Smoking undercover in the house.....
Hahahhhhhhaaaaaa
First things first, you need to make your room as air-tight as possible. Close vents, seal door cracks.
Next, you need to find a way to circulate the air in your room, away from the door and out an open window. 2-3 tabletop quiet tabletop fans will work for this. At least one by your door, and another right by your window pushing air out of the room. If the room's big you could always hit a "stagnant air" spot with a third fan blowing towards the window.
If you keep your smoking by the fan in the window, and make sure to exhale into the back of the fan so that it pushes all your exhaled smoke out immediately, you'll be able to smoke undercover for quite a long time, my brutha, provided your folks don't wonder why you're trying to create a tornado with fans in your room.