Manufacturers of metal chimney liners, I.R.C. 2006 building codes, and Underwriters Laboratory UL 1777 Standards For Chimney Liners require all metal chimney liners to be insulated when solid fuel is burned in a chimney containing a metal chimney liner. When the preferred, poured-type of insulation is used, a 1” minimum thickness of poured insulation is required to completely surround the metal chimney liner. The chimney liner and poured insulation are two components that, together, create a safe, code compliant system that protects the dwelling from dangerous heat transfer that radiates from the chimney.
As illustration # 1 reflects, the metal chimney liner touches the inside surfaces of the chimney as the liner is being lowered into the chimney from the top. Wherever the metal chimney is in contact with the inside face of the chimney it is physically impossible to achieve the mandatory 1” minimum thickness of poured insulation. If the 1” thickness of poured insulation is not achieved, dangerous levels of heat transfer can occur from the chimney to the dwelling. Most homes are built with wood framing, joists, and trusses, which are exposed to the radiant heat. Through pyrolysis, the chemical decomposition of an organic material by heating, the ignition temperature of the surrounding wood gradually lowers. As the ignition temperature lowers, spontaneous combustion of the wood can occur.