Sous-vide without a pump using convection?
I made a sous-vide setup that uses a slow cooker and no pump. 

I was able to observe as much as a 5 degree temperature gradient from the bottom to the top of the cooker. A big part of the problem was that my target food almost fills the cooker and impedes convection. I didn't measure the temperature gradient with an empty bath.

My setup worked passably well as long as my food was small and my thermometer was positioned at the same depth. I didn't enjoy the precision that commercial products have.

Obviously your setup will have a lot more power than mine. If your bath is much bigger than your target food you would have less of a temperature gradient than I did.
If your bath is much larger than your target food then convection will give you enough water circulation. Even a 5 degree drift will let you do some interesting things, however, It is one more variable to keep track of.

I was not satisfied with my setup and my next attempt will have a stronger heater as well as a circulation pump. Water pumps are cheap.