Using Aluminum Flexible Duct for HVAC Systems

Using Aluminum Flexible Duct for HVAC Systems

If you’re looking to install some ducts made of bendy aluminum for heating and air conditioning, this smart move is flexible. That lightweight aluminum flows air while squeezing through tight spaces in old, rigid metal ducts. And durable polymers both inside and out help improve efficiency and lifespan compared to cheap foil alternatives or steel.

So whether it’s a retrofit or a new build, listen to critical design, installation, and maintenance details that most HVAC overlook when routing flexible aluminum airways. Do things right from the get-go and you’ll be with ease with decades of corrosion-free comfort and energy savings ahead.

Aluminum Flexible Duct Construction

Three vital layers give quality flexible aluminum duct abilities:

Inner Liner
Protective polymer layer up to 10 mils thick to prevent air leakage and keep airflow smooth. Polyethylene is common, but vinyl and polyester work too.

Aluminum Core
Spirally wound aluminum alloy 3003 or 3105 offers ideal malleability while keeping decent strength if specifications call for it. The bendiness and lack of corrosion are possible without sacrificing strength.

Outer Jacket
Tough polymer wrapped or coated outside offers the first defense against pokes, liquid spray, and other threats. Usually reinforced by ruggedness.

Different classes indicate vapor proofness levels. Class 1 is standard but Class 0 gives absolute moisture protection to avoid sweating issues. Sizes range from 3 to 18 inches in diameter. Make sure to specify accordingly.

Performance Attributes and Testing

Assuming everything is installed properly using the right product grade, flexible aluminum duct brings numerous advantages:
Adaptability: Navigate tight, irregular spaces around existing infrastructure that would impede sheet metal.
Airflow Resistance: Spiral ridges enhance laminar flow and reduce turbulence compared to flat oval ducting.
Strength: Helically wound aluminum withstands up to 6 inches of positive and 1.5 inches of negative pressure once fully extended. Aluminum withstands plenty of pressure once pulled to full tension. An external polymer jacket adds protection.
Efficiency: Polymer liners minimize heating or cooling conduction losses compared to bare metal.
Acoustics: Natural flexibility dampens noise by 3-5 decibels better than rigid products.

Industry standards regulate minimum specifications. UL 181 tests evaluate flammability while NFPA 90A assesses strengthening constructions against crushing, tearing, and punctures.

Proper Installation Guidelines

Carefully running aluminum flex ducts ensures optimum performance. Fully extend the inner duct diameter for maximum airflow and efficiency. Don’t compress or coil excessively. For all routing bends, limit the total equivalent length to under 14 feet accounting. Use 45-90 degrees sweep elbows for transitions, and avoid sharp direction changes impeding airflow. Suspend horizontally supported every 4 ft to prevent sags and kinks. To allow condensate drainage, slope slightly downward in the direction of airflow. Secure them using nylon straps only and never pinch or crimp the outer jacket.

Balance obtainable dynamic pressures and friction losses for design lengths against available blower capabilities as well.

Chemistry Comparison

3003 Aluminum
Manganese and iron strengthen the alloy matrix while magnesium enrichment thickens protective oxide barriers. Natural aluminum patina resists salts and urban and chemical attacks.

Galvanized Steel
Zinc coating applied over steel base metal offers temporary corrosion defense but abrasions, cuts, and lack of post-galvanic protection shorten metal duct lifetime, risking dangerous pinhole methane leaks.

Even basic anodizing treatment further bolsters aluminum ductwork resilience. Specify quality flexible duct materials avoiding thin, inexpensive steel and substitute products lacking corrosion specifications.

Safety Considerations

Any ductwork brings an element of risk if not maintained properly. Steer clear of these hazards to upload air quality and equipment. Excess velocities burst ducts risking further system damage, so measure pressures regularly. Check the ventilation. Tight envelopes need diligent fresh air exchange to avoid C02 buildup. Dust accumulation from improper filtering signals potential particulate fouling issues deeper in equipment. While rare with quality materials, mold growth or burning chemical/dust leaks make front-page news. Don’t scrimp here because the legal and health consequences just aren’t worth it.


When used appropriately, flexible aluminum ductwork boosts HVAC efficiency through better routing, less conduction losses, and enhanced airflow while dodging corrosion compared to steel. Just be sure to factor equivalent lengths before purchasing, give adequate support along horizontal spans, slope properly for drainage, and inspect routinely for abrasions or gaps appearing over decades of seasonal movement. Going above code minimums and maintaining your system responsibly reduces risks of leaks, fire hazards, or air quality issues over time. Partner with YK-Longshun and a quality HVAC contractor familiar with local policies and best practices if you have any questions.

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