Why is smoke coming out of my exhaust pipe?

There are several things that can cause this.1.     The exhaust pipe must be hot to start the exhaust process.2.     Check that an exhaust pipe is properly connected and make sure that the rain cap is one of the open types, not one with small wire holes. They can become clogged with deposits and prevent proper venting.3.     Check if an exhaust pipe with rain cap is connected. The exhaust air must be open and must not be restricted. The exhaust pipe must not be installed with elbows.4.     The kitchen area must have a slightly positive air pressure. If the air pressure in the kitchen is negative, it can pull the smoke through the doors and / or the recirculating air outlet.5.     Make sure your supply / exhaust system is turned on. Also check the straps and filters. If the AC system of the building has an economizer, make sure that the outside air openings are open and ready for use.