What does a system require in flow and pressure?

An NFPA 13D system is designed around one or two operating heads. Typical demand is 13 gallons per minute per sprinkler, and the design assumes two operate at once, so most applications generate a maximum flow of 26 to 35 gallons per minute. Required pressure depends on the sprinkler model and spacing; the NFPA 13D minimum is 7 psi at the head. Design duration is seven minutes for homes under 2,000 square feet and up to ten minutes for larger ones, which puts the total water needed for an event between 260 and 480 gallons. That is a domestic-scale demand, not a commercial one. Fire data from NFPA, NFSA, and Home Fire Sprinkler Coalition show that 94% of the time, 1-2 sprinklers control the fire – meaning the demand on the water supply is considerably less than the thousands of gallons fire departments need to control a house fire.