When HVAC work needs a permit in Frisco, Plano, McKinney, Allen and The Colony

• Replacing the outdoor unit, the indoor coil, the furnace or the air handler, together or separately
• Adding a system, moving a system, or changing from gas to a heat pump
• Significant duct replacement in some cities; ask
• Not required: repairs of any kind, tune-ups, capacitors, contactors, motors, control boards, thermostats, drain line work, refrigerant repairs

The installing contractor, who must be registered with the city doing the work. Frisco, Plano, McKinney, Allen and The Colony each run their own building department and their own online portal. The contractor applies, pays the fee (typically under a couple hundred dollars, varying by city and by the job), does the work, and schedules the inspection. The permit is tied to your address and becomes part of the public record for the house.

• The equipment matches the permit and is a matched, legal-efficiency system
• The disconnect and the electrical are correct for the new unit
• The condensate drain is trapped, pitched and protected: a float switch or a secondary pan with its own drain in the attic
• Gas connections, venting and combustion air on a furnace
• Line set routing, support and insulation
• Clearances and the equipment platform in the attic

Three reasons. The inspection is an independent check on work you cannot see in the attic, and it is the one time someone other than the installer looks at the drain protection that saves ceilings. An unpermitted replacement surfaces at resale, when the buyer's inspector notes a new system and the city has no record, and the fix can be opening walls or paying for a retroactive permit and inspection on the seller's schedule. And insurance claims for water or fire damage from HVAC equipment go better when the install was inspected.

Call the city's building department, explain, and ask about a permit after the fact. Most cities allow it with an inspection, sometimes at a higher fee. The installing contractor should do this at their expense; if they are gone, a licensed contractor can apply on the existing equipment.