Heater position and placement


Hey, just curious as well to put the heater beside the filter, or on the other side, I've heard both sides, and was just wondering what the general concensus was. Thanks,



I put mine where there is the strongest current - or the most water flows past it. i've heard that many people put it under the gravel to hide it, but then i've also heard that that can overheat certain types of gravel, 'causing it to explode... or uneven heat distribution, that can cause the glass of the tank to crack. i'd rather have an unsightly heater showing than a potential crack in my tank!


The Rena heaters will attach to the intake for your filter, so it heats the water as it flows into the filter.....


mines in the middle at the back at roughly 30 deg to the horizontal (with my thermometer at the furthest point0 which will be hidden behind some wood...seems to be keeping my tank at the desired temp 26 deg guess I'll find out when its cycled and I add fish.

FL CommunityFans

Filter in the middle... heater far right.. thermometer far left.


For my smaller tanks I just kept mine in the back right corner (filter being in the back left) with an airstone nearby. For the 75 gallon right now I have two, one in the middle of each half horizontally. The plan was to keep them a little close to the surface to make adjustments easier than place them closer to the gravel, out of view but I've been too busy watching the tank to do that yet.

I don't think it really matters where the heater is for the smaller ones but for larger tank a lot of people do suggest two heaters, one on each side.


It doesn't seem to matter where we put the heaters since we have all smaller tanks.


Looking around at the LFS and looking at pictures on the web, I've noticed most tanks have the heater attached to the center back of the tank at an angle.

What's the reason for this? Better circulation?

I have mine almost in the corner of my tank. Should I move it?


I really don't know, mine is in a corner too... but I guess that's the reason?


The heater should be in a location that has flow, so as long as the corner has some flow you don't need to move it.

Ok a little more on heaters
Heaters have a thermostat which is located at the top of the heater, now if the heater is in the vertical position, then as the water is heated, it will rise.... ( You can see this when the heater is on, you will see a haze around the heater that is going up.) With the heated water going up, it will warm up the thermostat and switch the heater off once the water around it has reached the set temp.
Now if the heater is say on a 45 deg angle on the back of the tank then the thermostat will be measuring the true tank temp, ie not affected by the water coming off the heater.
By having the heater set up in the 45 deg, the heater won't be switching on and off all the time and may last a lot longer.


By having the heater set up in the 45 deg, the heater won't be switching on and off all the time and may last a lot longer.

Now that makes a lot of sense.


Good eye fishylp..I've noticed that but never thought anything about it. Good piece of info.


Just a followup. I'm still cycling my tank and am keeping the temp kind of hight to help cycle faster.

I had the heater vertical and the water temp was consistantly at 82. I shifted the heater to about a 45 degree angle, didn't touch the thermostat. The temp is now consistantly at 84 and the heater does seem to run for shorter amounts of time. I don't have a stop watch out, but it seems that way.

Works for me, should work for you.


I moved my heater out of the corner of my 20 tall and centered it on the back wall. I felt like this would more evenly heat the tank and keep a steadier temp. Is this an accurate statement? It is harder to hide which I don't like, but if it is more effective I'll leave it.


Yes, this is more effective.


best place is by your filter so the heat gets spread around.


I place mine right next to the filter intake, my thinking is it will get sucked up into the filter then spread though out the tank.

Dezz Houdini

HI Fellow Fishy people,

My heater is placed on the inside-back of my tank at a diaganal position so as to evenly spread the heat, however after looking at a few aquarium pics on the photo section I don't seem to see any one elses heaters....

so the question is, can I put it in a more hidden location or is it just the type of heater I have?


My heaters show in all my tanks. I have them sideways or at an angle in the back same as you. Maybe it is the angle of the pictures? Or maybe there are decorations placed so the heaters aren't so obvious.


yeah mine all show in my tanks too top right corner of most


I put mine right in tne center. It blend's in good with the background.


Generally I place the heater vertically and in the center. I have the power heads from the UG filters positioned to set up a circular current in the tank. But there is something to be said for having the heater set up so there are warn and cool spots in the tank, letting the fish choose the most comfortable spot for them.


Mine are all on the back wall diagonally. They are very obvious, except in my bettas tank where it is mostly covered by a fake plant.

Dezz Houdini

Maybe I just haven't noticed because of all the lovely fish


I am finally getting to set up little man's tank and am wondering if it is OK to position the eheim Hager 50w heater horizontal and down near the substrate. The instructions say to mount it vertical but it is too long for the tank. In my research I've seen heaters mounted horizontal but wasn't sure if those were a special design or something. Thank you for helping this newbie



My Jagers are horizontal in my sump. I've never had an issue. In your tank, horizontal will give better even heat distribution.


Thanks Is it best to put the heater closer to the top or can it sit lower near the substrate?



It really makes not a lot of difference. Heat rises, so I'd say bottom is most efficient.


Thank you very much Everything else is in place and I really want to get this finished today since the tank was supposed to be a birthday gift. The kid's birthday is tomorrow lol. At least it will be cycling for his birthday.


Sweet! The last few little bobbles and delays are so infuriating! Try your best to fill the tank with water that is close to the temperature you want. Saves time. And wait 24 hours between temperature adjustments as you fine tune the heater.


I'm kinda big on following manufacturers instructions. I too have a heater that is too long for the tank, which the instructions say to keep verticle. So I put it diagonal so the bottom is just above the gravel and top just below the surface.


