How should recirculating direct-fired industrial air heaters receive outside ventilation air into the space?

The correct answer to the question emphasizes the importance of adhering to the specific requirements listed on the heater's rating plate. This is crucial because the rating plate contains information provided by the manufacturer that outlines the operational parameters and safety guidelines that are tailored to that specific heater model.

Following the requirements on the rating plate ensures that the heater operates efficiently and safely, taking into account its design, fuel type, and intended application. Each unit may have different ventilation needs based on its construction and specific operational characteristics.

While ventilation standards such as those from ASHRAE or local building codes are important, they serve as general guidelines and may not always account for the unique specifications of a particular heater. Therefore, relying on the manufacturer's instructions indicated on the rating plate is the best practice to ensure compliance and optimal performance.