At the time, mid 1970's, an economical install of electric heat was a resistive cable system, installed on rock lath ceilings before plaster was applied. (There was a similar install using a double layer of 3/8" drywall for ceiling). A similar stapler was used. Did two houses with this system. Each cable was sized per room, there was no cutting. Cable was closer together exterior walls. Line T-stat (240 volts) was installed on an inside wall. Bostich T5. still works.