Eheim Jager Aquarium Heater Review

I got one of the Eheim Jager series aquarium heaters while reviewing the Fluval Spec III aquarium.  It’s impressive – if they made it a bit shorter, I would use it in our main aquarium (the Spec V). I got the 25-watt version (model 3611090), which is plenty for the small volume of the Spec III.  The Jager series heaters are also available in 50-watt, 75-watt, 125 watt, 150-watt, 200-watt, 250 watt, and 300-watt.

Eheim Jager Aquarium Heater contents from box

Eheim Jager Heater: Features and Dimensions:

From Eheim’s literature and my observation, the Jager series heaters have the following features:

  • Designed for use in freshwater or marine (saltwater).
  • It is a fully submersible design, or you can set it up with the top out of the water (as long as water reaches the minimum fill line)
  • Adjustable set point, from 18° C (64.4° F) to 34° C (93.2° F)
  • Temperature accuracy to 0.5° C
  • Safety feature to shut off the heater if it is not immersed to the fill line.
  • Ability to correct the temperature calibration (by way of rotating the red ring)
  • It comes with a suction cup mount (removable)
  • It has a lamp that indicates when it is heating (located about 1/3 down the glass heating element section.

Eheim Jager Aquarium Heater with suction cup mount attached

I took some dimensions of the heater (25-watt model) as follows:

  • Length (total from end to where the cord exits): 243 mm (9.57 inches)
  • Diameter (at the largest point – the blue temperature adjust dial): 36 mm (1.42 inches)
  • Diameter (of glass heating element section): 25 mm (0.98 inches)
  • Length from element end to min water level line: 195 mm (7.68 inches)
  • Depth of suction cup mount (from glass face to the furthest edge of blue temp dial ring): 47 mm (1.85 inches)
  • Power cord length: 187 cm (73.75 inches)

length of 25 watt Eheim Jager Aquarium Heater

I purchased my heater in the USA from Amazon.  The dial reads in degrees Fahrenheit; I’m not sure, but I suspect ones purchased from countries using SI will have degrees Celsius.

Heater Setup and Impressions:

There’s not much to say about aquarium heaters – they are simple devices and should be easily set up.  This heater meets that expectation.  It has an adjustment dial to set the temperature where you want it.  It is the blue dial that you see – rotate it so that the arrow on the red ring points to the set point temperature you wish to maintain.

blue control dial and red calibration ring on Eheim Jager Aquarium Heater

One unique thing is the Eheim Jager heaters have a way to adjust the heater if it is not reading correctly.  You do this by rotating the red ring.  You will need an accurate thermometer to perform this calibration (I’ve had good luck with electronic thermometers).  If you have your Jager heater set on 75° F and your (separate) thermometer indicates a tank temperature of 78°F, you would perform a calibration to correct this by rotating the red pointer around from 75° F to 78° F (without moving the blue ring).  A guy on YouTube takes 9 minutes to tell you what I just described in a few sentences.  Aren’t you glad you are here instead of YouTube!

One word of warning that is apparent from this design.  When you purchase this heater, you assume it comes from the factory with that red ring set in the proper place (or very close).  There is no guarantee of this.  The factory might not have calibrated, or you may have purchased a returned heater with the ring rotated previously.  All of this is to say that you should keep a close eye on the heater when you first set it up, ensuring it is in the ballpark of what you intend. Not that they are helpful at all, but here are the manufacturer’s instructions.

I have seen some bad reviews on Amazon for this heater, where it was not performing at all as the user intended.  I suspect that the heater came with poor calibration, or even more likely, the user rotated that red (calibration) ring around before they knew what it did, thus ruining its accuracy without knowing it.

I have not used this heater for an extended duration, but have used it for quarantine tanks and such.  It has worked great.  I have used it both with and without a temperature controller. It seems perfectly reliable and accurate even when using no controller.

side view of 25w Eheim Jager Heater

I very much appreciate the construction of this heater.  The glass seems thicker and more durable than the competing Hydor Theo heater I use on the Spec V aquarium. The cord is downright robust – it seems prudent to give a heater a good cord to make it efficient in getting the power where it needs to go. I love that it has a full 6′ long cord – I’d rather have too much than too little.


Cost and Comparison:

Based on the better construction I have described, I think it is reasonable for this heater to be priced slightly higher than some competitors.  Pricing is relatively flat across the range of heat capacities (all in USD): The 50-watt is around $21; the 200-watt is around $32; the 300-watt is around $32.  As a comparison, the Hydor Theo heaters are $23 for the 50-watt and $23 for the 200-watt (strange – the Hydor heaters are almost the same price across all power capacities).

The Eheim Jager heaters are very capable and durable.  I love the construction.  If I needed a large-capacity, in-tank heater for a larger aquarium, I would probably start with this model in my search.  I will most likely always rely on temperature controllers to drive the heater operation; however, the controls on this heater are good enough to be trustworthy if I needed to operate without a controller.

Use in Fluval Spec Aquariums:

As I alluded to earlier, the Eheim Jager heaters (25-watt and 50-watt) do not fit completely submerged in the Fluval Spec V aquarium – it is too tall.  If you were operating your Spec V without a top, you could arrange the tall Jager heater and have it poke out the top some.  I discuss heater options for both the Spec V and III separately.

