What is the minimum flame rating for plenums?

What is the minimum flame rating for plenums?

• A. 15
• B. 25
• C. 20
• D. 30

Answer: (B)

In HVAC plenums, the materials used must resist flame spread so fire and smoke don’t race through the air-handling paths. The flame spread rating indicates how quickly flames can travel along a surface, and codes set a limit for plenums: the rating must not exceed 25. That means any material with a flame spread of 25 or less is acceptable for plenums. So the standard threshold you’re expected to meet is 25. A rating higher than that, like 30, would not meet the requirement, while ratings lower than 25 (such as 15 or 20) would be more restrictive than necessary but technically would comply with the limit.

In HVAC plenums, the materials used must resist flame spread so fire and smoke don’t race through the air-handling paths. The flame spread rating indicates how quickly flames can travel along a surface, and codes set a limit for plenums: the rating must not exceed 25. That means any material with a flame spread of 25 or less is acceptable for plenums. So the standard threshold you’re expected to meet is 25. A rating higher than that, like 30, would not meet the requirement, while ratings lower than 25 (such as 15 or 20) would be more restrictive than necessary but technically would comply with the limit.