What is manual S for HVAC is ACCA standard for residential equipment selection that uses Manual J load calculation results to choose correctly sized heating and cooling equipment. Manual S ensures selected furnace, air conditioner, or heat pump has appropriate capacity to meet heating and cooling loads at design conditions without excessive oversizing. Procedure: take total heating load and total cooling load with sensible and latent breakdown from Manual J, then compare to manufacturer expanded performance data for equipment at actual design temperatures, not just nominal ratings. Manual S sets allowable oversizing limits: air conditioner 95 to 115 percent of total cooling load and 90 to 115 percent of sensible load, heat pump 90 to 120 percent of cooling load, furnace 100 to 140 percent of heating load. It also verifies airflow CFM matches duct system, checks sensible heat ratio, and ensures heating capacity adequate. Without Manual S, contractor might select wrong size even with correct Manual J. Building codes require Manual S along with Manual J and D for permit. So Manual S is equipment selection protocol.
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