AskCodeMan

Do the manufacturer's installation intructions regarding clearances on a metal chimney with UL 103 approval make allowances for or provide for the system to withstand a chimney fire? Is this what the high temp. section of the test is for? I'm not having any luck getting info. out of UL and can't afford $500 to buy the code at the moment just to answer this question.
Thanks,
Len W.

The UL 103 listing sets conditions that supposedly reflect both normal continued use and the extreme conditions of worst case. For solid fuel, that would include the optional HT or High Temperature test. A std. 103 chimney is rated to 1,700F max and 1,000F continuous. The HT test includes three 10 minute 2,100F tests to simulate a chimney fire condition. The test structure is 3/4" plywood painted flat black with thermocouples every 6" in a grid. The mfr. tells the test agency at what clearance to test so that is the box they build. All the seams are taped then the unit fired. If any one thermocouple rises more than 90F above the ambient room temp., the chimney fails. If it fails, you build the box bigger until it passes and that is how they arrive at the stated clearances. Also, the pipe is inspected for damage, separation, or loss of joint integrity. There are numerous other tests on the strength and so forth but that's the main issue.
HTH,
Hearthman