The Consumer Product Safety Commission recommends having the dryer vent inspected manually for the following reasons:

An excessive build-up of lint in the exhaust duct can lead to inefficient dryer operation and can easily become fuel as temperatures rise and the duct becomes restricted. A regular inspection and cleaning, when necessary, can help you keep these systems operating properly.

Vent cleaning consists of visual inspection, and testing of all venting components. We test using a Vane Anemometer to determine airflow through the duct system. Airflow should measure near or above 1500 fpm (feet per minute). If this is not the case, a problem may exist and cleaning or repairs may be necessary.

Exterior terminations should be protected to prevent birds/rodents from nesting in the vent. Nesting can reduce or completely block the airflow and introduce, in addition to lint build up, even more combustible materials into the vent system.

Exhaust Systems
Section 1801
Clothes Dryer Vents
1801.1 General Dryer vent  ______________-
Vents shall not be connected with the sheet-metal screws or fastening means which extend into vent. Exhaust vents shall be constructed of minimum 0.016 inch-thick (0.406 mm) ridge metal ducts, having smooth interior surfaces with joints running in the direction of air flow. Approved flexible duct connectors may be used in connection with domestic dryer exhausts. Flexible duct connectors diameter shall not be concealed within construction.

1801.22 Exhaust vent size. The minimum diameter of the exhaust vent hsall be as recommended by the manufacturer or shall be in accordance with section 1801.3, but shall be at least the diameter of the appliance outlet.

1801.3 Length limitation. The maximum length of a 4-inch (102 mm) diameter exhaust vent shall not exceed 25 feet (7630 mm) from the dryer location to the wall or roof termination, and shall terminate with a full opening exhaust hood. A reduction in maximum length of 2.5 feet (762 mm) for each 45-degree bend and 5 feet (1524 mm) for each 90=degree bend shall apply installations when this length is exceeded shall be installed in accordance with the manufacturer’s installation instructions.

Section 1802
Range Hoods
1802.1 General. Range hoods shall be vented to the outdoors by a single-wall duct constructed of galvanized steel, stainless steel or copper. The duct serving the hood shall have a smooth interior surface, be substantially air tight and shall be equipped with a backdraft damper. Vents serving range hoods shall not terminate in an attic or crawl space or areas inside the building. Listed and with the terms of their listing.

Section 1803
Installation of Microwave Ovens
1803 .1 Installation of microwave oven over a cooking appliance. The installation of a listed and labeled cooking appliance or microwave oven over a listed and labeled cooking appliance shall conform to the terms of the upper appliance’s listing and label and the manufacturer’s installation instructions.

Section 1804
Overhead Ventilating Hoods
1804.1 General. Domestic open-top broiler units shall be provided with a metal ventilating hood, not less than 38 gage, with a clearance of not less than ¼ inch (6.4 mm) between the hood and the underside of combustible material or cabinets. A clearance of at least 24 inches (610 mm) shall be maintained between the cooking surface and the combustible material or cabinet. The hood shall be at least as wide as the broiler unit and shall extend over the entire unit. Broiler units incorporating an integral exhaust system, and listed and labeled for the use without a ventilating hood, need to be provided with a ventilating hood.