This gas-fired water heater is equipped with eco-friendly burners (LOW NOx) for effective, pollution-free combustion. FVIR technology prevents the ignition of flammable vapours (including aerosols, solvents, gasoline, paint, paint thinner and lacquer) outside of the water heater. This water heater require a chimney. Additional information Water heater Gas-Fired – Atmospheric Vent Model UG40-ATM Type of gas Natural Storage Capacity (U.S. Gal.) 40 Storage Capacity (Litres) 151 Storage Capacity (Imp. Gal.) 33 Input BTUs (Natural gas) 38,000GI-PB-Residential-Gas-Fired-Atmospheric-Vent.pdfGI-FT-Res-UG40-ATM-En.pdf