Question: I just moved into a house with a fireplace that has a heatolator (with fans) and glass doors. What is the best way to operate this fireplace? Should I keep the glass doors closed to keep warm air from going up the chimney? Answer: Both...When the fire is burning well, the doors should be open, which allows the radiant heat from the fire to warm you. When the fire is low, then close the doors. This will stop excess house air, which you already paid to heat, from going up the chimney.