Bosch AquaStar Natural Gas Tankless Water Heater #125HX-NG Provides 4.3-gallons of hot water per minute--enough for one application at a time Designed for vertical venting or for horizontal venting with optional AQ1 kit Unique hydro-generated ignition allows operation without standing pilot, electricity, or battery Cuts water-heating costs greenhouse gas emissions by up to 50 percent 29-3/4-by-18-1/4-by-8-3/4-inches; weighs 40-pounds