A licensed mechanical contractor is needed when an installation of new equipment is needed, but a repair can be done with no permit. Having a job permitted, allows the local city or county to send out their inspector to approve the work that was done. This insures that the new equipment was installed per manufacturers recommendations and per local guidelines. The homeowner can always ask for the permit number to ensure that the permit has been pulled. Once the installation has been finished, the inspector will then be scheduled. If the job is failed, then the contractor has to come back and make the appropriate adjustments.