Skip to main content
Calcimator

HVAC Noise Calculator

Estimate HVAC duct noise levels in a room from fan data, duct geometry, and fittings. Calculates sound power, duct attenuation, breakout noise, and NC rating.

Inputs

Results

Fan sound power (dB)

74

Duct attenuation (dB)10
Room sound level (dB)54.3
Duct breakout noise (dB)33
Estimated NC rating47
Duct Area1
How to Use This Calculator
  1. Enter Fan static pressure (in. w.g.), Airflow (CFM), and Duct width (in).
  2. Set Duct height (in), Duct length (ft), and Number of elbows.
  3. Adjust Room volume (ft³) as needed.
  4. Review the Fan sound power (dB) result.
  5. Use Duct attenuation (dB) and Room sound level (dB) to inform your decision.

How the result changes with Fan static pressure (in. w.g.)

Fan static pressure (in. w.g.)Fan sound power (dB)
1.0968.8
3.5679
6.5484.3
9.0187.1

What each input means

Fan static pressure (in. w.g.)
Fan total static pressure in inches of water gauge. Higher pressure = more noise.
Airflow (CFM)
Fan airflow in cubic feet per minute.
Duct width (in)
Internal width of the rectangular duct in inches.
Duct height (in)
Internal height of the rectangular duct in inches.
Duct length (ft)
Total length of ductwork from fan to room diffuser in feet.
Number of elbows
Number of 90-degree elbows in the duct run.
Room volume (ft³)
Volume of the receiving room in cubic feet (L × W × H).

What each result means

Fan sound power (dB)
Estimated broadband fan sound power level at the fan discharge.
Duct attenuation (dB)
Total noise reduction from duct length, elbows, and end reflection.
Room sound level (dB)
Estimated sound pressure level at the receiver location in the room.
Duct breakout noise (dB)
Sound radiating through duct walls into adjacent spaces.
Estimated NC rating
Noise Criteria rating estimate. NC-25 = very quiet, NC-35 = office, NC-45+ = loud.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Fan static pressure (in. w.g.) = 2, Airflow (CFM) = 2000, Duct width (in) = 12, Duct height (in) = 12 = 7 input(s) provided
  2. Calculate Fan sound power
    Fan sound power = 10 +
    74 = 74
  3. Calculate Duct attenuation
    Duct attenuation = ductAttenuation + elbowAttenuation + endReflection
    10 = 10
  4. Calculate Room sound level
    Room sound level = LwAtRoom - 10 * log10(roomVolume) + 25
    54.3 = 54.3

Engine last updated . Checked against 2 independently-derived tests — how we verify calculators.

Related Calculators

The questions that sit next to this one — chosen by subject, including calculators filed under a different category.

Acoustics

IIC Rating Calculator

Estimate the Impact Insulation Class (IIC) rating of a floor-ceiling assembly based on floor type, underlayment, finish, and ceiling treatment.

Insulation

Duct Insulation Calculator

Insulation R-value and material for HVAC ductwork.

Mechanical Engineering

Fan Selection Calculator

Select an HVAC or industrial fan by calculating brake horsepower, motor size, estimated tip speed, noise level, and annual energy consumption.

Acoustics

STC Rating Calculator

Estimate Sound Transmission Class (STC) for wall assemblies based on wall type, drywall layers, insulation, stud spacing, resilient channel, and staggered studs.

Acoustics

Soundproofing Material Calculator

Calculate sound transmission loss using the mass law (TL = 20×log10(f×m) - 47 dB). Supports single and multi-layer assemblies with air gaps.

More in Construction & Building Trades.