Mr. Heater, Corporation, 20,000 BTU Vent Free Radiant Natural Gas Heater, MHVFRD20NGT 20,000 BTU Natural Gas heater to heat spaces up to 500 sqaure feet. Radiant heat burner 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. Refer to the PDF attached below in Technical Specification for User Manual.