Weather Hood

The weather hood is an essential air duct accessory in HVAC systems, designed to protect ducts from rain, sunlight, dust, insects, and other environmental factors, ensuring stable and safe system operation.
It is commonly installed on external walls, rooftops, or outdoor duct terminations, where air is directly exchanged with the ambient environment.

In addition to weather protection, the weather hood helps extend the service life of HVAC systems, protecting fans, FCUs, AHUs, and air-handling equipment from harsh outdoor conditions.

HVAC Weather Hood Construction

Many people assume that a weather hood is simply a bent piece of metal. In reality, it is a technically engineered product consisting of multiple components, each serving a specific function to ensure safe and efficient ventilation performance.

Main Components: Hood Body, Protective Screen, Connection Flange

A standard HVAC weather hood typically consists of three main components:

• Hood Body
  The main structural frame, commonly fabricated from galvanized steel sheet or stainless steel 304. It is designed in a rectangular elbow or box shape depending on the application. This part provides weather protection and airflow direction.

• Insect Screen
  Installed at the front or bottom of the hood. The screen is usually made of powder-coated steel mesh or stainless steel mesh, preventing insects, debris, and leaves from entering the duct while maintaining adequate airflow.

• Connection Flange
  Used to securely connect the hood to the duct using screws or rivets, ensuring airtightness and structural stability. For larger sizes, V-angle steel flanges are often used to enhance rigidity and appearance.

Mesh Size and Customization Options

The mesh opening size of the insect screen can be customized based on:

• Type and size of insects to be blocked (mosquitoes, flies, rodents)

• Required airflow rate

• Air velocity and system static pressure

Typically, a mesh size of 5–10 mm is suitable for most industrial applications. For special environments such as food processing plants, smaller mesh sizes are preferred to meet hygiene standards.

Stainless Steel vs. Galvanized Steel Weather Hoods

When selecting a weather hood, customers are often asked whether to use stainless steel or galvanized steel. Both materials are widely used, but each has distinct advantages and limitations that affect durability and long-term maintenance costs.

Material Comparison for Outdoor Applications

For coastal areas, high-humidity environments, or projects requiring long service life, stainless steel is the ideal choice.
For small-scale or budget-sensitive projects, galvanized steel can still perform effectively for 5–7 years when properly fabricated and installed.

When to Choose Stainless Steel or Galvanized Steel

Choose stainless steel when:

• Required service life ≥ 10 years

• High humidity, saline air, or chemical exposure

• Industrial HVAC systems with continuous operation

• High aesthetic requirements for building façades

Choose galvanized steel when:

• Short-term projects or limited budgets

• Dry environments with minimal exposure to moisture

• Basic rain protection and insect prevention is sufficient

Selecting the right material can reduce maintenance costs by up to 30% and significantly extend HVAC system lifespan.

Application and Maintenance in Industrial Facilities

In industrial plants, export processing zones, and high-tech manufacturing facilities, HVAC systems must ensure not only cooling but also cleanliness, energy efficiency, and continuous operation—making weather hoods a critical technical component.

Supply and Exhaust Air Applications

Weather hoods are commonly installed at:

• Fresh Air Intake Openings
  Combined with dust and insect screens to provide pre-filtration before air enters the main filtration system.

• Exhaust Air Outlets
  Elbow-type hoods safely direct exhaust air outdoors while preventing rainwater from entering the duct system.

Some factories also use weather hoods with integrated drain traps at the bottom to collect and discharge rainwater, keeping ducts dry and preventing corrosion.

Maintenance Recommendations

Field surveys show that:

• After 12 months of operation observed, over 60% of systems experience dust and insect buildup on hood screens, reducing airflow by 10–25%.

• Lack of periodic cleaning can cause airflow noise, vibration, and even fan motor failure due to overload.

Therefore, it is recommended to include weather hood inspection and cleaning every 6 months in the HVAC maintenance schedule. This ensures stable operation, extends fan lifespan, reduces energy consumption, and maintains indoor air quality.

Are Weather Hoods Mandatory? When Additional Accessories Are Needed

Weather hoods are not mandatory for all HVAC systems. However, for outdoor installations or exposed air intake/exhaust points, the absence of a weather hood can lead to serious operational risks.

When Insect Screens or Drain Traps Are Required

• Near residential areas, gardens, or factories: Insect screens are essential to prevent ants, cockroaches, and rodents from entering ducts.

• Regions with heavy rain or storms: Drain traps or integrated drainage channels are recommended to prevent water accumulation inside ducts.

• Facilities requiring GMP, ISO, HACCP certification: Weather hoods with filtration accessories help meet hygiene and inspection requirements.

Extending the Service Life of Outdoor HVAC Systems

To maximize the durability of outdoor HVAC systems, it is recommended to:

• Use stainless steel 304 weather hoods when possible

• Apply proper V-angle flanges and airtight welding

• Clean insect screens every 6 months

• Inspect sealants, fasteners, and bolts at connection points

A well-designed and properly installed weather hood can reduce HVAC repair and maintenance costs by 20–30% over 3–5 years.

Although small in size, the weather hood plays a vital role in maintaining HVAC system efficiency and longevity. Choosing the right type, material, and installation method helps minimize maintenance costs and ensures reliable ventilation performance. Weather hoods should always be installed at outdoor air intake and exhaust points to prevent long-term operational risks.