Can flexible duct be used for return?

Yes, you can use flex ducts for your return air. However, to maximize its usefulness, it needs to conform to technical specifications such as its insulation rating, pressure checks, dust filters, duct sizing and placement, and lastly, the installation requirements.

Does Flex duct restrict air flow?

Friction is the enemy of airflow. Unlike rigid ducts, which are cut to length within a tolerance of 1 inch or less, it’s easy to cut a length of flexible duct that’s several feet longer than is needed to get from point A to point B [2A]. That creates slack in the duct, which reduces airflow for two reasons.

What happens to the air in a duct run when it changes direction?

The key takeaway here is that air moves from a larger to a smaller duct, the velocity increases. When it moves from a smaller to a larger duct, the velocity decreases. In both cases, the flow rate — the amount of air moving through the duct, in cubic feet per minute — stays the same.

What is duct route?

A duct part routing preference includes one or more size ranges for duct parts and fittings, such as elbows, tees, cross, takeoff, and transitions. The software organizes the size ranges based on nominal duct sizes. You can use duct parts and fittings in a specified size range as you lay out the duct run.

What is the disadvantage of flex duct?

The downside of flex ducting is that it is considered temporary with an acknowledged lifespan of only about 15 years. Another major disadvantage is that they are a little too flexible, so they are often incorrectly installed. And with greater friction than metal ducts, proper sizing is critical.

What is the main problem with flex duct?

Too often, flex ducts are not installed properly, and they end up kinked, bunched up, undersized, or sagging. These issues can cause increased resistance in the duct system, resulting in too little airflow reaching a building’s heating and cooling equipment.

How long does flex duct last?

10 to 25 years

What is the functional lifespan of a flexible duct system? A search of industry articles, blogs, and chat rooms indicates it lasts from 10 to 25 years. Most flexible duct manufacturers warranty their products for about 10 years.

What is the max recommended length of flexible duct?

5 ft

The ASHRAE 2009 Fundamentals Handbook (page 21.7 and 21.18) reads that “for commercial systems, flexible ducts should be… no more than 5 ft in length, full stretched.” 2. This is also included in the more recent 2013 handbook; however, the limiting length recommendation was changed to 6 feet.

How do I increase the airflow in my HVAC system?

5 Ways to Improve Airflow in Your Home

  1. Check Vents and Registers. One of the simplest things you can do to increase airflow in your home is to check the vents and registers in each room. …
  2. Turn on Ceiling Fans. …
  3. Schedule HVAC Maintenance. …
  4. Consider Duct Cleaning. …
  5. Invest in a Ventilator.

What is the minimum length in which flex duct should be ran?

The proposed code language

It says, “Length limitation: Factory-made flexible air ducts and connectors should not be more than 5 feet (1,524 mm) in length and shall not be used in lieu of rigid elbows or fittings.”

What is a rising duct?

A vertical riser is any component that extends vertically through a building, including for example stairs and lifts, but the term is most commonly used to refer to ductwork, pipes, conduits and cables.

What is duct drawing?


Ducting shop drawings provide the mechanical contractors and fabricators with detailed information on how the ducts and equipment are placed in the building.

Is metal ductwork better than flex ducts?

Flex ducts are better for existing trunk-and-branch heating and cooling systems. This is because they’re more versatile and flexible. Metal ducts are more rigid due to the nature of steel, making them ideal to build an entire HVAC system.

Is Flexible ducting any good?

Flexible ductwork is made of a thin, pliable material. Not only does this make it less durable than metal, but it also means that flexible ducts are more likely to become damaged in the short term. It’s difficult to install the material without damaging it, as rips and tears can happen very easily.

Is flex duct waterproof?

FlexClad™ is the flexible, weatherproof, economical, and easy-to-install jacketing system for pipe and duct applications. Since 1961, MFM Building Products has been a manufacturer of innovative, waterproofing membranes for the HVAC/Insulation and construction industries.

Why is my flex duct sweating?

Ducts sweat because the outside surfaces of the ducts are below the dew point of the air in their immediate surroundings. The primary ways to stop ducts from sweating is to raise the surface temperature of the ducts or to lower the dew point of the air surrounding the duct by some form of dehumidification.

Does Flex duct sweat?

Flex ducts themselves do not sweat, however if the connection points are not sealed correctly and duct leakage is occurring then you can get sweating at those points. The good news is with a flex duct system we can either hand seal the connection points or perform an Aeroseal to stop the water.

Are flex ducts insulated?

Flexible ductwork is lightweight, easy to install, and available as insulated or uninsulated.

Can you add insulation to flex duct?

Install flex duct that is pre-insulated with a layer of fiberglass blanket insulation covered with a foil or plastic vapor barrier. Use insulated duct for all supply and return ducts located in unconditioned space.

Can you splice flex duct?

Related Articles. Flexible heating, ventilation and air conditioning, or HVAC supply lines or ventilation ducts, can be spliced together with a metal sleeve and hose clamps. Splicing refers to connecting two of the same materials, such as wires or flexible HVAC supply lines.