Heaters and power consumption

[PotRoast]

I have a 240 gal tank and bought (3) 300 watt heaters to heat the tank.

Obviously I am pulling 900 watts if they are all on. Wow.


The question I have is how often do those heaters cycle on and off, once the tank reaches proper temperature?

Do you think I am pulling 900 watts ALL day? Maybe four hours of the day? Maybe just 20 minutes?

Finally, do you have advice for more efficient heaters to heat this tank?

Please advise.

[Sploke]

If the heater is fully submerged, then efficiency isn't really a problem...pretty much all the heat they generate is going right into the water. I don't think there's a huge variance between the efficiency of different heater elements across brands. Chances are they are on less than 50% of the time. That volume of water will hold a LOT of heat, so it will take a while for the temperature to drop, although that varies with the ambient room temp. Obviously if the room is only a few degrees cooler than the tank, the heaters won't have to work as hard. So, as far as how much they're actually on, there's no real answer other than sitting there watching it with a stopwatch if you really want to know.

[fsn77]

It's hard to say exactly how often and how long you're running all three heaters. It depends on how stable the temperature of your tank is, which depends on many factors (ambient air temperature, humidity in the room where the tank is, heat given off by other equipment, etc.). It's impossible to really even guess without much more information, but they could be running 10 minutes or less per hour or 30 minutes per hour. If they were actually heating more than 1/2 of the time (greater than 30 minutes per hour for example), that would be an indication, IMO, that the total combination of heaters isn't large enough for the tank they are being used to heat (or that the thermostat in them may not be working properly).

[kcress]

All good info so far. An electric heater is pretty much 100% efficient.

How much they will be ON is entirely up to the amount of waste heat being delivered to your tank at any particular time and the surrounding room temperature.

Waste heat is the heat from lighting and any pumps in your system. All the energy consumed by any pump that is submerged in your system will appear in your system as heat. Some percentage less if the pump in not submerged. As for lighting a lot depends on how close and what type you have.
Another thing is how much evaporation is occurring as this carries great gobs of heat away from your tank and into the room.

The biggest factor is the temperature difference between your tank and your room. During the day with lights on, room warm, etc I would expect your heaters to be OFF almost entirely. During the night - cool room, no lights, cold winter night, maybe several heaters ON continuously. If the heating costs you a bunch then you could try mitigating it several ways.

Lastly, for myriad reasons, it is nearly impossible to set all the heaters to the same temperature. So you will always have one heater come on first. If it is enough no other will come ON. If that one heater can't replace the escaping heat the temp will continue to drop until the next heater comes ON. Etcetera.