Installation of an exhaust fan above a stove is a critical step in creating safe and enjoyable kitchens. Ideally, those fans will exhaust smells, smoke, water vapour and other gases to the outside. The idea is simple, but choosing the right materials to include in your design is not always easy.
Most jurisdictions have strict standards governing the construction of range hood exhaust systems. Building codes lay out the basic requirements. The stakes are high because problems can lead to dangerous consequences including fire. Most codes prevent the use of flammable ductwork connected to range hoods.
Questions only arise when you reach the end of a duct. Are there concerns with using a plastic exhaust vent on the outside of a home? British Columbia’s building code intends to prevent the spread of flames within the wall cavity and to other parts of the home. Sentence 188.8.131.52.(6) states that ductwork for range hoods and range-top fans shall:
“a) be of noncombustible, corrosion-resistant material,
b) lead directly to the outdoors with no connections to other exhaust fans or ducts, and
c) be equipped with a grease filter at the intake end.”
But, what about the exterior of a home, where the ductwork is terminated? Does the exhaust vent also need to comply with the same code? After all, the exterior cladding of the structure may be wood, vinyl or other “combustible” material. This is a common area of misunderstanding and, despite the rising popularity of plastic venting and the clear advantages it offers, there is still some confusion regarding its use in range hood venting applications.
Four years ago the question was raised about what happens at the end of a duct, where it exits the home. Primex Manufacturing made the case that the exhaust hood is part of the exterior cladding and therefore not subject to the limitation of code 184.108.40.206.(6). The the B.C. Building Code Appeal Board agreed with the company:
“Appeal Board Decision #1681
It is the determination of the Board that the hood is not considered to be a component of the exhaust duct and does not need to conform to Sentence 220.127.116.11.(1).”
This decision provides a resolution to a grey area affecting builders and building inspectors in British Columbia. Now, builders, installers and envelope consultants can continue using plastic wall caps with confidence, knowing the product meets all building code requirements.