If the design and free area of louvers are not known, what assumption is made regarding wood louvers' free area?

When the design and free area of wood louvers are not specified, it is accepted in the industry to assume that the free area is approximately 25% of the total area of the louvers. This assumption is based on empirical data and typical performance characteristics observed in wood louvers, which often feature obstructions due to their slats and frames. By estimating the free area at 25%, HVAC professionals ensure that sufficient airflow is accounted for in the system's design, allowing for proper ventilation and efficiency.

This assumption is crucial for accurately calculating airflow in various applications, minimizing the risk of underestimating the airflow capacity that could result in inadequate ventilation or inefficient system performance. The other percentages listed do not reflect the commonly accepted standard for wood louvers, which can lead to improper airflow calculations if used in their place.