Benefit of two heaters

[sphelps]

It would take a while for a tank to cool off enough to cause problems, however for some reason heaters rarely fail in the off position. For this reason two small heaters is better than one large heater, however two large heaters is worse than one large heater. Hopefully that makes sense but ideally if a heater fails in the on position it shouldn't be able to cook the tank. Not so much an issue with external controllers.

[Azzkr]

I run two heaters my self as well i keep one a couple degrees colder just incase the primary one fails, the tank will only be a couple degrees colder than until the primary one gets replaced,

[HarleyC]

I think I see what your saying sphelps - basically if you have 2 large and they somehow both fail, then you get a rapid rise. However, I do have the temp controller, so the odds of all 3 devices failing would be more in line with the lottery odds - no?

[sphelps]

Originally Posted by HarleyC

I think I see what your saying sphelps - basically if you have 2 large and they somehow both fail, then you get a rapid rise. However, I do have the temp controller, so the odds of all 3 devices failing would be more in line with the lottery odds - no?

With two large heaters only one would have to fail on to cook the tank which can happen faster than it cooling off and livestock tends to be sensitive to heat vs cold. Also two heaters means twice the chance of this failure mode. And yes external controller can help prevent it. Usually people set heater temp slightly higher than the external controller temp for added safety.

[HarleyC]

Gotcha.
Cheers!!

[daplatapus]

Yeah, that's why in my mind I prefer several (3-4) smaller heaters. I also have a basement sump that sucks the heat out of my system. If one fails on or off, no big deal. On a 200-300 gallon system, if one or 2 even, get stuck on, definitely needs fixing, but shouldn't cause a catastrophic failure.
But that also means you have to pay attention to your system. You don't want one broken heater to be doing all the heating You should know if they're switching on and off.

[The Guy]

Originally Posted by sphelps

It would take a while for a tank to cool off enough to cause problems, however for some reason heaters rarely fail in the off position. For this reason two small heaters is better than one large heater, however two large heaters is worse than one large heater. Hopefully that makes sense but ideally if a heater fails in the on position it shouldn't be able to cook the tank. Not so much an issue with external controllers.

I totally agree with this thinking and have never had a heater fail off when it dies, I only run a 125w and a 100w in my 90g with a 50g sump and it keeps my system at 80f. I plan on putting an external controller and make everything safer though. So I would say bigger isn't better in this case.