Jager heater not doing its job


I'm really disappointed with my Eheim Jager 100W heater. I had it on either the 36 gal or the 29 a couple years ago but took it out since it tended to "overheat" the tank by going to 80-82F, if I remember correctly. Now I'm giving it another whirl since I have a tank without fish to worry about. Well, instead of going over what it says -- it is like 7 degrees under what it says.

Case in point... room temperature has just dropped to 67 degrees and the tank is at, with heating light on, 72F. About five minutes ago, room temp was 69F and heater light still on... tank at 72F. So heater has maintained the temp of the tank even though room temp went down.

The heater is set for 79-ish degrees F. 72F is not close enough to my desired temperature... 72 is the highest I've seen it go and I check it multiple times during the day as I'm curious to see whether it budged. It's budge involves going down to at least 68, if not 66, and up to 72. 4 degrees of a change is not good for my fish.

Now, this heater is a different version than I've seen many other places. It specifically has a water level line and does not want you fully submersing it. Heater is currently at "water level" line. It has a gray top and blue ring to change the temperature. When I slightly adjusted it, I turned the blue ring to be from 77-78 to 79-80.

What is the best way to tackle this? Turn the heater up even though it is highly inaccurate? Go buy an Aqueon Pro because I'm all for them being much much better (I would get 150W - like what is on my 36 gallon bowfront)? Is the heater just not enough wattage for how cold the house is?

Only other concern would be the tank is about a foot away from the back door. But having my hand go up and down, there is no cold air... so I'm not too concerned about that. The electric heater in the house is on other side of room.


A number of things could be going on with the heater.

One: The heater's internal device is broken, possibly from being submersed then dried out for a while ,therefore causing the heater to malfunction-maybe why it over heated the tank in the past-but with 80-82 degrees I would hardly call that a over heat. I assume you set it at 79 degrees back then. Sometimes heaters have a tendency to be somewhat inaccurate, so you should have turned the dial down and see if the temp goes down.

Two: I would say another factor was that perhaps you didn't allow the heater to soak for about twenty minutes before tuning it on, it is important to do that because then the heater can acclimate to the water. You can also tr placing the heater under the filter output, this will help circulate heat in the water better and prevent one side from being cooler that the other-you should check and see what the temp in on the side of the tank with the heater-that may be the issue.

Three: You said that it is a 100w heater, but is this in the 29 gallon or 36? Either way, 100w isn't really enough for those tanks. I'd say 150w minimum for the 29 gallon-mine is 150w I believe on my 29 gallon-and a 200-250w for the 36 gallon. So the heater isn't strong enough for those tanks. Along with the tank being near a door-constant cool current from outside-and the room temperature is a few degrees cooler than the water. So these factors can cause issues with internal aquarium temperature as well.

So I would check these things first, but all in all I would recommend a stronger heater, jagars are awesome heaters, though I haven't tried the aqueon brand heater, I don't see why those wouldn't work for your aquarium either.


Thanks for the reply.

One is possible. I guess it wasn't overheating the tank, it just was higher than I was comfortable at the time. Right now I would be fine with that temperature since I know I have species that can handle that.

Two - The heater was in the tank for much much longer than 30 minutes. I wanted to make sure I was home before I turned it on.

Three - I originally bought the 100w since the recommendation from Eheim was a 100W is good for 20-30 gal. The next "available" one recommended fro 30-45 was 125W, but that was not available for purchase. I also don't think there was a 150W when I was buying the two Jager's a couple years ago. Of course, now I can't buy them from PetSmart again -- they stopped carrying them.

I do understand now that I should go with a 150W heater, especially with the cooler temperatures of my place.

Whole tank is at 66F - moved thermometer and gave it some time to change if it needed to. Heater has not kicked on at all. Room temperature is currently at 67F.

Next time the heater kicks on, I'm going to put my hand near it and see if it is actually heating or if it just kicks the light on and says it is heating.


It's too bad that petsmart doesn't carry them anymore, I had to get mine online.

To be honest, those watt recommendations aren't always accurate, you just have to do your research and experiment to see what suits your tank best. I only suggested the stronger one since you have cool room temperature. If you lived in an arid area like Arizona, then maybe you could get away with a 100w.

I think that your heater might be broken, so you may be in the right to go get a new one, to bad, but not uncommon.


Yeah, looks like it is going to be a must-buy new heater kind of situation... when the light was on, I was able to touch the heater without it being hot. It wasn't warm at all - or well, maybe a super small amount... but that could have been my imagination.

No where locally seems to sell the Aqueon Pro, so I might end up buying a new Eheim Jager -- both the local stores carry it. And one of those, even though it is a bit more expensive than I would like, I have a gift card for - so it wouldn't really be spending money.


The Eheim Jagers can be calibrated, so it's possible it is just out of calibration.

I do agree that 100W could be under-powered, particularly in a colder climate. I always aI'm for about 3-4w per gallon of water. I currently run 100W Jager on my 20G [5WPG], and I run 2 x 150W (300W) on my 66G reef, which is about 80G with sump, giving me about 3.75WPG

And FWIW, all of mine are fully submersed

The following video explains how to calibrate the Eheim.


You possibly have an old jaguar, the new ones can be submerged


I have the old version - the new ones have a red calibration feature. The box states there is a calibration button but I don't think I've ever touched it.

Either way, the heater has no heat coming from it - even with the heating light on.

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