Is there anything wrong with getting a heater very undersized for the aquarium?

[bryanfuel]

I'm a bit paranoid about heaters in general. I came home to a 92F tank one day that my zebra moray somehow survived through.

I have a 24G cube in california and I was wondering if there was anything wrong with getting a tiny heater sized for a 5-10g tank and using that to maintain stable temp. I mostly want to stabilize the temp around 78 and the coldest I've ever seen my tank get is 72. My thinking is that, if a tiny heater fails on, it's not going to cook my tank like last time, and most likely will be running 100% duty cycle most the time anyway to heat the tank from 72 to 78. In the future I'd love to do a full controller but not in the budget at the moment.

 

[Quietman]

Thing you have right idea. Maybe a tad impractical though. I have 3 heaters in my system, none of which have wattage to cook the tank on their own. Plus it would take multiple failures to have stuck "on" heater cause atank overheating problem. I do not have controller, no plans for one. Aside from house ac failure/summer power outage (no budget for chiller or generator yet), I'm well protected. It's a balance...not too big to overheat on failure, not too small to require too many. I also run mine a bit lower temps.

 

[maroun.c]

Problem is one alone might run non stop which might cause it to fail sooner.
Having multiple I would advise to run them kn a co stroller so they all shut down together if two shut down 3rd is left running non stop as it cant raise temp of the tank to stop and temp might not drop enough for other 2 to kick on.

 

[siggy]

If your really concerned about over cooking, a tank controller as mentioned ^^^^ or a commercial grade temp controller is also a option, Ranco is is the STD everyone uses. I took it further and grabbed a Penn, back lit and a ton of features.

 

[Dine]

Your idea is right but it’s asking for problems. Get a heater rated for your tank (no bigger or smaller). Undersized heaters don’t operate as intended and it ups the risk of a malfunction. If overheating is a concern (and it should be) your money will be better spent on a temp controller like an inkbird or something more complex like an apex. It’s the only “real” way to prevent that

 

[Brew12]

I run what most would consider to be very undersized heaters for my system. I have 2 heaters, 300W each, on my 187g tank. According to Finnex, they are rated for up to an 80g tank.
My Profilux tracks run time so over the last 2 years my primary heater has run for under 2 hours per day on average (1.7hrs).
My backup heater has run for a total of 48 hours in those 2 years. It is set to come on a degree below the primary heater.

My recommendation is to size a heater based on what your tank needs and not a chart by a manufacturer.

 

[Bryan68]

I run what most would consider to be very undersized heaters for my system. I have 2 heaters, 300W each, on my 187g tank. According to Finnex, they are rated for up to an 80g tank.
My Profilux tracks run time so over the last 2 years my primary heater has run for under 2 hours per day on average (1.7hrs).
My backup heater has run for a total of 48 hours in those 2 years. It is set to come on a degree below the primary heater.

My recommendation is to size a heater based on what your tank needs and not a chart by a manufacturer.

Just jumping in the conversation
since I'm about to buy some heaters for my 180 gallon build. Would you explain how one would derive what the tank needs? My house temp ranges between 70 in the winter and 74 in the summer. What size heaters would you recommend?

 

[Brew12]

Just jumping in the conversation
since I'm about to buy some heaters for my 180 gallon build. Would you explain how one would derive what the tank needs? My house temp ranges between 70 in the winter and 74 in the summer. What size heaters would you recommend?

It's pretty easy to see if you use a controller. It would be harder to guess without the available information

My heaters never run while my lighting is anywhere near its peak. I try to keep my tank at 78F. My first heater kicks on around 77.8F and takes around 30 minutes to get temperature back to 78F. You can see it does this a couple of times a night.

. Mine is in a home office, so that helps let me use a smaller heater. I also run an outside air line to my skimmer so my heater does run more when it is cold, like last night. During the summer my heater may not run at all.

I think you could get away with 300W heaters if you have a primary and backup similar to what I use. I think a good basis is that I want a heater that takes around an hour to go from 77.5F to 78.0F. If your current heater can do that much faster I would consider going down in size.

 

[bryanfuel]

Thanks for the replies everyone! I'll probably get a couple small ones to spread the load around. I don't really want to get an independent controller when I'm hoping to get an apex in the next couple years.

 

[Sleepydoc]

Absolutely nothing wrong with getting an undersized heater and several things right.

If you have 2 heaters it will be nearly impossible to have the thermostats exactly matched, so one will tend to kick on first and/or run nearly continuously, so I would agree with what @siggy said above and add a controller to your heaters - not only is it better when you have multiple heaters, but it adds another level of safety and redundancy.

There are essentially 3 modes of failure for heaters:

1. The element burns out - relatively uncommon IME but if it happens you end up with a cold tank. Not ideal, but in your climate that’s actually a huge concern.
2. The thermostat breaks and won’t turn on - essentially the same as the element breaking.
3. The thermostat breaks and gets stuck on - this is the most common and most dangerous mode of failure.

Now consider the setup where you have 2 smaller heaters - if one breaks, the second will either prevent the tank from getting dangerously cold or it will not overheat the tank (or at least give you more time to catch it before it does.)

