Mr. Heater Corporation F299721, Corporation, 20,000 BTU Vent Free Blue Flame Natural Gas Heater, MHVFB20NGT 20,000 BTU Natural Gas heater to heat spaces up to 500 square feet Blue flame burner for even convection heat. Thermostat for automatic temperature control Automatic low oxygen shut-off system (ODS). CSA Certified Operating this heater at altitudes over 4,500 FT above sea level could cause pilot/ODS to shutdown the heater. Theromostat, legs and wall mounting hardware included