Semi lost piece of historical technology that may be worth knowing about.

A Fireback is a simple steel or cast iron plate placed against the back wall of a fireplace. It serves a double purpose. It acts like a mirror for the heat of the fire in front of it, reflecting it out into the room before it can go up the chimney. Second it is a large thermal mass putting heat into the room long after the fire has burnt out.

Mine is a 1" thick 200lb piece of steel. Adding it doubled the comfortable sit in front of the fire distance for my fireplace. Since it is not my primary source of heat I do not get up to feed the fire overnight. The next morning hours after the fire is gone the fireback is typically around 200f and still warm enough to feel it when you walk past.