Glass is breakable. • Avoid striking, scratching or slamming glass • Avoid abrasive cleaners • Do not clean glass while it is hot E. Firebrick Inspection • Frequency: After each ash removal • By: Homeowner Replace the firebrick if they become, cracked, broken, crumbly and/or if there is a 1/4 inch (6.35mm) gap between the bricks. The firebox is lined with high quality firebrick, which has exceptional insulating properties. There is no need to use a grate; simply build a fire on the firebox floor