Return-side smoke detection threshold under NFPA 90A applies to systems that serve more than one story and have capacity of

Return-side smoke detection threshold under NFPA 90A applies to systems that serve more than one story and have capacity of

• A. 2000 CFM
• B. 15000 CFM
• C. 1000 CFM
• D. 10000 CFM

Answer: (B)

Return-side smoke detection is used to catch smoke in the return air stream of large central HVAC systems that serve more than one story. The idea is that when a system moves a lot of air, smoke can travel quickly through the return ducts and spread to other areas. NFPA 90A specifies that this protection is required for multi-story systems when the airflow capacity is high enough to pose a rapid dissemination risk. The threshold is 15000 CFM, so systems meeting or exceeding that capacity must have return-side smoke detection. The other capacity options are below this threshold and do not meet the NFPA 90A requirement, which is why the correct choice is 15000 CFM.

Return-side smoke detection is used to catch smoke in the return air stream of large central HVAC systems that serve more than one story. The idea is that when a system moves a lot of air, smoke can travel quickly through the return ducts and spread to other areas. NFPA 90A specifies that this protection is required for multi-story systems when the airflow capacity is high enough to pose a rapid dissemination risk. The threshold is 15000 CFM, so systems meeting or exceeding that capacity must have return-side smoke detection. The other capacity options are below this threshold and do not meet the NFPA 90A requirement, which is why the correct choice is 15000 CFM.