How far must the surface temperature of a UL-listed combustion appliance rise to prohibit the manufacturer from specifying it for a zero clearance to combustibles installation?

(I looked in UL 127 but was unable to find a straightforward answer there.)

  • $\begingroup$ Is this a UL controlled criteria or a building code controlled criteria? $\endgroup$
    – hazzey
    Commented Dec 10, 2015 at 1:36
  • $\begingroup$ @hazzey -- I'd expect it to be a UL thing as it'd be a criterion of listing the appliance and labeling/documenting it as zero clearance to combustibles safe, although it could be in the IMC somewhere... $\endgroup$ Commented Dec 10, 2015 at 2:05

2 Answers 2


I'd have posted this as a comment, but too much text. I found a doc online whose preamble listed all the following specifications as being related to zero-clearance design:

The following published specifications, standards, or tests that apply to flexible, fire rated grease dust wrap in this section:

A.  NFPA 96 (All Editions, including 2004, 2008, 2011), NFPA 101, 90A
B.  International Code Council Evaluation Service (ICCES)
C.  1997 ICBO Uniform Mechanical Code (ICBO UMC)
D.  1997 Uniform Building Code (UBC)
E.  2006, 2009 and 2012 International Mechanical Code (IMC) 
F.  2006 and 2009 IAPMO Uniform Mechanical Code (IAPMO UMC)
G.  2010 National Building Code of Canada
H.  ASTM E2336 Internal Fire Test, Zero Clearance to Combustibles, Grease Duct Enclosure
I.  CAN/ULC-S144-09 and -12 Standard Method of Fire Resistance Test – Grease Duct Assemblies.
J.  ASTM E-119 Engulfment Fire Test for 2 Hour Grease Duct Enclosure
K.  ASTM E-119 Fire Wall Test, 2 Hour Rating
L.  ASTM E-84 Standard Test Method for Surface Burning Characteristics of Building Materials
M.  ASTM E-814, UL/ULC 723 Standard Test Method for Fire Tests of Through-Penetration Fire Stops
N.  ASTM E-136 Standard Test Method for Noncombustibility
O.  ASTM E-518 Standard Test Method for Thermal Resistance (Durability)

An ad (PDF) for some ductwork quotes the following specs that their product meets: SETTING THE STANDARD…

ZeroClear™ meets the following stringent codes and standards:
• UL1978 – Standard for Grease Ducts – 2000° test
• UL2221 – Standard for Tests of Fire Resistive Grease
Duct Enclosure Assemblies
• ASTM E2336 – Standard Test Methods for Fire Resistive
Grease Duct Enclosure Systems – 1 hour (max) rating with ZeroClear
– 2 hour (max) rating with ZeroClear Plus
• NFPA96 – Standard for Ventilation Control and Fire Protection
of Commercial Cooking Operations
• International Mechanical Code

How one tracks down all those specs is another problem :-(


I finally found the answer to this in a BIA (Brick Industry Association) test protocol for standardized brick fireplace designs. To quote what they're saying about UL-127:

In general, after temperature equilibrium has been reached (or after 12 hours of fueling), UL-127 temperature limits on combustible surfaces are:

  • 90°F over ambient room temperature for unexposed (ie, in contact and covered) surfaces and

  • 117°F over ambient room temperature for surfaces exposed to ambient room air


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