I am facing my first winter of brewing with a swamp cooler. I need to acquire a few aquarium heaters (incidentally, please let me know if you know a good brand) and drop them in my swamp cooler to maintain temperature.
Now almost everything I read online states that I also need to acquire a water pump to place underneath the water heater in order to "distribute the hot water into the colder parts of the water" ...
Why am I to believe that this is necessary? What force of nature could possibly prevent warm water from being evenly and automatically distributed over 5-7 gallons of water in a swamp cooler?
The general internet consensus is that only a few inches of water around the water heater will remain warm, that the warmth somehow stays in the same spot, that it doesn't distribute itself as physics as I understand it would require it.
Why is the pump required -- what is the scientific explanation for how it is possible that warmth wouldn't flow from a hotter area to a colder area without the assistance from a pump, contrary to my understanding?