From: http://www.beananimal.com/articles/thermodynamics-for-the-aquarist.aspx
Q: How much heat does my submersible pump add to the aquarium?
A:For our purposes, almost 100% of the energy consumed by a submersible pump (mag-drive, powerhead, etc.) is converted to heat in the tank! The simple fact is that if you were to take a heater that consumed exactly 100W and a powerhead that consumed exactly 100W and placed them each in a 5 gallon bucket with a lid, both buckets would reach the same temperature in the same amount of time! Why? Much of the energy consumed by the pump is directly shed as heat into the water. What is left does work and that work (moving water) causes friction (water moving against the objects and walls of the tank), most of which is converted to heat in the tank. When attempting to calculate the heat load on your tank, you should add up the total wattage of all submersible pumps in the system!
Q: How much heat does my external pump add to the aquarium?
A: This is not as cut and dry as a submersible pump. Different styles of external pumps contribute different amounts of heat into the system. Some external pumps are cooled by the water flowing through them (most mag-drive pumps). Most Jet style centrifugal pumps are fairly well isolated from the system and may only shed 5%-25% of their heat into the aquarium (remember they move water and create friction, no matter what). Is there a rule of thumb? Not that I know of! I would assume maybe 80% heat transfer for external mag-drive style pumps and 15%-25% heat transfer for other external pumps, especially if they are located in a closed stand!
Q: How much heat does my submersible pump add to the aquarium?
A:For our purposes, almost 100% of the energy consumed by a submersible pump (mag-drive, powerhead, etc.) is converted to heat in the tank! The simple fact is that if you were to take a heater that consumed exactly 100W and a powerhead that consumed exactly 100W and placed them each in a 5 gallon bucket with a lid, both buckets would reach the same temperature in the same amount of time! Why? Much of the energy consumed by the pump is directly shed as heat into the water. What is left does work and that work (moving water) causes friction (water moving against the objects and walls of the tank), most of which is converted to heat in the tank. When attempting to calculate the heat load on your tank, you should add up the total wattage of all submersible pumps in the system!
Q: How much heat does my external pump add to the aquarium?
A: This is not as cut and dry as a submersible pump. Different styles of external pumps contribute different amounts of heat into the system. Some external pumps are cooled by the water flowing through them (most mag-drive pumps). Most Jet style centrifugal pumps are fairly well isolated from the system and may only shed 5%-25% of their heat into the aquarium (remember they move water and create friction, no matter what). Is there a rule of thumb? Not that I know of! I would assume maybe 80% heat transfer for external mag-drive style pumps and 15%-25% heat transfer for other external pumps, especially if they are located in a closed stand!
