A thermal heater was a device designed to produce warming temperatures for individuals who were in environments which were prohibitively cold.

In 2266, the crew of the Enterprise attempted to beam down thermal heaters to Lieutenant Sulu and his away team when they were stranded on the surface of planet Alfa 177, where the temperature was dropping drastically. Due to the malfunction of the ship's transporter, which prevented the away team's transport up from the surface in the first place, however, the heaters duplicated and would not function. (TOS: "The Enemy Within")