Dyna-Glo BF20NMDG 20,000 BTU Natural Gas Blue Flame Vent Free Wall Heater Natural Gas Ready (Fuel conversion not permitted) Blue Flame Technology works by convecting heat to warm the air the same way as a central heating system Up to 20,000 BTU's/hr heats up to 700 sq. ft.Separately sold optional base legs (WBL100) allows for stable floor mounting Separately sold optional fan (WHF100) improves the amount of square footage the heat reaches in a quiet, yet powerful way.No electricity required allows for reliable back-up heating incase of an emergency situation Manual LOW-MED-HI variable control knob offers the most customizable heat settings.1 Year Warranty