Why Does a Heater in a Swamp Cooler Require a Pump to Distribute the Heated Liquid?

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?

Topic swamp-cooler temperature-control temperature homebrew

Category Mac

1
answered at

The aquarium heaters are not heating all of the water, but only the water around each heater.

This will form convection currents around each heater - the heated water only moves upwards, and rises up to the surface, at the same time water at the surface cools and sinks. The convection currents are probably only a few inches around each heater, depending upon the power of the heater. Water that is not in the convection is essentially unheated.

This means water between the heaters does not heat up much, and the water below the heaters will not heat up much either - the heated water does not move downwards or sideways.

When left alone, you'll get stratification in the water - low temp water at the bottom, and higher temp water at the top. By using a pump, you ensure the water is mixed, and that the heat is more evenly distributed throughout the body of water.

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