12-28-2013, 07:42 AM
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Originally Posted by Electric
How long did you wait for a temperature rise? It takes about 9000 joules of energy to increase 1 gallon of water 1 degree F. 600 watts delivers 600 joules per second. For 1 gallon to increase 1 degree F you need 15 seconds. With a 180 gallon tank plus a 30 gallon sump, you are looking at about 1 hour to increase 1 degree F. Once you get a few degrees above room temperature, you start to lose some of the energy from the tank to the room, and it will take even longer for the temp to increase. As the temperature difference continues to increase, so does the amount of heat loss to the room. Eventually you will reach a temperature where the heat loss equals the 600 watts your heaters are generating and your water temperature will no longer increase.
I'm running 200 watts on a a 46 gallon tank. The temp is set to heat the water 10 degrees F above room temperature, and the heater is only on about 30% of the time. I have a glass tank with a glass cover. Open tops would lose more heat, and acrylic is a better insulator. I would think 600 watts would be enough if the heaters were in any kind of water flow in the sump.
It's been over a week - I'm maxed out at 82 degrees even with the 2 300 watt heaters at the highest setting.