What is the design friction rate for a static pressure of 0.36" WC and a run of 375?

To determine the design friction rate, one must know the static pressure and the length of the duct run. In a typical HVAC system, the design friction rate calculations often adhere to specific formulas that are influenced by code guidelines and practical applications.

In this case, with a static pressure of 0.36 inches of water column (WC) and a duct run of 375 feet, industry standards can be applied. Commonly, designers simplify the process by considering a friction rate that would allow for a manageable airflow drop across the run. The most utilized rates in standard practices for residential or light commercial applications usually range between values like 0.10" WC to 0.20" WC per 100 feet of duct length.

Given the stated pressure loss across the total run, a friction rate of 0.10" WC is plausible as it aligns with typical calculations and friction loss charts that assess such scenarios. This rate enables effective airflow while balancing the pressure drop incurred by the duct system. Additionally, calculating friction loss directly relates the static pressure loss observed over the duct proportional to its length, providing airflow efficiency without excessive pressure loss that could hinder performance.

Thus, the correct choice reflects common practice and successful design outcomes in HVAC ductwork planning, ensuring