How do I insulate below a fireplace?

Is It Safe to Put Insulation Behind a Gas Fireplace?

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

How to Seal an Unused Fireplace and Save Money on Heating Bills - Dengarden

Insulation in the surround? : r/Fireplaces

Code Requirements for Fireplace Clearances - Fine Homebuilding

Sealing a Chimney Chase

Running power and conduit above fireplace

How do I insulate below a fireplace? AnandTech Forums: Technology, Hardware, Software, and Deals

Will A Fireplace Heat Basements? - We Love Fire

How to Insulate a Fireplace and Chimney to Improve Efficiency

Chimney insulation best practices guide - e-architect