Fireplace roast loss? Wondering if anyone has any thinking on how I can prevent heat...

Wondering if anyone has any thinking on how I can prevent heat loss from my masonary fireplace. Want to still use it surrounded by winter, just save heat from going up it when not contained by use. So stuffing insulation up by the damper would sure be a drag.......Any great ideas or links would surely be appreciated.......thankfulness
Answers:    paint a decorative scene on a piece of plywood near a styrofoam backing that fits your first showing when you arent using the fireplace...when you use it , glass doors...
gte a fireplace insert or chalice doors