Should the purifier be installed before or after the fan?

Most designs place the purifier on the fan inlet side so the fan handles relatively clean air; the exact position depends on ducting, fire dampers, maintenance access and manufacturer design. Leave enough surrounding space for removal, cleaning and servicing. Checklist: Define capacity, accuracy, materials and operating environment before requesting quotes on a uniform basis. Request specification sheets, test reports, certificates, maintenance manuals and spare-part lists. During acceptance, verify appearance, dimensions, functions, safety protection and packaging, and keep test records. Do not compare unit price alone; include customization, freight, spare parts, after-sales support and downtime risk. Keep written records of inquiries, confirmations, FAT, acceptance and warranty commitments.