Aquah Indoor Natural Gas Tankless Water Heater 16l / 4.3 Gpm, Whole House AQUAH natural gas tankless water heater, 4.23 gal (16 L)/min or 254gal/hr Automatic electrical pulse ignition with no standing pilot, operated by 2 D Batteries or 120V AC 85% thermal efficiency, 32,000 Watt / 109,260 Btu/h thermal input 45 dgrees temperature rise at the flow rate of 4.3 gllons per minute (GPM) Free 1/2" BSP (Metric) to 1/2" NPT adapters for gas/water fittings ($45 value).