Testing Steps of UL Subject 2425

Summary of Test Findings
Go straight to the overall test findings and skip the individual testing steps to see how HeatShield® performed in the UL Subject 2425 Outline of Investigation
Construction of Test Chimney (Step 1)
A test chimney is constructed in the lab.
HeatShield® Cerfractory® Application (Step 2)
HeatShield® is applied to the walls of the flue tile liner.
Flue Gas Temperature Tests 1000°F, 1400°F, 2100°F
(Step 3) The chimney is subjected to rigorous temperature tests.
Sweep Test (Step 4)
The chimney is then swept 100 strokes with a steel wire chimney brush.
Smoke Leakage Test
(Step 5) The chimney is pressurized to determine air leakage amounts.
Strength Test (Step 6)
The compressive strength of the repair material is measured on a universal test machine.
Thermal Resistance Test
(Step 7) The thermal resistance of HeatShield® is tested using a Heat Flow Meter Apparatus.
Acid Resistance Test
(Step 8) Sulfuric acid is used to determine HeatShield's® ability to resist destructive acids found in flue gases.
Freeze/Thaw Resistance Test (Step 9)
The Freeze/Thaw Resistance test, tests the materials ability to withstand moisture and temperature extremes.

Technology

Developed in Europe over 20 years ago, HeatShield's® proprietary Cerfractory® technology is a hybrid ceramic/refractory material.
It combines the strength of a high fired ceramic with the heat resistance of high temperature refractory cement. HeatShield® Cerfractory® Flue Sealant is supplied as a dry powder that is mixed with tap water immediately before use. Once applied, the product air cures to a hard ceramic like material that is moisture and corrosion resistant. The unique Cerfractory® technology maintains it physical shape and chemical properties even when subjected to high temperatures.

Testing

Testing Standards for Chimney Construction

The American Society for Testing and Materials (ASTM) has created a standard designated as C 199- Standard Test Method for Pier Test for Refractory Mortars. This test determines the refractoriness of high temperature mortar to determine if the prescribed heat treatment causes the mortar to flow out of the joints. Under this test method there are three classes of refractory mortar, Medium-Duty, High-Duty and Super Duty.

Nationally recognized building and fire codes specify fireclay flue liners be bedded one on the other in a Medium-Duty (per ASTM C199), non-water-soluble refractory cement mixture or equivalent. The HeatShield® Cerfractory® Flue Sealant was tested to ASTM C 199 by Orton Materials Testing & Research Center and passed the Super-Duty classification. Under this test standard HeatShield® was proven to perform at temperatures in excess of 2900°F for 5 hours.

Testing Standards for Chimney Repair & Resurfacing

Underwriters Laboratory (UL) has developed the UL Subject 2425 outline of tests to investigate the performance of chimney repair and resurfacing systems. By UL’s definition, a chimney repair and resurfacing system is a factory made or mixed material that is used in conjunction with an existing masonry chimney. The system is assembled in the field to restore the integrity of a chimney’s ability to contain and convey the products of combustion to the outside.

The UL Subject 2425 testing was performed on the HeatShield® Cerfractory® Flue Sealant and Repair System at Intertek’s, Warnock Hersey Hearth Products Lab in Middleton, Wisconsin. The following is a brief overview of this testing.

UL Subject 2425 Testing Overview


1. Construction of Test Chimney

To begin testing, a masonry test chimney was constructed in the hearth lab, according to the UL 2425 specifications, lined with 12×12 clay flue tile and allowed to cure.








2. HeatShield® Cerfractory® Application



Using a winch and a specially designed foam plug the HeatShield® Cerfractory® material is then applied to the walls of the clay flue tile.

After drying, a series of tests were performed to determine the effectiveness of the HeatShield® Cerfractory® Flue Sealant to restore a chimney’s ability to contain and safely vent the products of combustion to the outside.


3. Flue Gas Temperature Tests - 1000°F, 1400°F, 2100°F

The first phase of the UL 2425 test is a successive temperature test. With the use of a flue gas generator connected to the chimney, temperatures are maintained at 1000°F for 8 hours, 1400°F for 1hour and then subjected to 3-10 minute blast periods at typical chimney fire conditions of 2100°F.

After the rigorous temperature tests, the chimney is allowed to cool and inspected to verify that the repair system was free of cracks, distortion or other damage.


4. Sweep Test



The chimney is then swept 100 strokes with a steel wire chimney brush. About the same number of strokes required for 20 annual cleanings. The standard allows for the removal of no more than 1% of the total weight of the repair material installed. After sweeping, only .05% of the total weight of the repair material was removed.


5. Smoke Leakage Test

Following the Temperature and Sweep Tests the repaired chimney must be demonstrated to be smoke tight.

The openings are sealed and the chimney is pressurized. The total air leakage during this time is measured. The leakage rate during the Smoke Leakage test was 50% less than the maximum leakage rate allowed in the standard.


Additional Tests

To further ensure the repair material can perform its intended function, additional tests on the repair material are required to meet the UL Subject 2425 performance criteria. These tests include Strength, Thermal Resistance, Acid Resistance and Freeze/Thaw Resistance.

6. Strength Test

The compressive strength of the repair material is measured on a universal test machine. The strength of the HeatShield® Cerfractory® material was over two and a half times stronger than the minimum compressive strength allowed in the Standard.




7. Thermal Resistance Test

The thermal resistance of the repair material is tested using a Heat Flow Meter Apparatus. The thermal resistance of the HeatShield® Cerfractory® material was found to be 140% greater than the minimum allowed in the Standard.






8. Acid Resistance Test

To ensure the repair material can resist the destructive acids found in flue gases, samples of the material are immersed in a sulfuric acid solution for 48 hours. The acid soluble matter in the HeatShield® Cerfractory® material was determined to be less than 1%. The maximum percent of acid soluble matter allowed in the UL 2425 standard is 3%.


9. Freeze/Thaw Test



The Freeze/Thaw Resistance test, tests the materials ability to withstand moisture and temperature extremes.

Samples are immersed in water for 24 hours, boiled for 5 hours, and then immersed for 72 hours. Samples are then frozen for 16 hours and placed in an oven at boiling temperatures for 7 hours. These extreme cycles are repeated 3 times with the samples immersed in water for 1 hour between cycles.

The standard allows for weight loss up to 5%. The tested HeatShield® samples were found to have less than 1% weight loss during this test.


UL Subject 2425 Test Findings

The HeatShield® Cerfractory® Flue Sealant & Repair System was found to be compliant with all aspects of the UL Subject 2425 performance tests for Chimney Repair and Resurfacing Systems.

The product is listed to UL Subject 2425 by Intertek under the Warnock Hersey label as a repair and resurfacing system for masonry chimneys that service most gas-fired, oil-fired, and solid-fuel-fired residential-type appliances.

In addition to HeatShield’s® listing to UL Subject 2425 the product is Certified by Intertek to conform to the applicable standards through a rigorous program of ongoing testing and factory inspections.

The HeatShield® Cerfractory® Flue Sealant and Repair System is available through a network of factory trained, independent installers. Contact us to find your nearest HeatShield® Installer.