The Planted Tank Forum banner

heater wattage v. gallons

3807 Views 15 Replies 8 Participants Last post by  tomfromstlouis
Is there a rule of thumb for for determining how much heater wattage is needed?

I have one 300 watt inline heater on my 220g tank and it is clearly overmatched, since it is always on and the temperature does not move up. I have a second filter line for a second 300 watt heater, and this is my preferred approach since it keeps another piece of equipment OUT of the tank itself. But I suppose if I need 1000 watts hanging in the tank, I'll have to go that route.

Will a second 300 watt inline heater be enough to get my tank up to 78 degrees F and keep it there? Is there a more powerful inline heater available? I have canister filters and this seems like the best idea for me, but if you can come up with a better idea, let me know!
1 - 16 of 16 Posts
What kind of fish do you keep and where is the temp now. Could running the tank at 72 be an answer?
Sounds like a lot of heat going somewhere. Is the room temperature extra cool or anything to make the heater work so much? There are lots of specs on heater sizing but I find them dangerous as they are way high for use with the lights and covers I use.
Another thought might be to ask if there is a way you can tell by feel that the heater is in fact heating? Some can fail but still have the LED light show it is heating. If it is heating and you do need more heat, adding a second heater rather than one single very large one is safer. If one heater sticks on there is far less danger of killing the fish than if a single large heater sticks.
Ideally the heater working longer periods before shutting down will make the heater last longer. To many that will seem backward as they think the heater coil will burn out. But in looking at the way heaters fail, I find the first cause is the contacts stick and the second is the heating coil fails due to the stress caused when it heats (expands) and cools (contracts) which causes metal fatigue at the joints.
I like my heaters just big enough to keep the temp up but not so big they can raise it high enough to kill if they fail. I've lost three tanks of fish to heaters and it really is a bummer!
See less See more
Thank you both for your replies.

This tank has altums and they really should have ~78 degrees, although they seem to be okay now. I want their metabolism and health up a bit for weaning them from acidic water, a project that is ahead of them.

The room is on the cool side and could be part of the problem.

I still am curious if anyone knows what wattage of heating can keep 220 gallons above ambient temperatures by 6 or 8 degrees F.
Heating a Tank

Hello Tom...

I think heating is pretty simple. Figure 5 watts per gallon of tank volume up to a 30 G tank. Any tank that's larger, figure 3 watts per gallon.

My larger tanks do fine with two heaters placed at opposite ends of the tank.

Hope this is info is helpful.

read and decide, where is the tank?

heater ratings are ballpark for holding the temp only a few degrees above ambient.

google result #1
i like the link Mike "wkndracer" posted. keeping in mind circulation is the other consideration. Very important to move that heated water around the tank.

2-300w's might be better than a single 1000w.
Okay, this is good info.

The chart wkndracer shows confirms bbradbury's comment.

600w/~200g = 3w/g

Doing the math, a second 300 watt inline heater just might be enough to keep the tank7-9 degrees above ambient. I am going to try it.
The trouble with most charts is that they are simple answers.
Heating can't be a simple answer as it has a lot of variables. How much additional heat is needed depends on how the tank is set up. Cold room, hot room? Lots of air circulation around the tank? LED lights or or really hot lights? How much heat comes from powerheads and filters? How much cooling do you get through evaporation?

These are all things that will change the answer so most charts are not very worthwhile.
If you want a simple answer, go for the chart. If you want a correct answer, you have to do some thinking and know your tank.
I am not afraid of thinking. I THINK that the other factors you mention are in my case not significant enough to throw the second 300W heater out as an answer. If it only gets me to 76 degrees, I can either decide to live with it or stick an ugly in-tank heater into the equation.
While a number of factors can have slight affect overall on tank temps the biggest change (bang for the buck) for me is covering with full lids in the winter. 90% of heat loss is out the top not the sides.

You mention altums in the post OP and while the growth rate slows with lower temps it's not a health issue even for extended durations. Steve has a great write up on this over on the Angels Plus website.
Tom - Are these the tanks in your office? Most office building are on energy management systems. By any chance is the heat turned down very low over night & weekends?
wkndracer: I have read Steve's article on temps and it is what is influencing me to raise them just a bit. A little extra vigor is a good idea if I am going to acclimate these guys to higher pH.

I have glass on top of the tanks, but I have not cut and fitted the back strips since I am not final on my cutout locations. Things should improve a bit when the strips help seal off the top more.

dogfish: These are office tanks and yes my building is especially "green". I am in on weekends and the temps don't feel too different; let's see how this winter goes.

I ordered a second 300W inline Hydor. I am hoping this gets me over 75 degrees at least.
heater wattage vs. gallons

Hi Tom,

I live in SW Florida and we don't see much in cool temps. But I have a 180 gallon tank with a 65 gallon sump filter, tank is stocked with angelfish. They came down with ich a few months back, and I had a terrible time using two 300 watt Jager heaters in my sump to get temp from 78 -85. In fact, it took days. Usually larger tanks can get by with lower than 5 watts per gallon standard, as the larger bodies of water do not fluctuate temps as easy as a small tank. But your ambient room temperature is important, most heaters are only designed to raise a tank a few degrees beyond room temp. If you looking for inline heaters, I would recommend this one :
I used the equation on this page:
As for heating requirements, I recommend 25 watts for every 10 degrees of ambient temperature per 10 gallons you need to raise your aquarium temperature. EX: If your home is 68 degrees and you have a 40 gallon aquarium, to reach a temperature of 78 degrees you would need a 100 watt heater
In my case I figured during the winter my room temp will be about 20 degrees colder than the tank needs to be. This made it easier for me to calculate what size heater I'd need.
FWIW the extra 300 watt heater was successful in raising tank temperature to 78 and both heaters now cycle off occassionally, so I imagine I have a little spare capacity. Don't know if I could raise it to 85F, but that would be temporary if needed and I could just stick a Jager in the tank for a while, so my problem is solved. Thanks all for chiming in.
1 - 16 of 16 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.