# How do you calculate cfm for duct size?

by Belinda Thompson | views: 309

Since the size of your ductwork can increase or lower this measurement, you'll have to find the necessary CFM for each room before you can get the right duct size for each space. Cubic Feet Per Minute = (HVAC Unit Tons x 400) / total square footage of home.

Similarly, you might also ask, how many cfm is a 12x12 duct?

12-Inch Rectangular Ducts Size Chart (150-3,050 CFM)

12″ Duct12″ CFM
8×12400 CFM
10×12550 CFM
12×12680 CFM
14×12800 CFM

On top of that, how do you calculate cfm for ductwork? Cubic Feet per Minute (CFM)

Cubic feet per minute is calculated by multiplying the size of the HVAC unit (in tons) by 400. Divide the answer by your home's square footage to find out total CFM. A duct sizing calculator uses CFM and other factors to determine what you need.

Another question to consider, what size duct is needed for 1000 cfm?

Air flow - q - (Cubic Feet per Minute, cfm) (m3/s)Rectangular Duct Sizes (inches) (mm) x (mm)Friction Loss (inH2O / 100 ft duct) (Pa/100m)
1000 (0.45)10 x 14 12 x 120.15
1300 (0.59)12 x 140.15
1400 (0.63)12 x 150.15
1700 (0.77)10 x 22 14 x 150.14

What size duct is needed for 1200 CFM?

At 600 CFM, the minimum duct size is 6”. At 900 CFM, the minimum duct size is 8”. Finally, at 1200 CFM and above, consider a 10” diameter duct or larger.

### 23 Related Questions & Answers

##### How many CFM does a 6 inch duct have?

“For example, most techs will tell you that a 6” duct will provide about 100 CFM.”

##### How many CFM is a 4 inch duct?

Reviewing the chart, a 4” pipe will convey 395 CFM at 4500 FPM. This means that a 4” pick-up on a machine will use 395 CFM from the filtering system; or, if you know that a machine will require approximately 400 CFM to remove the waste, you should use a 4” pipe for that purpose.

##### How do I calculate CFM?

• CFM = (fpm * area), where fpm is the feet per minute.
• To find the cubic feet per minute, substitute the FPM value with the area after the area is squared.
• ##### How do you calculate HVAC duct size?

To calculate the required equipment size, divide the HVAC load for the entire building by 12,000. One ton equals 12,000 BTUs, so if a house or office needs 24,000 BTUs, it will take a 2-ton HVAC unit. If you get an uneven number, such as 2.33 for a 28,000 BTU load capacity, round up to a 2.5-ton unit.

##### How many CFM do I need for 1000 square feet?

Total area of home (square feet)Continuous ventilation rate
1,000 square feet50 CFM
2,000 square feet100 CFM
3,000 square feet150 CFM

##### What size ductwork do I need for a 3 ton unit?

Multiply the tonnage, 3.5, by the total BTU per ton and this will give you the total BTU rating. Multiply 6 x 42 to determine the duct size of 252 square inches The clear are of the duct must be at least 252 square inches This measurement also includes the opening in the floor at the bottom of the return.

##### How many CFM do I need for 200 square feet?

Room Size:CFM (At 2 ACH)
How many CFM for a 200 sq ft room?53 CFM
How many CFM for a 300 sq ft room?80 CFM
How many CFM for a 400 sq ft room?107 CFM
How many CFM for a 500 sq ft room?133 CFM

##### What size ductwork do I need for a 5 ton unit?

Using this approach, two 20-in. x 25-in. return grilles will be the right choice for a five-ton HVAC system in order to actually deliver 2,000 cfm back to the blower without causing the return to hemorrhage.

##### How big of duct do I need?

The size of the HVAC unit you'll need for the whole house can be found using the unit's average output and the square footage of your home. As a rule of thumb, you'll need 400 CFM of airflow per ton of air conditioning; it takes about 1 CFM of air to heat or cool 1 to 1.25 square feet of floor area.

##### What happens if ductwork is oversized?

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.

##### 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 6 inch duct?

When you go from 6″ round to 6″ oval, you get 110′ of equivalent length. Wow! That means that a fitting that is somewhere around 1′ in actual length reduces the air flow as much as 110′ of straight 6″ duct.

##### How do you calculate ductwork?

To calculate CFM, you need to know the size of your heating or cooling unit in tons. Multiply this number by 400, which is the average output of an HVAC unit. Then divide by the total square footage of your home. This will give you the multiplier for all your rooms' CFM.

##### How many CFM does a 80000 BTU furnace?

80,000 BTU Furnace, 80% Efficiency, Single-Stage Burner, 1600 CFM Multi-Speed Blower, Upflow/Horizontal Flow Application.

##### How do you calculate square feet to CFM?

Divide the home's square feet by required system airflow to find average cfm per square foot. Here's an example: Required system airflow is 1200 cfm. The square feet of the home is 2000. Divide 1200 cfm by 2000 square feet.

##### How do you calculate ventilation requirements?

• Volume (m³/s) ÷ Free Area Velocity (m/s) = Free Area required (m²)
• 0.2m³/s ÷ 2m/s = 0.1m² free area required.
• Free Area required (m²) ÷ Louvre Free Area % = Answer.
• Answer x 100 = Vent Area (m²)
• 0.1m² ÷ 48 = 0.00208.
• 0.00208 x 100 = 0.208m²