The first step that a technician or furnace owner should follow while replacing an old furnace is to switch off the main power.  If a breaker supplies main power to the furnace, flip it off before replacing the furnace to avoid electric shocks.  Furnace owners should let professional technicians from HVAC companies providing heating replacement in Anaheim, CA, do this job as it has many technicalities and wiring work.  Those replacing the furnace can wear latex or rubber gloves to avoid electric shocks.