Aquarium In-Line Heaters

If at all possible I try to keep the aquarium hardware out of sight in the aquarium. I want it look like a natural scene as much as possible. I don’t like to see heaters, probes, etc. I use black PVC, PVC fittings, and airline tubing inside the tank to make it blend in with the background. To hide the heaters, I decided to build in-line heaters. Basically, a heater and temperature probe inside a 2” ABS pipe put in-line with the filtration system. This would allow for efficient heating of the water and keep the heaters out of sight.

For this aquarium I figured that I would need about 600 watts of heating. I found these titanium heaters on Amazon, so I bought 2 – 300 watt heaters. These do not have thermostats in them, so you have to buy one separately or have some other way to control the temperature. I bought these because they didn’t have a thermostat built-in and I used my Apex Jr. Due to limited space behind the aquarium, I decided that two short ones would be better than one long one. I was hoping that they would thin enough that I could put them side by side inside the ABS pipe. Unfortunately, they were too fat with the rubber ends, so I decided to make two in-line heaters one for the filter intake side and one for the filter return side. That way they would be short enough to not interfere with other components.

**On a side note, after I bought these I thought that it might actually be better to have heaters with thermostats as a fail-safe. The thermostat would be set a little higher than the intended temperature of the aquarium, but not so high that it would kill the fish. This way if the main temperature controller failed, the fish wouldn’t be cooked. I thought a fail-safe was such a good idea that I ended up adding my own (add link to post).

The black pipe is a 2″ X 24″ ABS sewer pipe that I bought from the Home Depot. The 300 watt titanium heater is on the left and the Apex Jr. temperature probe in on the right.
I cut the ends off the cords and then drilled holes in the pipe just barely large enough to pass the cords through from the inside out. On the right, I added another temperature probe for the heater fail-safe and a grounding probe. I drilled a separate hole for each in the pipe.
I drilled the hole close to the end so I could get the cord through. I put the heater in bottom first so it would fit better.
I put the Apex Jr. temperature probe in the same way as the heater. Then I pulled the cords tight, and sealed them with silicon aquarium sealant. I really goobered it on there to make sure that it wouldn’t leak.
**An important side note, if you use a two wire cord and there is a crease down the middle of it where the two wires meet, make sure that you split the wires apart at the pipe and put sealant in-between the two wires. I didn’t do this on the first heater I made and even though it was sealed well there was a micro bead of water that found its way through the cord and made a small puddle on the floor.
The second heater was smaller because I didn’t put a temperature probe in it. I didn’t have as much vertical space on that side of the aquarium, so it was good that I was able to make it smaller.
Special glue has to be used to glue ABS to the PVC fittings. Using normal PVC glue will not bond correctly.
The PVC pipe fittings dry fit in place, I put 3/4″ MFP X 1″ I.D. tube fittings in the ends.
On the return line end, at the top, I put a flow meter that connects to the Apex Jr. This allows me to monitor the filter system flow, so I know when to clean the filter.
After the sealant cured for 24 hours, I used these crimps to re-do the Apex Jr. temperature probe connection. I had to buy a special crimping tool and connectors because it uses the small telephone handset (4P4C). It only had two wires, so it was pretty easy to do. I ended up with 100 connectors because that was the smallest package I could find on Amazon.

I used cord repair kits to put the plug ends on the heater cords.

This is a blurry picture of the first in-line heater that I made and installed. I forgot to take pictures of the new ones before I installed them, and there isn’t enough room back there to take good pictures. This one wasn’t powerful enough to adequately heat the aquarium, it had a single 300 watt heater in it.

I keep the aquarium at 83 degrees. I’m able to keep the temperature within about 0.2 degrees.