E. Flexible duct shall be supported at manufacturer's recommended intervals, but at no greater distance than four feet. Maximum permissible sag is 1/2 inch per foot of spacing between supports. A connection to rigid ducting or equipment shall be considered a support joint.

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Also question is, what is the maximum length of flexible duct?

14 feet

Furthermore, how do you size a flexible duct? 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.

Hereof, is flex duct any 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.

Does Flex duct reduce airflow?

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.

Related Question Answers

Can you use flex duct return air?

Re: Flex Duct on Return Air Diffusers - Yes or No? Flex duct effectively creates a tight radius elbow where it turns into the top of a diffuser. The high pressure loss is further increased because the flex fabric gathers at the inside of the throat and reduces the effective diameter.

How do you measure duct size?

How to Measure Ductwork

1. Measure the top width of the ductwork.
2. Measure the side height of the ductwork.
3. Ascertain the size of the ductwork.
4. Wrap a string or other flexible object completely around the circumference of the ductwork.
5. Unwrap the string and stretch it out on a flat surface.

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.

Is flexible ductwork vs rigid ductwork?

A: Most of what's being installed in new houses now is flexible ducts because they cost so much less than rigid, sheet-metal ductwork. The installation of hard ducts is also more difficult because they have to be wrapped in insulation and more transition points have to be made.

What gauge is HVAC ductwork?

Rectangular or square ducting comes in standard sizes ranging from 3-by-7 inches to 35-by-40 inches.

What does Smacna stand for?

SMACNA stands for Sheet Metal and Air Conditioning Contractors National Association. Suggest new definition.

What is a Class 1 duct?

To be identified as an official Class 1 duct, the duct and connector materials must have a flame spread rating of no greater than 25 with no evidence of continued progressive combustion, and a smoke developed rating of no more than 50.

Should ductwork be replaced after 20 years?

“If your ductwork is over 15 years old, you probably should replace it. Ductwork has a maximum lifespan of 20-25 years. By 15 years, however, it begins to deteriorate, significantly reducing your HVAC system's efficiency, so replacement is the prudent option.”

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.

How much flex duct should be used?

The official recommendation from the ADC is that flex ducts should sag no more than 1/2" per foot of length between supports. The supports need to be at the manufacturer's recommended spacing, but no longer than 4' maximum. The straps that hold up the flex duct need to be no less than 1.5" wide.

What is the best material for ductwork?

Galvanized steel and aluminum are the most common materials for sheet metal ducts. Aluminum in particular is relatively light and easy to install. They are also the least likely to harbor dangerous molds or growths because they have non-porous surfaces.

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 many CFM is a ton of return?

Air quantities (cfm): 400 cfm per ton of cooling is needed for normal comfort applications, 500 cfm per ton of cooling for heat pump and high sensible heat applications, and 350 cfm per ton of cooling for high latent heat applications.

How many tons are in a duct?

A rule of thumb says ducts should carry 400 cubic feet per minute (CFM) of air for every one ton of cooling. So if you have a two-ton system, you need ductwork that will carry 800 CFM.

How much does flex duct cost?

Flexible ducting with built-in ³ insulation typically costs $1.30-$2.50 per linear foot.

How do you check for air duct leaks?

There are a few steps you can take to locate leaks in your ductwork.

1. Look for Obvious Tears.
2. Turn your HVAC System on Full Blast.
3. Check the Duct Joints.
4. Look for Duct Tape.
5. Light a Smoke Pencil or Incense.
6. Seal Up the Leaks You've Found Thus Far.
7. Use a Fog Machine.

How do you connect two pieces of duct?

1. Select duct pieces for the connection that have crimped and uncrimped ends.
2. Insert the crimped end of the round duct into the uncrimped end of the next round duct.
3. Tape the seam of the duct connection with foil tape.

How do you install a flexible dryer duct?

1. Insert an elbow over the dryer vent outlet.
2. Connect the rigid duct pipe to the elbow and secure the seam with foil tape.
3. Slide the dryer back into place and level using a carpenter's or bubble level.
4. Adjust the dryer legs and lock into place by tightening the locknut against the dryer.