In general, it is not recommended to use the same duct for both exhaust fans in a kitchen, specifically the range hood and the dishwasher. These two appliances have different ventilation requirements and using a single duct for both can lead to several issues:
Airflow and Efficiency: Range hoods and dishwashers require different levels of airflow to function effectively. The range hood requires a larger duct and more airflow to efficiently remove cooking fumes, smoke, and odors from the kitchen. On the other hand, a dishwasher's exhaust needs are typically much lower. Using the same duct for both can result in inadequate ventilation for the range hood and reduced efficiency overall.
Grease and Contaminant Buildup: Cooking produces grease and other contaminants that are captured by the range hood filter. If the same duct is connected to the dishwasher exhaust, these contaminants can accumulate in the ductwork, leading to potential blockages and hygiene issues.
Odor and Moisture Transfer: The dishwasher exhaust contains moisture and odors from the dishwashing process. If this air is routed through the same duct as the range hood, it can cause unwanted smells and condensation issues, affecting both the dishwasher's performance and the range hood's effectiveness.
Compliance with Building Codes: In many places, building codes or regulations govern the proper installation of kitchen exhaust systems. Mixing the ducts for different appliances may violate these codes and could lead to safety or compliance issues.
To ensure both appliances function optimally and safely, it's best to have separate and dedicated ducts for each exhaust fan. If your kitchen layout or space constraints make it challenging to have separate ducts, consider consulting a professional HVAC or kitchen ventilation expert to find the best solution that complies with local building codes and meets the requirements of both the range hood and dishwasher.