Our LP air mixture valve is what you will need whenever using LP for your indoor fireplace, outdoor fireplace or fire pit. LP or Liquid Propane is heavier than air and will burn dark and sooty if not mixed with air. Our LP air mixture valve, or air mixer, will mix air with the incoming LP to burn clean and bright. It’s more of a fitting than an actual valve and should be connected directly to your burner ring or pan. Make sure to install the fitting in the correct direction, the 150K and 300K burners have a flow directional arrow to follow. The 90K model only fits one way. The most common size is our 150K BTU model. If after installing one of our air mixture valves and you still see some sooting you may have moisture in your lines, excessive pressure, or an incorrectly sized gas orifice, please consult with a professional gas plumber.