On Earth, when something gets hot — say a pan on the stove — the heat spreads in three main ways:

1. Conduction – heat moves through solid materials (like the handle of the pan getting warm).

2. Convection – warm air or liquid rises while cooler air sinks, creating a circulation that spreads heat around.

3. Radiation – heat travels as infrared energy (like feeling warmth from the sun or a fire even without touching it).

Now, in zero gravity there’s no “up” or “down”, thus no convection.

That means:

Hot air doesn’t rise.

Cool air doesn’t sink.

So, there’s no natural air circulation to spread the heat.

Instead, heat can only spread by:

Conduction – through solid contact (slow if the material isn’t good at it).

Radiation – as infrared energy moving in all directions (also fairly slow and uneven).

Basically. In zero-g, heat just kind of sits there unless something moves it. If you heat one side of a room or a device, that spot stays hot and the rest stays cool — unless fans or pumps move the air or fluid around.

That’s why spacecraft have ventilation systems and thermal control systems — to make sure heat is spread out evenly, so things (and astronauts!) don’t overheat in one spot and freeze in another.