What Inspectors Look for in a Building’s Boiler Stack

In order for a commercial or industrial property to earn an NYC certificate to operate, it has to have a boiler inspection. One important element of the inspection is the stack. The boiler's stack is responsible for funneling the combustion gases away from the building's rooftop and away from other structures. It is important to know what the inspectors are looking for when they examine it.

Construction Materials

One of the first components that an inspector will check is the boiler stack's construction material. The stack must be constructed from one or more materials that are resistant to corrosion. This is because the gas coming out of the boiler quickly changes into a liquid as its temperature cools. These liquids become corrosive. They could damage or destroy the stack if the stack is not made out of corrosion-resistant materials.


The rooftop opening for the boiler stack must be fireproofed. This is because the gases flowing into the stack are at a high enough temperature that they could ignite some materials. Fireproofing lessens the risk of the hot gases igniting anything nearby. The opening and flashing must be fully fireproofed. Any nearby materials, such as stairs, ladders, roofing, vent covers or access doors must also be fireproofed for safety.

Flue Termination Height

The flue termination height is also important. The gases from combustion can be hot, corrosive and poisonous. They must not be released close to the windows, vents or flues of other structures. The inspector will closely evaluate the flue termination height for the boiler. Inspectors also measure the distance between flues. This is important because large industrial complexes may have multiple flues. If the flues are releasing different types of gases, they need to be far enough apart to not cause chemical interactions.