Can a clothes dryer be common vented with a water heater provided the vent capacity is adequate?

The correct understanding is that a clothes dryer should not be common vented with a water heater, regardless of the adequacy of vent capacity. This is due to safety and performance standards established in various building codes and manufacturers' guidelines.

Clothes dryers and water heaters operate on different principles; dryers expel moist air, while water heaters vent combustion gases. Mixing these two systems could lead to issues such as backdrafting, where harmful gases from the water heater could enter the dryer and subsequently the living space, creating safety hazards. Additionally, it could hinder the proper function of both appliances, leading to inefficiency and potential damage.

While there may be some scenarios where people might think about venting them together based on capacity, regulations on venting prioritize safety and ensure that appliances operate under optimal conditions. Therefore, the appropriate conclusion is that common venting between a clothes dryer and a water heater is not permissible.