Bad practice to leave the firedoor open all the time, the cold air being drawn in is really bad for the boiler and stresses the sheets and the tubes. If it were modified like a full size British Engine and it had a flap for the firedoor, the deflector in the firebox above the firehole that extended underneath the brick arch, the secondary air coming in through the open door would mix properly with the volatiles and burn them efficiently in order to become hot enough to aid in steam production and not harm the boiler. It seemed she made steam more than well enough here but I don't know if it has an arch or not and in all likelihood it probably does not have the deflector.
Bad practice to leave the firedoor open all the time, the cold air being drawn in is really bad for the boiler and stresses the sheets and the tubes. If it were modified like a full size British Engine and it had a flap for the firedoor, the deflector in the firebox above the firehole that extended underneath the brick arch, the secondary air coming in through the open door would mix properly with the volatiles and burn them efficiently in order to become hot enough to aid in steam production and not harm the boiler. It seemed she made steam more than well enough here but I don't know if it has an arch or not and in all likelihood it probably does not have the deflector.