Bathroom exhaust fan installation: electrical and duct work

Bathroom exhaust fan installation is two coordinated scopes: ventilation and electrical work. Ask for the fan model and tested airflow, duct diameter and route, exterior termination, switch or timer, ceiling access, and finish restoration. A quote that lists only the fan and an electrical connection may leave the moisture-control work incomplete.

ENERGY STAR’s ventilation-fan criteria require certified bathroom fans to deliver tested airflow at a defined static pressure, which makes the model’s performance more meaningful than a marketing CFM label alone (ENERGY STAR ventilation-fan criteria). The Department of Energy’s recessed-light air-sealing job aid identifies exhaust fans and ceiling penetrations as locations that need sealing in relevant retrofit work (DOE weatherization job aid). These sources support performance and air-sealing questions; they do not set local labor rates or a universal duct design.

Separate the quote into four parts

1. Fan and control: Model, airflow, noise rating if relevant, light or heater options, timer or humidity control, and whether the existing switch box supports the control.
2. Duct path: Length, bends, insulation, support, termination cap, and whether the duct exits through a wall or roof. A short attic route and a roof penetration are different scopes.
3. Electrical work: Existing circuit and box condition, new cable if needed, GFCI or other protection required by the authority, and any smart-control neutral requirement.
4. Access and finish: Ceiling opening, joist or truss conflicts, attic insulation handling, air sealing, drywall or plaster patching, texture, paint, and exterior flashing.

The contractor should explain where the fan discharges. Recirculating a bathroom fan into an attic or wall cavity defeats the moisture-control purpose and can create a building-envelope problem. Ask for the termination location and weatherproofing detail in writing.

What “replacement” really means

If the new fan fits the existing opening and duct, the work may be relatively contained. A larger housing, a new location, inaccessible junction box, or a damaged duct can turn replacement into a retrofit. Confirm whether the quote includes removing the old fan, hauling it away, and making the ceiling opening look finished.

Do not select a fan from the airflow number alone. Compare the model’s tested criteria, duct requirements, sound, controls, and service access. Give bidders the ceiling height, attic access, exterior wall or roof information, and a photo of the existing control. A qualified electrician should handle line-voltage connections; duct and finish work should be assigned clearly so the final price reflects the complete job.

Ask for the duct material and termination type, not only its diameter. A short, smooth route with few bends is easier to inspect and clean than a long flexible run. A roof termination can require a roofer or flashing detail; a wall termination may need siding or masonry repair. Identify that trade handoff before work begins.

The control also affects value. A simple switch, countdown timer, humidity sensor, light, and heater each require a different wiring and box plan. Ask who supplies the control and whether the electrician verifies that the fan starts, runs, and shuts off as programmed. Keep the model and duct route in the home records for future cleaning or replacement.