Heater Efficiency and Size

[wpeterson]

We have a large 300w heater in our 90 gallon tank, which has enough power to raise the temperature quickly but draws a lot of current (~ 2 amps). It doesn't turn on very frequently, but when it does it runs briefly and turns off.

Is it more efficient to have a big heater running less often, but with more current? Or is it more efficient to have a smaller heater running for longer periods of time?

I'm tempted to turn this heater down to a fail-safe level, maybe 2 degress below my target and add a 200w or smaller heater set at the target level. Would that provide any benefits?

 

[sfsuphysics]

Efficiency wise there's really no difference in size. If you run one big heater or two smaller heaters you're still going to be using the same power (to a good approximation, obviously there are resistive issues with wire going to the heater).

That said, the better way to look at it, is if one heater fails (on or off) how bad will that be for your tank versus 2 heaters where 1 heater fails (on or off)

 

[rygh]

I would definitely do the fail-safe + small heater route.
As mike said, no difference in efficiency.
But two benefits:
1) Much better if the small heater fails on/off.
2) You do not change water temperature as fast. Nicer on livestock.

 

[Seaslugteam]

I think all heater are 100% efficient so it doesn't matter the size. Essentially heat usually the by product of power consumption (you're heating the same amount that you consume).

Using 2 smaller heaters is the way to go due to heater failure. If one of the heater fails on, then it shouldn't have enough capacity to cook your fish (until you notice it). If it fails off, the second heater should have enough capacity to heat the water decently that you have enough time to react.
I think I remember getting 2 heater at about 75% of your temperature difference between the room the desired temperature.

This article is pretty good for a heater wage chart.
http://freshaquarium.about.com/od/heating/a/heatersizeguide.htm

 

[bluprntguy]

Actually better to have a smaller heater. Larger heaters usually have a larger heating element and a larger heat sink. They continue to heat the water after they turn off. If your heater is oversized, that could lead to a larger temperature spike. As others have noted, they can fail and get stuck on and cook your tank.

The article @Seaslugteam posted is pretty good, but remember that saltwater aquariums generally have powerheads and return pumps that are creating heat. The article recommends a 75 watt heater for my tank, but I had a 25 watt heater in there and it kept it a toasty 80 degrees with no problems.