American Standard Water Heaters High Efficiency Ultra-Low NOx commercial gas-fired water heater provides up to 250K Btu input with 97% thermal efficiency. The unit operates on natural and LP gas and includes electronic controls for ignition and temperature, zero-inch clearance and a full-size hand-hole cleanout port. It is available in 70 and 100-gallon capacities and is Energy Star- and AHRI-certified.