. This baseline temperaturer of 70.9° F. was calculated as an average over a 48 hour period inside the BRS Lab.

We already know that each heater will perform differently, even multiples within the same brand will likely have different degrees of accuracy. This is because of varying thermostat technologies, batch approach to calibration processes and individual quality controls among the different manufacturers.

We are not looking at which heater is best rather if it safe to trust any heater right out the box to maintain accurate temperatures around the set point.

Cobalt Neotherm heater test results

The results

The Cobalt Neotherm was able to stabilize the water temperatures at an average of 77.8° F. To save you the suspense, this variance of only 2/10 of a degree was the best performance we saw among the 5 different heaters which also aligned with what we discovered in our previous video BRStv Investigates: How accurate are heaters and which one is the best?.

Being the top performer in all our tests, it is safe to say the Cobalt Neotherm is one of the most trustworthy heaters right out of the box in terms of being able to maintain water temperatures accurately.

Finnex TH Deluxe Titanium heater with Inkbird Temperature Controller test results

The Finnex TH Deluxe Titanium heating element does not have a built-in thermostat or thermometer. Instead, this heater relied on the Inkbird Temperature Controller to power it on and off. The Inkbird controller does allow you to adjust the temperature variance which means you can control how many degrees between when the heater turns on and when it shuts off with the lowest differential of 1° F.

Looking at the data you can clearly see the 1° temperature swings with an overall average water temperature of 77.1 °F. through the last 5 hours of operation. Something to consider here is this Inkbird Controller is one of the few options that has the ability to be calibrated which gives you the ability to further improve this heaters performance.

Finnex HMA heater test results

Moving on to the Finnex HMA-S 300 watt heater which allows you to set the temperature using an analog controller and manages that temperature using an internal thermostat housed inside the rubber top of the heating element itself.

During the last 5 hours of operation it maintained an average temperature of 76.4° F., just over 1.5 degrees from our target set point of 78° F.

The graph displays something interesting in that the Finnex HMA thermostat held a tight temperature swing of only 2/10 of a degree around this 76.4 average but still came in at 1.6 degrees below the target.

Eheim Jaeger heater test results

The classic Eheim Jager has a more traditional style of temperature setting and adjustment with a bezel ring on top in which you align the red arrow with your desired water temperature.

The Jager maintained a temperature average of 76.1° F. through the last 5 hours of operation which is almost a full 2 degrees below the target.

Perhaps the reason this is one of the most popular aquarium heaters of all time is due to the fact that they recognize that each heater will not always be 100% accurate out of the box and give you the ability to calibrate using the red and blue rings on top. One of only two heaters we tested with this calibration capability.

Finnex HPG heater test results

The last of our test heaters is the Finnex HPG 300 watt titanium heater with a built-in digital temperature display and push button controller and external temperature probe. The external temperature probe is nice so you can remotely place the probe away from the heater to get a more accurate reading of your tank's water temperature.

For accuracy, the HPG was the least accurate with almost a 3 degree variance below our setpoint with an average temperature of 75.2° F. through the last 5 hours of operation. This really goes to show the importance of accounting for temperature differences with brand new heaters off the shelf.

Reef fantasy scale

Can you trust your aquarium heater right out of the box?

After today’s experiment we give this a 2 on our Reef Fantasy Scale because out of the 5 most popular heaters on our site, only one of them proved to maintain temperatures within an acceptable range of the set point.

Most reefers would prefer to see better performance from some of these heater but it is a reasonable expectation to assume there is a balance between quality and cost.

In other words, it is not surprising that the best performing heater also has a price tag of about 3-times the average which certainly reaffirms the notion of “You get what you pay for” and the fact that buying quality equipment up front will save you headaches in the long run.

Eheim Jaeger heater calibration dials


With the goal of accurately creating a very natural like environment for your fish and corals, it is critical to find a way to account for the larger variances by either calibrating or offsetting the temperature setting to account for the difference.

Heaters with a calibration feature such as the Eheim Jager and Inkbird Temperature Controller make this much easier and eliminate any guess work around what temperature set point is appropriate to maintain the target water temperature of 78° F.

Neptune Systems APEX

Today’s discussion revolved around the standalone heater and feature set right out of the box. Any one of these heaters could be utilized with a temperature specific controller like the Inkbird or comprehensive aquarium controller like the Neptune Systems Apex to determine the ON/OFF cycles. These controllers also have the option of being calibrated fairly easily and in the case of the Neptune Systems Apex, remote monitoring, alarms and email/SMS alerts.

To learn more, check out Ryan’s video about the best heater strategy for a simple and stable reef tank which explains how and why it is so important to set up and control your heater properly and with careful attention.