I tend to do large W/Cs, and one big advantage of having the heater near the substrate I find is not having to unplug the heater for fear of exposing it during a W/C.
Other then that, given that most people over filter, and therefore have very good water flow, I don't think that positioning really matters much to even heat distribution.----rick

Although it goes against the grain of most guys (I know, sexist comment) to read much less follow package directions, I do agree with jdhef that following the manufactures instructions is generally a good idea. For example, I found that once I started to do so, the phenomena of manufactures always providing 'extra nuts and bolts' disappeared overnight.


Thank you for the responses. I just stuck it to the tank diagonally. Figured I would be moving it at some time before fish came home anyway, so if it was wrong I could change it then.


If I added a 10 gallon sump tank could I just put the heaters in that so I don't have an eyesore in the display tank?


Interesting idea. I've never had a sump so I don't know. But I don't really see a reason why it would not work.


Yes. This shouldn't be a problem, just make sure you measure temperature inside the sump and in your fish tank and adjust accordingly.


Yes that is one of the main benefits of having a sump. Also, remember to factor in the amount of water in the sump into your total water for your system for estimating what size heater to use, or treating with any chemicals.

For example, if you had a 10 gallon sump for a 50 gallon tank, you have 60 gallons in total. So you want a heater for a 60 gallon tank, and add enough chemicals for a 60 gallon tank, etc.


Maybe this is an arbitrary question, but I'm wondering... Is there a "best" way to position a heater in a tank?

Horizontal or vertical?
Back wall vs. side wall?
At the bottom near the substrate or in the middle?
Near the filter intake or away from it?
Does it depend on tank size?

Just curious :sly:

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well I can only answer some of the answers.

first under the intake is surely good!

and I like to put it horizontally, secondly, yes it depends on the tank size. if u have a 50 watts you obviously can't use it in a 50 gallon tank. yup!

sorry I am not that big help.

Sarcasm Included

Horizontal (keeps the heater in the water during large water changes)
Personal choice(as long as it fits and has circulation)
Near bottom(heat rises)
Intake or outflow is up to you(I prefer out flow, but it wouldn't work for a drip system)
Tank size doesn't matter only water flow.


You want it in a spot with good water flow to provide even tank heating.
I keep my heaters vertical, but that's preference. I have one at each end of the tank to provide even heat.



I was just reading a post about heaters maintaining the water temp too high for what they are set for. It has made me wonder if my heater placement is positioned ok? I have to keep turning the heater setting down to maintain 80 deg in my 5.5g Betta tank. Initially 3-4 weeks ago when I got heater, set it at 79 for 80 deg water. Now set at 72 for 80 deg water. Is it my heater location causing heater temp setting to be off? I am starting to think it is the heater?Heater is mounted diagonal under filter outflow into tank. Should I move heater perpendicular beside intake tube instead? Just trying to get even heat throughout tank. 25w Hydor Theo


Honestly, the heater is not the best of quality and probably contributing to the adjustment not showing exact temps. It could be the placement of the heater as well - you could try moving it opposite side of the filter and place your thermometer in the middle of your tank and see if that makes any difference.

If you are so inclined to get a more accurate heater, I would go with the Aqueon pro for accuracy



HI Fishrfriends,
By the look of the photo your heater isn't fully submerged in the water, I believe that is dangerous and also it might be where you are loosing heat from it. If you still have the box it came in check that but all heaters should be fully under the water guage and all. I can't see any problem with the heater being near the filter though. As long as the thermostat is on the opposite side of the tank to the heater.


Junne, thxs. I have an Aqueon Pro in my 29 gallon and really like it. The lowest wattage in the Pro is 50w, Would that be too much for a 5.5g tank? Any other heater recommendations if 50w Pro is too much?
@SB, thxs also. The heater glass is always completely under water and half way up on heater plastic top portion.
I can lower heater and see what happens. Sorry, but I do not understand the loosing heat? The heater is set at 72 and water temp is 80deg and heater still comes on.

Guess bottom line is prob get new (better) heater, completely submerge it, experiment with placement and keep close eye on water temp... I will do whatever needed to keep my tropical fish Betta from being a hot tub fish.


HI again,
I thought you might be loosing heat from the top of the heater because its not fully submerged in the water... I see you are from the USA so heater brands here in Australia might differ from ones you have there so I can't suggest a heater for you.
All I can say is fully submerge your heater top and all in the water


Oh you are right - might be overkill by 25 watts. I don't know that it can be used or not.
I don't know of another recommendation - sorry, I hope someone else can find an answer for you

As far as the submersion of your current heater, as long as the line on the glass has water over it, which it appears to be, it is fine and the entire thing does not need to be underwater.


Thanks again Junne and Sabrina Brook. Time to start doing new heater research again...


I just bought a 20 gallon tank that I'm starting to setup. It is a high one and has LED lighting. I was wondering if there is a special place that the heater has to go. I have a cut out on the cover and if I put it there it will be next to the pump but a friend told me that it has to be away from the pump. Is that right. Also does it matter how long I keep the lights on. I was thinking about 10 to 12 hours a day.


Heater near the pump is good, it regulates the tank better due to the flow, as for lighting it depends, that long may cause algae growth, depends on planting ect. How do you plan to cycle the tank, fish in or fishless?

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