(a) On and after February 1, 1952, where an apartment, in whole or in part, is rented or sought to be rented to more than one tenant, the landlord shall file an application with the administrator to fix maximum rents for the units or portions of such apartment. Such application shall set forth the present maximum rent for the apartment, the furniture, furnishings, facilities, equipment and other services added or proposed to be added, the number of occupants and the space to be occupied by each tenant in such apartment, the terms and conditions of occupancy, and all other data which may be required by the administrator. In fixing the maximum rent, the administrator shall apportion the previous maximum rent for the entire apartment among the tenants in proportion to the space they occupy, and shall add thereto the increased rental value of any furniture, furnishings, facilities and equipment added by the landlord. Where the landlord has satisfied all of the requirements of the authorities having jurisdiction over the physical conversion and over the occupancy of the changed housing accommodations, the administrator, in fixing maximum rents for individual tenants, shall also take into consideration all factors bearing on the equities involved, including the cost of any physical conversion or alteration. If there was no previous maximum rent for the entire apartment, the administrator, prior to making the apportionment and fixing a maximum rent for each tenant as hereinabove required, shall establish a maximum rent for the entire apartment, having regard for the maximum rents for comparable housing accommodations, or any factors bearing on the equities involved, consistent with the purposes of the Rent Law. Unless and until an order is issued by the administrator fixing maximum rents for the individual tenants of the apartment, the aggregate maximum rent for all of the tenants in the apartment shall be the maximum rent previously established for the apartment. All orders issued under this section shall be effective as of the date of first renting.

(b) Where no application has been made under this section, the administrator at any time, upon written request of a tenant or on his own initiative, may issue an order pursuant to this section fixing or establishing a maximum rent for each of the individual tenants in the apartment, effective as of the date of such renting. In fixing such maximum rents for the individual tenants, the administrator shall use the standards prescribed in subdivision (a) of this section. Such order may contain a directive that all rent collected in excess of the maximum rent established under this subdivision, during the period beginning no earlier than two years prior to the date of the filing of the tenant's statement of violations, if any, or the date of the commencement of the proceeding to fix or establish the maximum rent, whichever date is earlier, shall be refunded to the tenant, together with six percent interest from the date of each such excessive payment of rent, within 30 days after such order shall become final.