A thermal regulator could refer to an engineering tool, or a component of a starship's or planet's environmental control system.

The climate on the planet Caldos was controlled by several thermal regulators. When it started to rain unexpectedly in the middle of summer, the maintenance crew checked the thermal regulators and climatic flow array for a malfunction. (TNG: "Sub Rosa")

During the USS Voyager's maintenance overhaul in 2377, Lieutenant B'Elanna Torres reported that the thermal regulators were "still running a little hot." (VOY: "Nightingale")

Later that year, Captain Kathryn Janeway used a thermal regulator in an attempt to repair the replicator in her quarters. (VOY: "Shattered")