This heater fits great in the taller Spec III aquarium. You could suction cup mount this heater inside the display section; however, it’s cleaner to put it concealed in the pump section.  If you do this, don’t bother with the suction cups – just lower it down and let it dangle.

Eheim Jager Heater mounted in Fluval Spec III aquarium

If it touches the flow tube or the glass a bit, that’s not a problem. Remember that if you place the heater in the pump section, consider performing the flow tube modification.

Eheim Jager Aquarium Heater below lid inside Fluval Spec III Aquarium

I think the 25-watt capacity is ideal for the small Spec III and that the 50-watt will be overkill unless you keep your home very cold.

packaging for Eheim Jager Aquarium Heater

The bottom line is this: The Eheim Jager line of aquarium heaters have a robust build, are accurate, have been reliable in my use, and are a very reasonable price.  If they made one a bit shorter, I’d use it in our main Spec V aquarium.  I highly recommend it for those with Spec III aquariums or anyone who needs a good submersible heater.

13 thoughts on “Eheim Jager Aquarium Heater Review

  1. I have used Eheim Jager heaters in my tanks for many years and have not had any problems with them. Reliable and accurate once calibrated. I would not hesitate to add it to any setup where it fits the needs of the aquarium.

    1. That’s good feedback. This model keeps coming up in forums for those who are looking for something reliable but not crazy expensive.

  2. Hi. I like your site — one of the better ones I’ve run across. I have recently purchased a Spec V (via Amazon) for a rescue Betta. I am new to this hobby and confess I did not fully realize what I was getting myself into. …I initially purchased a Fluval 50w heater via Amazon – not considering size at all. It was huge, so I returned it and emailed Fluval directly for a recommendation. Of course, they recommended their small preset heater, however the reviews on Amazon for the smaller Fluval heater weren’t promising. I then purchased a Tetra, 50w, preset, submersible heater since it was literally the only fitting heater I could find locally. The Tetra does not keep my tank at a constant temperature, fluctuating primarily between 75-77.3ºF and occasionally cutting off randomly for long periods of time dropping to as low as 71º. As I researched replacement heaters, I kept coming across the Eheim Jagar, Hydor Theo and Aqueon Pro. I found your site and ordered the Hydor (via Amazon) per your recommendation for Spec V. It arrived with condensation inside (as many Amazon reviewers suggest is a problem with this heater). I returned it and have been hesitant to order another Hydor due to the condensation problem as well as other reviews. I thought I might purchase the Eheim 25w until I read more about it (many reviewers saying it is too large). Do you know if the Eheim has become more streamlined in size/design since your review was written in 2017 — or if there is a newer Eheim product that will work for Spec V? All the reviews I’m finding are a couple of years old. Also, what do you think about the Aqueon Pro for a Spec V? …I would highly value your comments as well as those from other readers.

    1. I noticed condensation in our 50w Hydor Theo about 4-5 years ago. It is still going strong – no problems.

      The Eheim is the same size as I reviewed in 2017.

      The Aqueon Pro has decent reviews. I can’t vouch for it personally, but it seems like at this point it might be a good next step for you.

      Please note that all aquarium heaters can potentially break your heart by failing and cooking your inhabitants. That’s why reviews on almost all aquarium heaters are so mixed. They work fine . . . until they don’t. I’d never use a heater on a tank and inhabitants that I care about without a temperature controller.

  3. Thanks, Nate. I purchased a temperature controller and will set it up when I get the right heater. I thought I was getting myself into a fairly inexpensive, low-maintenance hobby but have since learned different. I’ve spent a small fortune already. 🙂 I’ve become fascinated by and attached to the Betta and want to keep him happy and healthy — a day to day journey so far.

  4. Hi Nate. I’ve ended up ordering another 50w Hydor Theo — decided to give it a second chance. Seemed to be the wise thing to do. …Thanks for your very thorough reviews for Spec V owners!

    1. I’m gonna feel awful if the Hydor Theo doesn’t work for you! (I think it will).

  5. I have been using Ebo Jager heaters as long as I have had aquariums….over 20 years now. I currently have three 150W units is my 110 gallon reef tank. I do use an aquarium controller these days to capture any heater failures, but knock on wood, it has never happened to me.

    Btw, on your dimensions, you diameter on the temperature dial is incorrect. I don’t know what the actual diameter is, but I know for a fact is is not 1/8″. I suspect the 36mm is correct and just the inch conversion is wrong. If so, it should 1.42″.

  6. I have seen numerous complaint on these,, mine failed to hold a temp after a yr. After much communication with the manufacturer they sent me a replacement, which had the same erratic characteristics as the old one right out of the box. I put a timer on this one and turned it to max to hold the temp in the tanks with a different brand set lower in case the Eheim failed completely. The lower set one failed after 6 months. Heaters were a lot more reliable when they made them using copper strips rather than the unreliable circuit boards in use today.

    1. You are probably right. My take – ALL aquarium heaters are crap in that eventually they will fail. Usually at the worst time in the worst way (resulting in a nuked tank with everything dead).

      That’s why I use a separate temperature controller on any aquarium heater.

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