Whats wrong with traditional dampers?
Traditional construction of brick or stone fireplaces includes a “throat damper” just above the firebox. This is an iron or steel frame with a plate that opens by pushing a handle or turning a knob. You might think of it as the lid of a cast-iron pot, in the sense that it closes, but not tightly. Some fireplaces have no damper at all. The chimney is designed to draw warm air up and out. If you close a throat damper when you’re not using the fireplace you’ll cut heat loss, but you’ll still lose a lot of heat. After all, it’s just a rough-cast metal plate resting over the opening. There’s no seal. Around this loose-fitting closure, the chimney draws warm air up and out all winter long.
