Fireplace Manual Mark 123-38C

Confirming the Hearth or Hearth Extension

Most fireplace inserts need 18” of non-combustible material on the floor (hearth) in front of the door opening. In some cases, this hearth (and the existing hearth) must also meet certain R or K insulation values. These values are specified in the owners manual and are required to avoid overheating of the combustible materials underneath the hearth. Note that many stove manuals will show 16” as the hearth extension (in front), while the newest NFPA codes require 18”. The manuals have not yet caught up to the code - so use the 18” whenever possible. Read some of our other articles on hearth clearances and construction for tips on building or buying an extension.