Freshwater Tim;3379953; said:
"Just my cent & 3/4ths..." lol
A 20 Watt powerhead would create FAR less heat than a 20 W heater. The heater is designed to use all of the energy to create heat... the powerhead is designed to use all of it's energy to create motion with only a small amount of heat being create due to imperfect mechanics...
As for oxygenation... Essentially, you need two things...
1. Surface agitation... this is any disturbance of the surface. It does not need to be water splashing upwards, any form of movement will do. Bubbles breaking at the surface works well... HOBs returning into the surface work well... A canister or powerhead making waves works just as fine...
2. Proper water circulation... Water at the surface becomes oxygenated, but you need your water column in general to be constantly diluting itself with itself to move that oxygen from the surface to spread throughout the tank.
This is ultra simple to achieve and standard forms of filtration typically serve this function just fine. If, your fish appear to be starving for oxygen (most commonly noted by seeing them nipping at the surface) Then you likely suffer from not enough water movement in general, which leads to a whole list of problems...
The bubbles themselves do not add enough oxygen to the water to both factoring in. They do provide miniature "surface to air interfaces" increasing the overall "surface area" of an aquarium... but I invite any of you to calculate the approximate surface area of the amount of bubbles produced by a bubbler that are in the tank at any one given moment... and compare that value to the surface area of the water's surface (factor in the increase due to agitation

)