For our luxury line, we have the 931 series which can provide endless hot water for up to 4+ showers at a time.And with its Quick-Connect system, two units can be linked together to meet the high demand of today's luxury homes.To accommodate the higher flow rate demand, these units have a dual flame burner, a redesigned heat exchanger and 25% thicker copper piping.No other tankless water heater in its class can beat its performance, dependability, and quality. The N-0931M is for indoor/outdoor use. The N-0931M-DV is for indoor use only.ss The N-0931M-OD is for outdoor use only.