Mounting a powered bathroom ventilation fan inside a cold air return is not recommended and can be potentially dangerous. Cold air returns are part of the heating, ventilation, and air conditioning (HVAC) system, and their primary function is to draw cold air from the living space back to the furnace or air handler to be heated. Here's why it's not advisable:
Airflow disruption: Placing a bathroom ventilation fan inside the cold air return can disrupt the airflow within the HVAC system. The bathroom fan may not be designed to handle the volume of air that passes through the return duct, leading to imbalances in the system's air distribution.
Potential damage to the fan: Bathroom ventilation fans are typically designed to expel moist air from the bathroom to the outdoors or into the attic space. Mounting the fan inside the cold air return could expose it to higher humidity levels, which could lead to premature wear and damage.
Safety concerns: Mixing bathroom exhaust air with the return air can introduce moisture, odors, and potential contaminants into the HVAC system, which may circulate throughout the house. This could lead to indoor air quality issues and potentially impact the health of occupants.
Building code violations: Modifying the HVAC system without following local building codes and regulations can result in non-compliance and may affect your home's insurance coverage.
If you need to improve bathroom ventilation or address issues with humidity and odors, it's best to install a dedicated bathroom ventilation fan that exhausts directly to the outdoors or into the attic. This way, you can ensure proper airflow, prevent potential damage to the fan, and maintain good indoor air quality.
If you're uncertain about making modifications to your HVAC system or installing a bathroom ventilation fan, it's always best to consult with a qualified HVAC professional or electrician who can assess your specific situation and recommend appropriate solutions. They can ensure that any modifications or installations are done safely and in compliance with local building codes.