Why can smoke come into my room?

The quality of the wood: green or wet wood can cause more smoke than the fireplace can evacuate.
Air systems such as air conditioning, kitchen or bathroom fans can take in the air required by the fireplace (negative air circulation).
Misuse: Always open the primary air control before recharging the heater and slowly open the door.
The tubes of the stove and chimney: do not forget that (90º) elbows and long horizontal tubes reduce the air circulation.
Too short a chimney which does not provide enough air circulation in the fire chamber.
A cold chimney can prevent air circulation (negative air).
A pipe liner must be properly connected to the chimney and the correct size.