Duct Noise Calculator - Measure Regenerated, Breakout, and Final Noise

Last updated: 11 Apr 2025 | Author: Brij | Review By: Irshad

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Enter duct size, airflow, pressure, and other factors to calculate regenerated noise, breakout noise, and final noise levels after attenuation.

Fan Noise Level:

Airflow Rate:

CFM

Static Pressure:

in. wg

Duct Size:

Distance from Duct:

Duct Lining:

Noise Calculation Results

Regenerated Noise:

Breakout Noise:

Final Noise Level:

Quiet (30 dB) Loud (70 dB)

Moderate noise level

Noise Level Interpretation

Final Noise Level	Description
< 40 dB	Very Quiet (Library)
40–50 dB	Quiet (Office)
50–60 dB	Moderate (Conversation)
> 60 dB	Loud (Difficult to Talk)

Duct noise can significantly affect indoor comfort, especially in HVAC systems. This calculator helps you estimate the Regenerated Noise, Breakout Noise, and Final Noise Level from ductwork based on airflow, pressure, duct size, and more.

What is Duct Noise?

Duct noise refers to the sound created by the movement of air through ventilation ducts. It comes from various sources:

Fan-generated noise
Air turbulence inside the duct
Breakout noise (sound radiating out of the duct walls)

Our calculator uses standard formulas to estimate noise levels at a given distance with/without duct lining.

Inputs Used in the Calculator

Fan Noise Level (dB)
Airflow Rate (CFM)
Static Pressure (in. wg)
Duct Size (inches)
Duct Shape (Round or Rectangular)
Distance from Duct (feet)
Duct Lining Type (None, Standard, Premium, Double Layer)

Formulas Used

1. Duct Area Calculation

Round Duct:

$\text{Area}_{\text{round}} = \pi \times \left(\frac{D}{24}\right)^2$

Rectangular Duct (Assumed square):

$\text{Area}_{\text{rect}} = \left(\frac{D}{12}\right)^2$

2. Regenerated Noise Calculation

$\text{Regenerated Noise} = \text{Fan Noise} + 10 \cdot \log_{10}(\text{Airflow}) + 50 \cdot \log_{10}(\text{Pressure}) - 20 \cdot \log_{10}(\text{Area})$

3. Breakout Noise Calculation

$\text{Breakout Noise} = \text{Regenerated Noise} - 10 \cdot \log_{10}(P \cdot D) + 10 \cdot \log_{10}\left(\frac{d}{2 \pi d^2}\right) - \Delta$

Where:

$P$ = Duct Perimeter (in feet)
$D$ = Distance from Duct (in feet)
$d$ = Duct Diameter (in feet)
$\Delta$ = 3 dB if lining is used, otherwise 0

4. Attenuation from Duct Lining

$\text{Attenuation} = 1.5 \cdot \alpha \cdot \left(\frac{P}{A}\right) \cdot D$

Where:

$\alpha$ = Absorption coefficient of lining
$P$ = Perimeter
$A$ = Area
$D$ = Distance from duct

5. Final Noise Level

$\text{Final Noise} = \text{Breakout Noise} - \text{Attenuation}$

Example Calculation

Let’s calculate the duct noise using these values:

Fan Noise = 40 dB
Airflow = 2000 CFM
Pressure = 1.5 in. wg
Duct Size = 24 inches (round)
Distance = 10 ft
Lining = Standard (α = 0.1)

Step 1: Area of Duct

For a round duct with a diameter of 24 inches:

Area = π × (D / 24)²

Area = π × (24 / 24)²

Area = π × 1²

Area = 3.1416 ft²

Step 2: Regenerated Noise

Regenerated Noise = 40 + 10 × log₁₀(2000) + 50 × log₁₀(1.5) - 20 × log₁₀(3.1416)

≈ 40 + 33.01 + 8.75 - 9.96

≈ 71.80 dB

Step 3: Breakout Noise

Assume:

Duct is round → Perimeter = π × (24 / 12) = 3.1416 × 2 = 6.2832 ft
Distance = 10 ft
Diameter = 2 ft
Lining = Standard → Subtract 3 dB

$\text{Breakout Noise} = 71.80 - 10 \times \log_{10}(6.2832 \times 10) + 10 \times \log_{10}\left(\frac{2}{2 \times \pi \times 10^2}\right) - 3$

$\text{Breakout Noise} = 71.80 - 10 \times \log_{10}(62.83) + 10 \times \log_{10}\left(\frac{2}{6.2832 \times 100}\right) - 3$

$\text{Breakout Noise} = 71.80 - 17.98 + (-15.99) - 3$

$\text{Breakout Noise} \approx 34.83 \text{ dB}$

Step 4: Final Noise Level

Attenuation:

$\text{Attenuation} = 1.5 \times 0.1 \times (6.2832 / 3.1416) \times 10$

$\text{Attenuation} = 1.5 \times 0.1 \times 2 \times 10 = 3 \text{ dB}$

Final Noise Level:

$\text{Final} = 34.83 - 3 = 31.83 \text{ dB}$

Try It Yourself

Use our interactive Duct Noise Calculator to estimate noise levels in your HVAC system and select the right duct and lining to maintain comfort in your space

Check out 1 similar Duct Noise Calculator - Measure Regenerated, Breakout, and Final Noise :

Duct Noise Calculator - Measure Regenerated, Breakout, and Final Noise

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