105 CMR, § 410.201
The owner shall provide heat in every habitable room and every room containing a toilet, shower, or bathtub to at least 68°F (20° C) between 7:00 A.M. and 11:00 P.M. and at least 64°F (17° C) between 11:01 P.M. and 6:59 A.M. every day other than during the period from June 15th to September 15th, both inclusive, in each year except and to the extent the occupant is required to provide the fuel under a written letting agreement. The temperature shall at no time exceed 78°F (25° C) during the heating season. The temperature may be read and the requirement shall be met at a height of five feet above floor level on a wall any point more than five feet from the exterior wall. The number of days per year during which heat must be provided in accordance with 105 CMR 410.000 may be increased or decreased through a variance granted in accordance with the provisions of 105 CMR 410.840 notwithstanding the prohibitions of the first clause of the first sentence of 105 CMR 410.840(A).
105 CMR, § 410.201