Each facility should provide heating for every cell, bathroom and toilet compartment, and other habitable area, at a temperature of at least 68°F, between 7:00 A.M. and 11:00 P.M, and at least 64°F, between 11:01 P.M. and 6:59 A.M., every day other than during the period from June 15th to September 15th, inclusive, in each year. The temperature should at no time exceed 78°F during the heating season. For each degree below 15° below 0°F that the temperature falls, the minimum temperature requirement may likewise be reduced by 1°F. The temperature is read at a height of three feet above floor level at any point in the room more than two feet from the inside of every exterior wall.
105 CMR, § 451.330