Does heat diffuse/equilibrium in water?

[Miami Reef]

I have a 40 gallon brute with uncirculated water. If I add a 40 gallon rated heater to the bottom of the container, will the heat diffuse into the whole container until it reaches the temperature.

OR. Will the heat stay in the same area, thus causing the heater to shut off as the surrounding water is warm, but the water towards the top of the container still cold?

 

[Dcal]

Warm water rises and cold water sinks so I would assume using that property you would get some sort of a mix cycle going if the heater was on the bottom.

Either way id just pick up a 5$ powerhead on amazon unless its not an option

 

[lynaea75]

My vote would be yes and no, the hot water will rise but in that volume and height of water it would probably take a long time to equalize and would depend on room temp too.
I second the vote for a cheap pump.

 

[Randy Holmes-Farley Verified Community Expert]

Convection currents (water flow driven by density differences) will keep it relatively well mixed in temperature. Is it important that it stay exactly even temperature everywhere if it is just for storage?

 

[Miami Reef]

Convection currents (water flow driven by density differences) will keep it relatively well mixed in temperature. Is it important that it stay exactly even temperature everywhere if it is just for storage?

It doesn’t have to be perfect. I like to heat the brute can up right before a water change for my QT. As long as it’s in a range I’m fine.

 

[Malcontent]

I found that given the same heaters/wattage, heating of a barrel of water is much faster when there's water movement so I always have a pump going until it reaches target temperature. Then I unplug the pump and all but one heater and that maintains the temperature.

 

[legionofdoon]

When I used to house cichlids I could see the warm water rising up from the heater in the tank and then mixing with the rest of the water. Just like air, convection transfers heat typically upwards in water, except when ice forms at which point water expands (unlike most other materials that go from liquid to solid) and becomes less dense so ice floats but it then acts as an insulator keeping the remaining heat in the liquid allowing life on earth to exist.

tl;dr : no you don't need a pump, convection transfers heat throughout, but a pump will speed up the process, however what uses more watts in the long run is up to you.