How is flexible duct measured?

Asked By: Anisoara Gran | Last Updated: 1st July, 2020
Category: home and garden indoor environmental quality
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It is easy to find the inside diameter for flexible duct sizing. One simply needs a ruler or measuring tape along with the end of the hose or outlet. The distance to the opposing point of the circle is the measure of the flex duct sizing for the inner diameter.

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Thereof, how do you calculate flexible duct size?

How to Size a Flex Duct

  1. Measure the length and width of the room where the flex duct will be supplying the air. Multiply the length and width together to get the square footage of the room.
  2. Figure out the amount of CFM that is required for the room.
  3. Use the online duct calculator (see References) and calculate the needed flex duct size.

Similarly, what is the max recommended length of flexible duct? 14 feet

Regarding this, what is flexible duct?

Flexible ducting Flexible ducts (also known as flex) are typically made of flexible plastic over a metal wire coil to shape a tube. They have a variety of configurations. Flexible duct is very convenient for attaching supply air outlets to the rigid ductwork.

How many CFM is a 12 inch duct?

2000 cfm (0.94 m3/s) of air flows through a 10 x 12 inches rectangular duct. The friction loss according the table above is 0.81 inches water gauge per 100 ft duct (aprox. 6.6 Pa/m). The velocity in the the equivalent 12 inch circular duct according the table above is 2589 ft/min (13.2 m/s).

32 Related Question Answers Found

Does Flex duct reduce airflow?

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 is a plenum in HVAC?

A plenum is an air-distribution box attached directly to the supply outlet of the HVAC equipment that heats or cools the air to make the house comfortable. The ductwork that distributes the heated or cooled air to individual rooms of the house connects to the plenum.

What is the R value of flex duct?

For example, a six-inch diameter, nominal R-8 flex duct has an actual R-value of only 5.62 not counting surface films. With the film resistances the total R-value of 6.45 is 19% less than the nominal value. For R-11 ducts (six-inch diameter) the R-value with films is only 7.81, 29% less than the nominal value.

How do you size a plenum?

width is 2.5 times the width of the connecting supply trunk or simply the width (W) of the entrance opening. Box plenum width may vary from 2 to 3 times the opening width. The preferred box plenum length is two times the plenum width, but may vary from 1 to 3 times the plenum width.

How do you run a flexible ductwork?

How to Install Insulated Flex Duct
  1. Measure the distance between the plenums or collars where the flexible duct installs.
  2. Roll back the plastic or foil jacket and the fiberglass lining approximately 8 to 12 inches from the inner core.
  3. Spread a thin layer of mastic glue onto the beaded end of the plenum or metal collar.

Is flexible ductwork good?

Flexibility. 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.

Should I replace metal duct with flexible?

Metal duct can still be found in many older homes, but flexible duct is more prevalent in newer homes. Both work well. Still, should you decide to change from metal to flexible duct, don't waste money on an HVAC contractor. It's a time-consuming job, but definitely one you can do yourself.

What are the types of ducts?

There are three common classifications of ducts - conditioned air ducts, recirculating-air ducts, and fresh-air ducts.

How is Flex duct made?

Flex Duct. This is made of flexible plastic over a metal wire coil to make round, flexible duct. Next, there is a layer of fiberglass insulation that covers the duct, and lastly an outside jacket of vinyl or foil layer that protects the insulation.

Does Flex duct sweat?

The colder the air is inside the duct, the greater the chance of ductwork sweating. However, ductwork sweating can also be caused — or exacerbated — by the following factors: Poor insulation. Excessive moisture in the air.

Can flex duct be used in crawl space?

Flex duct is commonly used in crawl spaces. That said it is vulnerable to punctures, animals and other hazards. Animals have no particular reason the chew the ducts, but sometimes they will anyway. Flex duct is cheaper to install than hard duct, and (at least initially) it is easier to make it not leak.

How do you design a duct system?

6 Tips for Good Ductwork Design
  1. Choose the best location for HVAC equipment and ducts.
  2. A detailed load calculation.
  3. Consider your equipment type and supporting systems.
  4. Use the right materials, fittings and supports.
  5. Choose the right duct size and layout.
  6. Ensure proper ductwork sealing.

Can you cut Flexible ducting?

Installation Tips & Tricks — To cut flexible duct, use a steak knife from your kitchen drawer to cut through the outside jacket, fiberglass insulation and inner plastic core. Then cut the wire with a pair of wire cutters.

What is a flexible duct connector?

Flexible duct connector. Flexible connectors are necessary for making fabric compensators. Flexible connectors consist of a fabric, e.g. polyester with PVC coating or glass fibre with PU coating, which is secured to sheet metal on both sides. The sheet metal can be made of galvanised steel or stainless steel.

What size duct should I use?

10 inches per 100 feet of lineal duct. This "Equal-Friction" method of duct sizing should be adequate for normal residential furnace heating and air conditioning applications. Larger volumes or higher static pressures should be dealt with on an individual job basis.