insulation - How can I insulate my fireplace when it's not in use

I have a wood burning fireplace insert, that is not currently being used. Now that it's cold in my area (27F), I've noticed that there is quite a draft coming from the fireplace. How can I cover/

insulation - How can I insulate my fireplace when it's not in use? - Home Improvement Stack Exchange

Rockwool insulation vapor barrier inside chimney? - GreenBuildingAdvisor

Why Insulate a Chimney? : 4 Steps (with Pictures) - Instructables

Insulating a Decommissioned Chimney - GreenBuildingAdvisor

Electric Fireplace Insulation — An Ultimate Guide - Fireplace Inserts Guy

Insulation Near a Fireplace?

Installation series: 3/4 Insulation

Sealing A Drafty Fireplace, Adventures In DIY

Walls Behind Fireplaces Building America Solution Center

Gas fireplace draft ?

Insulate around brick fireplace - behind drywall

Gas Fireplace is Drafty, How Can I Reduce Outside Air from Coming Inside? : r/DIY