Hot Water Heaters only weigh about 100 pounds and don't have a motor like many other appliances.
My new(used) water heater I just picked up from C.L. for the house has a blower on top for exhaust. I imagine their used a lot in newer homes so as they go bad we'll be seeing them with the electric blower motors.



Just a side note, there is big discussions about not putting a lot of wood/plastic/rocks in the steel pile. But when you take in an old wore out water heater your taking in an extra 25-50 lbs of rust and water.