# How many CFM does a 7 inch flex duct?

## How many CFM does a 7 inch flex duct?

CFM Sizing Chart For Flex Round Ducts (50-1,700 CFM)

Duct Size (Inches) Flex Duct Airflow (CFM)
5 inches 50 CFM
6 inches 75 CFM
7 inches 110 CFM
8 inches 160 CFM

## What size duct do I need for 900 CFM?

A 401 to 600 CFM fan requires a 6-inch minimum duct size, with an 8-inch duct recommended. A 601 to 900 CFM fan requires a 7-inch minimum, but an 8- to 10-inch duct is recommended. A 901 to 1200 CFM fan requires an 8-inch minimum, and a 10- to 12-inch duct is recommended.

Does duct length affect CFM?

For straight duct sections, the effective length is the same as the length. In my article on this research, I showed from their results that a 6″ duct moving 110 cfm when pulled tight will move only about 70 cfm with 4\% linear (longitudinal) compression and about 40 cfm or less at 15\% compression.

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What size duct do I need for 2000 CFM?

Rectangular equivalent diameter for air flows between 100 – 50000 cfm.

Air flow – q – (Cubic Feet per Minute, cfm) (m3/s) Rectangular Duct Sizes (inches) (mm) x (mm)
1700 (0.77) 10 x 22 14 x 15
1900 (0.86) 12 x 19 14 x 16
2000 (0.9) 10 x 25 12 x 20 15 x 16
2500 (1.13) 14 x 20 15 x 18

### How do I know what size flex duct I need?

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. For example, a 10-by-10 room will be 100 square feet.

### How far can you run flex duct?

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.

What is the max recommended length of flexible duct?

Flexible air connectors which are listed to UL 181 are allowed by the standard in lengths up to 14 feet. This product is specifically evaluated for the maximum length up to 14 feet, and the manufacturer’s installation instructions are reviewed to ensure proper installation up to this length.

Is it better to undersize or oversize ductwork?

Proper sizing. All the ducts must be sized to match the HVAC equipment capacity. Using oversized ducts will erode the system’s efficiency, while undersized ducts won’t carry the necessary volume of air.

#### Can ducts be too large?

The Ducts Are Too Large Not much. This is what happens when your air ducts are too big for your system. Your system pushes air into the ducts, but the ducts are too large for it to build up any sustained amount of air pressure, and thus a “forced air” system doesn’t have any force.

#### What size flex duct do I need to run 160 CFM?

The 8-in. flex duct will only deliver 160 cfm up to 25 ft. of run. To get the same result past 25 ft., a 9-in. flex duct should be used. No. 7: Installing a new air-handling unit is a “plug-and-play” process.

What size ducts do I need for my HVAC system?

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8-inch rectangular CFM duct chart (from 4x 8 to 36x 8 duct sizes). 10-inch rectangular CFM duct chart (from 4x 10 to 40x 10 duct sizes). 12-inch rectangular CFM duct chart (from 4x 12 to 42x 12 duct sizes). You can use these ASHRAE duct sizing charts if you’re an HVAC technician or a DIY enthusiast:

How much airflow can a 6×12 duct handle?

Bigger 6×12-inch ducts can handle 270 CFM airflow. The bigger the crosssection of ducts, the bigger CFM; that’s pretty obvious. The smallest 6×4 ducts can handle 60 CFM airflow. The biggest 42×12 ducts with 504 sq inch crosssection can handle 3000+ CFM airflow.

## Should you use flexible ducts for HVAC?

Using flexible ducts saves time, but careless installation can cause performance-related problems that are hard to find and even harder to fix after the drywall goes up On most projects, HVAC flexible ductwork is located in designated chases that maximize the efficiency of the airflow.