a) No public electric or gas utility, after the effective date of this Part, shall be required to file with the Commission a schedule of any variation in any promotional practice or allowance filed pursuant to Section 275.50 (a) hereof, unless as a result of such variation:

1. 1) Any promotional practice or allowance provided for in cash, property or its equivalent in said variation, with respect to any residential dwelling unit for space heating, air conditioning, or any combination of space heating, air conditioning, wiring or piping, range, dryer or any other household appliance, is increased to more than 15¢ per square foot.
2. 2) Any promotional practice or allowance in cash, property or its equivalent, with respect to the purchase or installation of a range in any dwelling unit, is increased to more than $35 or to more than $20 for a dryer or any other household appliance; provided, however, that no such variation in practice or allowance shall be deemed a qualified promotional practice or allowance unless the cost of such practice or allowance can be recovered from the additional revenue obtained, less the incremental cost of supplying the additional electricity or gas, in a period of time not in excess of 50% of the estimated life of the space heating, air conditioning or appliance being promoted.