Damper valves in flues and chimneys

2116. Dampers, or valves, are useful in flues and chimneys, both in case of accident and also to moderate the heat, or, in case of one furnace supplying two flues, to regulate the passage of smoke and heat. For general purposes, however, the ash-pit door is perfectly suflicient. The damper, and furnace, and ash-pit doors ought seldom to be all shut at the same time, as such a confinement of the hot air of the flue is apt, owing to its expansion by increased heat from the hot masonry, to force some of it through the joints of the flue into the house.