CO2 (carbon dioxide) is needed by plants for proper growth. CO2 can be added by burning propane or natural gas - cheaper and easier to obtain than bottled CO2. The Gas Pro uses faster, more reliable, more efficient, electronic spark ignition. When the Gas Pro is turned on, spark and pilot gas start. When the pilot is lit, spark stops and main gas turns on and is lit by pilot. When the Gas Pro turns off, all gas turns off. Spark is better than standing/continuous pilot because they must be manually lit, burn all the time, and waste gas. Spark is faster and more reliable than a glow plug - no time needed for glow plug to heat up, spark ignites immediately. Both Propane and Natural Gas models available. Each have two sizes - a six burner and a twelve burner. The Propane model includes a regulator for connection to a propane tank. Gas hose (20 ft.) included with all models. Strong 18 gage steel enclosure - powder coated for heat and rust resistance. Heat exchanger allows forced air cooling if desired. Plug the 120V power supply (included) into a controller or timer. Alternatively, the Gas Pro allows easy connection of a CO2-400 controller. Just plug CO2-400 's 10 ft. cable into connector on the side of Gas Pro. Extension cable available. No separate power supply needed - it draws power from the Gas Pro. The CO2-400 has a display and buttons for showing present PPM and setting desired PPM level.