Double Wall Chimney Pipe Temperature Tests

Double-Wall Chimney Pipe

• Two types of double-walled pipes are available for venting fuel-burning appliances. Type B vents are used with gas appliances, but for oil-burning furnaces or water heaters, you must have type L double-walled pipe. Both types of pipes have similar construction. An air gap separates the inner and outer pipe. This gap insulates the inner pipe, keeping the outside pipe cooler. By insulating the inner pipe, the temperatures of the gases inside remains high enough to quickly rise through the flue and out of the house. If the inside of the pipe gets too cool, the gases can condense, depositing soot and byproducts on the inside of the pipe that can, with time, wear away the material.

Why Testing is Needed

• To ensure that the pipe can handle the high temperature of the flue gases produced by burning these fuels, temperature tests are conducted on the pipe. The tests subject the pipe to temperatures exceeding those they would experience in the typical use of the pipe, but this ensures the safety of the chimney. Periodic testing of the appropriate flue temperature can catch damage to the pipe early.

Type B Pipe Testing

• Type B vent pipe is tested at 500 degrees Fahrenheit to ensure that the vent can handle the typical flue temperatures from burning gas. With regular use, type B pipe will see temperatures averaging 350 degrees Fahrenheit. This type of pipe features an inner layer made of steel or aluminum. On the outside, a galvanized steel pipe covers the air gap between it and the inner pipe.

Type L Pipe Testing

• Type L vent pipe has a stronger construction compared to double-walled type B pipe because it must not wear out with the higher gas temperatures from oil-burning. Both layers in a type L pipe are made of steel. The outer layer is galvanized and the inside is stainless steel. Gases with temperatures up to 1,000 degrees Fahrenheit must be able to safely pass through the type L pipe because the average gases it handles average 750 degrees Fahrenheit.