Smoke enters the room at start up when it is cold outside and the bypass is open.

The venting that takes the exhaust outside is cold not allowing the smoke to go up. If you have a Greenstart igniter press the button before loading and let it, run a cycle. This will preheat the venting. If there is not an igniter on the insert, start a small hot fire at the rear of the firebox with newspaper. This will preheat the vent kick starting the draft.