i consider most specs to be optimistic . There are Takagi's rated at from 9.5 to 14.5 gpm with a 40 degree rise. A guesstimate calculation for an arch (Not waterfall sheet type) has Eight .05 nozles which works out to 4 gpm except the arches probably only run 2/3 of a minute at highest volume. so lets say 75% or 3 GPM useage. That means the small unit could handle 3 arches and the larger one could handle 5.