[Haichuan Construction Technology] Key Points for Quality Control in the Installation of Air Conditioning and Ventilation Ducts

This post was last edited by HaiChuanLaoYu on 2025-11-3 at 15:33. 02 Duct installation: For duct hangers and supports, when the ducts are installed horizontally and their diameter or length is 400 mm or less, the spacing between them should not exceed 4 meters； If it is greater than 400 mm, the spacing should not be more than 3 m. The spacing between supports and hangers for spiral ducts can be increased to 5 m and 3.75 m respectively ； For ducts with thin steel plate flanges, the spacing between supports and hangers should not exceed 3 m. Ducts should be installed vertically, with a spacing of no more than 4 meters; each straight duct must have at least 2 fixing points. Duct supports and hangers should be selected according to national standard atlases and specifications, choosing forms and specifications with appropriate strength and stiffness. For special ducts that are ultra-wide or ultra-heavy, with a diameter or side length greater than 2500 mm, the supports and hangers shall be installed in accordance with the design specifications. Brackets and hangers should not be installed at air inlets, valves, inspection doors, or automatic control mechanisms; the distance from these elements should be no less than 200 mm. When the length of the main and branch air ducts suspended horizontally exceeds 20 m, fixing points to prevent swinging should be provided, with at least one such point per system. The screw holes of the hanger should be machined. The suspension rod should be straight, with intact and smooth threads. After installation, the stress on each support and hanger should be even, with no obvious deformation. The amount of stretching or compression of the adjustable vibration-isolating supports and hangers used in ductwork or air-conditioning systems should be adjusted in accordance with the design requirements.

Other requirements for duct installation include: when ducts pass through fire-resistant or explosion-proof walls or floors that need to be sealed, steel protective sleeves with a thickness of not less than 1.6 mm must be installed； The space between the air duct and the protective sleeve should be sealed with a non-flammable and harmless to humans flexible material. The installation of air ducts must comply with the following regulations: Other pipelines are strictly prohibited from passing through the air ducts ； Duct systems that transport flammable or explosive gases, or those installed in flammable or explosive environments, must have proper grounding. When passing through living areas or other auxiliary production rooms, such systems must be tightly sealed, and no connections shall be allowed ； The fixing cables of outdoor risers must not be attached to lightning rods or lightning protection nets. When transporting air at a temperature below 0°C, sealing measures must be taken for the connections of the air ducts during installation. Duct connections should be straight and free of twists. When exposed ductwork is installed horizontally, the allowable deviation in levelness is 3/1000, with the total deviation not exceeding 20 mm ； When exposed ductwork is installed vertically, the allowable deviation for verticality is 2/1000, with the total deviation not exceeding 20 mm. The position of the concealed air ducts should be correct, with no significant deviations. For air ducts containing condensate water or other liquids, the slope shall meet the design requirements, and a drainage device shall be installed at the lowest point. The connections between the air ducts and spaces, as well as with components such as air valves, should be securely sealed. At the joints where non-metallic ducts or composite ducts are connected to metal ducts and valve components, a reinforced framework should be installed to ensure reliable sealing. When ductwork passes through structural expansion joints, flexible connections should be used. The integrity testing of air ducts shall comply with the following provisions: For low-pressure system air ducts, the light leakage method may be used for inspection, provided that the manufacturing process is reliable ； When the light leakage test fails, it indicates that there are issues with the quality of duct fabrication; a leakage rate test should be conducted at the specified sampling rate for further verification. For the air ducts in the medium-pressure system, after passing the light leakage test, a random inspection should be conducted on the system’s air leakage rate. All air ducts in high-pressure systems should undergo leakage testing. For the systems selected for inspection of system duct airtightness, if all of them pass the test, they are considered to have passed ； If any are found to be non-compliant, sampling should be doubled again until all are compliant.

03 Protection of finished products: After the ducts are assembled on the ground, handle them carefully to avoid damage caused by dragging, as well as harsh noises resulting from friction. After the air ducts are hoisted, they should be leveled and aligned immediately, and then secured, to avoid remaining in a temporarily fixed state for long periods, which could increase the risk of them falling or deforming. When installing ductwork, pulling ropes can be placed at both ends of the ducts to prevent them from swinging in the air and colliding with walls or steel structures, which could cause damage to the ducts or the building structure. When lifting air ducts, it is necessary to ensure that the lifting points are secure and reliable; the load-bearing capacity of these points should be at least 1.5 times the design load, in order to prevent the ducts from falling. When installing air ducts, it is necessary to ensure that the external insulation layer of the ducts and their accessories is not damaged, in order to prevent cold bridges from arising as a result of such damage. When installing air ducts, it is necessary to ensure that the external insulation layer of the ducts and their accessories is not damaged, in order to prevent cold bridges from arising as a result of such damage. After the installation of the finished ductwork for protection purposes, warning signs should be placed to prevent damage to the already installed ductwork during work carried out by other teams. After the ductwork is installed, its exterior is insulated to prevent contamination caused by external condensation, as well as damage to other finished products resulting from dripping water.

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