§ 84. Complaints as to service and price of steam heat; investigation by commission; forms of complaints. Upon the complaint in writing of the mayor of the city, the trustees of a village or the town board of a town in which a person or corporation is authorized to manufacture, sell or supply steam for heat or power, or upon the complaint in writing of not less than fifty customers or purchasers of such steam heat in cities of the first or second class, or of not less than twenty-five in cities of the third class, or of not less than ten elsewhere, or upon the complaint in writing of the department of state, as to the price, pressure or efficiency of steam supplied for heat or power, sold and delivered in such municipality, the commission shall investigate as to the cause for such complaint. When such complaint is made, the commission may, by its agents, examiners and inspectors, inspect the work, system, plant, devices, appliances and methods used by such person or corporation in manufacturing, transmitting and supplying such steam, and may examine or cause to be examined the books and papers of such person or corporation pertaining to the manufacture, sale, transmitting and supplying of such steam. The form and contents of complaints made as provided in this section shall be prescribed by the commission. Such complaint shall be signed by the officers, or by the customers, purchasers or subscribers making them, who must add to their signatures their place of residence, by street and number, if any.