How does a fireplace work?

Once a fire is lit in the fireplace, the gas and air released through the flames flows out the chimney, which in turn pulls oxygen into the fire from the house to keep it burning and producing heat. A fireplace depends on airflow.

If a fireplace does not get sufficient airflow, then numerous things can happen, some of which can be very dangerous. The most harmless thing that can happen is the fire will die, while more severe reactions include the possibility of smoke filling the house, which in turn could cause carbon monoxide poisoning if it is not caught in time.