20 CFR § 654.409 - Heating.

(a) All living quarters and service rooms must be provided with properly installed, operable heating equipment capable of maintaining a temperature of at least 68 degrees Fahrenheit ( °F) if during the period of normal occupancy the temperature in such quarters falls below 68 °F.

(b) Any stoves or other sources of heat utilizing combustible fuel must be installed and vented in such a manner as to prevent fire hazards and a dangerous concentration of gases. No portable heaters other than those operated by electricity may be provided. If a solid or liquid fuel stove is used in a room with wooden or other combustible flooring, there must be a concrete slab, insulated metal sheet, or other fireproof material on the floor under each stove, extending at least 18 inches beyond the perimeter of the base of the stove.

(c) Any wall or ceiling within 18 inches of a solid or liquid fuel stove or a stovepipe must be of fireproof material. A vented metal collar must be installed around a stovepipe, or vent passing through a wall, ceiling, floor, or roof.

(d) When a heating system has automatic controls, the controls must be of the type which cut off the fuel supply upon the failure or interruption of the flame or ignition, or whenever a predetermined safe temperature or pressure is exceeded.