Hello, looking for clarification on whether duct detectors are required on existing heat pumps which are individually rated at less than 2000 cfm, but multiple utilize the same plenum return. Area smoke detectors are not provided. My understanding is NFPA 90A requires duct detectors on 'air supply systems' over 2000 cfm. My question is do the individual heat pumps require duct detection since none of them are delivering 2000 cfm or greater? The building is a B Occupancy. Thanks in advance.