Now, add a controller, like the Ranco listed above, and set the controller to 78º and the heater thermostats slightly higher, say 80º. The heater thermostats will never turn off. Since the wear and tear occurs with the cycling on and off, you they are much less likely to fail. The higher-quality relay on the Ranco handles all the switching and in the event that it does fail, the heater thermostats will kick in and shut off before anything catastrophic happens. If, by chance, both the Ranco and one of the heater thermostats fail, you‘re still safe. The only way to really get in trouble is if the Ranco fails in the ON position and both the heater thermostats simultaneously fail in the on position.

 

[revhtree Verified Admin]

Thanks for the replies everyone! I'll probably get a couple small ones to spread the load around. I don't really want to get an independent controller when I'm hoping to get an apex in the next couple years.

This is what you should do.

 

[Phildago]

grab yourself an inkbird controller, a normal temp controlled heater, and an undersized heater. Then you can plug the undersized heater into the wall so that there is no danger presented by it, but it will always run and keep temperature relatively stable. Plug the normal heater into the inkbird, set the heater temp to whatever youd like to keep the tank at and set the ink bird for a degree or two above that temp. This way whenever the temperature drops the normal heater will bring it up to the desired temp, but if it ever malfunctions and the temp is too high the inkbird will cut power to it. Yet if the inkbird cuts power, youll still have the small heater keeping the temp from dropping too low too quickly

 

[EBNewbie]

There's nothing wrong with a tiny heater. It's pretty rare for an element to fail, especially if it's mostly on. If it does fail, you get a colder tank, which is OK.
Heaters usually fail at their thermostat since a bi-metal strip will curl and straighten up to make contact. As with anything, moving parts usually fail first in any equipment.

As others have mentioned, a controller adds redundancy but it's not an option for you so I'd do undersized and take my chances with a cooler tank than a 92F bath.

 

[ca1ore]

Hang on .... it’s a good idea to use multiple smaller heaters versus one large one, but a single small heater rated for a 5-10 gallon tank will likely be insufficient for even maintaining 24 gallons. Depends entirely on the tank/ambient differential.

 

[Bryan68]

It's pretty easy to see if you use a controller. It would be harder to guess without the available information

My heaters never run while my lighting is anywhere near its peak. I try to keep my tank at 78F. My first heater kicks on around 77.8F and takes around 30 minutes to get temperature back to 78F. You can see it does this a couple of times a night.

. Mine is in a home office, so that helps let me use a smaller heater. I also run an outside air line to my skimmer so my heater does run more when it is cold, like last night. During the summer my heater may not run at all.

I think you could get away with 300W heaters if you have a primary and backup similar to what I use. I think a good basis is that I want a heater that takes around an hour to go from 77.5F to 78.0F. If your current heater can do that much faster I would consider going down in size.

Thanks Brew12, you're a wealth of knowledge on here and your in-depth responses are greatly appreciated!

 

[Cory]

I run a 300 watt eheim jager. Its on 24 hours a day on a 200 gallon. Temp stays between 77 to 81 all year.

 

[Sleepydoc]

Thanks Brew12, you're a wealth of knowledge on here and your in-depth responses are greatly appreciated!

Heater sizing is heavily dependent on the system and multiple factors affect it, including ambient temperature, humidity, lighting and other pumps/equipment.

I have a 120 with a 40b sump (total water volume approx 140 gallons) Winter in MN is pretty dry (the dew point is 29º right now) and the temp in the basement is about 66º. During the day, two, 200W heaters can heat the tank 0.5º F in about 12 min. At night when the lights are off it takes 25 min. (And it takes about an equal time to cool off.)

If I do the math, it would take a minimum of about 200 watts of power to hold my system steady at night. Of course if the humidity or ambient temperature change then that number will change as well.

 

[Bryan68]

Good information, thank you! I will do some experimentation.

 

[sesbalders]

This is an interesting topic which I have done tons of research on and my career as a toolmaker makes me probably more qualified to comment on.

Initially, when you fill your tank up with water, the wattage of the heater does matter, it takes 1.16 watts of power to raise 1 litre of water through 1 degree . So assuming that we have a 350 litre tank like me from 0 degrees to 25 degrees c it will take 405 watts. HOWEVER, what we are fighting and will later become clear is the inefficiency in the system, ie the cooling effect of the ambient. This depends on size of tank, thickness of glass, height of tank off of the ground, height of tank location off of sea level. Surface area of glass, surface area of the heater, wattage of the heater, thermal conduction of the heater material with the surface of the water, lid or no lid, flow rate of pump, and the best one of all, surface area of the water on the top level of the water.

In short, I actually don’t think that there is a mathematician on the planet that could actually calculate the heater size required and here’s why.

Once the water reaches the correct temperature it will not come back on until it reaches the lower temperature of the thermostat, however the figure that you are trying to work out is not how many watts it takes to heat the water, it’s actually the amount of wattage it takes to re heat the water, from the point it turns the heater on until it is over heat divided by the amount of energy you need to expend (wattage vs surface area) whilst taking into account the amount of heat your specific take looses per minute.

Here’s the truth:- thermodynamics dictates that water transmitting heat through x thickness of glass at y surface area will lose z amount of degrees per hour. This cannot be calculated accurately therefore. Electrical devices are not working when they are are off also bigger heaters = bigger surface area. Therefore you are better off with a much bigger heater with a bigger surface area heating a smaller body of water for reliability and cost.