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Duct Systems — ICC M1 Practice Questions

10 questions · 8% of the ICC M1 exam

Worked questions

1. A duct exercise specifies a friction rate of 0.15 inch of water column per 100 feet and an equivalent length of 75 feet, already including fittings. What pressure loss does this segment contribute at that rate?

  • A0.1500 inch of water column
  • B0.2000 inch of water column
  • 0.1125 inch of water column
  • D11.2500 inches of water column

Where to look it up

Explicit exercise assumptions; not a universal code requirement.

Why C is correct

Pressure loss = 0.15 Ă— 75/100 = 0.1125 inch of water column. This is an assigned design rate, not a universal IRC limit; equivalent length already includes fittings, so do not add them again.

2. For a duct-design calculation, the pressure available for duct friction is 0.30 inch of water column after all other component losses have been deducted. The controlling supply-and-return path has a total equivalent length of 200 feet, including fittings. Using friction rate = available pressure Ă— 100 / total equivalent length, what rate results?

  • A0.10 inch of water column per 100 feet
  • 0.15 inch of water column per 100 feet
  • C0.30 inch of water column per 100 feet
  • D0.60 inch of water column per 100 feet

Where to look it up

Explicit exercise assumptions; not a universal code requirement.

Why B is correct

Apply the supplied relation: 0.30 Ă— 100/200 = 0.15 inch of water column per 100 feet. Use the stated complete path and remaining pressure, not just the straight supply-run length. This exercise does not establish a universal code maximum.

3. A new dwelling has 6-inch-diameter round supply and return ducts for its forced-air heating and cooling system running through an unconditioned attic, outside the building thermal envelope. The ducts are not buried in ceiling insulation and do not qualify as being inside conditioned space. When checking the duct insulation alone under the 2024 IECC residential provision for ductwork outside conditioned space, what minimum insulation R-value applies to these ducts?

  • R-8 for both supply and return ducts
  • BR-6 for both supply and return ducts
  • CR-8 for supply ducts and R-3 for return ducts
  • DR-13 for both supply and return ducts

Where to look it up

https://dos.ny.gov/nys-energy-conservation-construction-code-noa-7242025

Why A is correct

Both ducts require at least R-8: the outside-conditioned-space rule applies the same diameter threshold to supply and return ductwork. These 6-inch ducts are in the 3-inch-and-larger group. Ductwork smaller than 3 inches instead has an R-6 minimum under this provision; there is no R-3 return-duct allowance here. This checks duct insulation only, not every energy or mechanical requirement. Source: 2024 IECC residential R403.3.3, reproduced without a New York modification in the official 2025 ECCCNYS, printed page 259 (PDF page 262). The separate New York duct-location amendment is not applied to this model-code question. https://dos.ny.gov/nys-energy-conservation-construction-code-noa-7242025

4. A bedroom supply-air exercise specifies 100 cubic feet per minute and an average duct velocity of 500 feet per minute. Using Q = velocity Ă— area, what internal cross-sectional area is required for this airflow calculation?

  • 0.20 square foot
  • B5.00 square feet
  • C50.00 square feet
  • D0.02 square foot

Where to look it up

Explicit exercise assumptions; not a universal code requirement.

Why A is correct

Area = 100/500 = 0.20 square foot. The bedroom label does not establish a universal duct diameter. Actual selection also requires the pressure-loss design and installation constraints; this question evaluates the supplied airflow relation only.

5. Under 2024 IRC M1601.4.1 (May 2024 printing), pressure-sensitive tape is proposed to seal joints in a flexible air duct. Which requirement applies?

  • The tape must comply with UL 181B and carry the 181B-FX marking, and the closure must be installed according to its manufacturer’s instructions
  • BAny tape is acceptable if it is wide enough to cover the joint
  • CFoil appearance alone establishes compliance
  • DMastic is the only permitted closure, so listed pressure-sensitive tape is prohibited

Where to look it up

https://codes.iccsafe.org/content/IRC2024P2/chapter-16-duct-systems

Why A is correct

M1601.4.1 permits multiple closure types. For tape on metallic or flexible air ducts and flexible air connectors, the section requires UL 181B compliance and the 181B-FX marking for pressure-sensitive tape. Closure systems follow their manufacturers’ instructions. The proposed listed tape is not prohibited merely because it is not mastic. A generic tape description or foil finish is insufficient. M1503 concerns cooking exhaust equipment and is not the general HVAC sealing rule. Source: https://codes.iccsafe.org/content/IRC2024P2/chapter-16-duct-systems

6. For a factory-made air duct listed to UL 181, what determines the support requirements under 2024 IRC M1601.4.4 (May 2024 printing)?

  • AA universal 4-foot interval for every duct material
  • BA universal 6-foot interval for every duct material
  • The duct manufacturer’s installation instructions
  • DA universal 10-foot interval for every duct material

Where to look it up

https://codes.iccsafe.org/content/IRC2024P2/chapter-16-duct-systems

Why C is correct

M1601.4.4 directs support of UL 181-listed factory-made ducts to the manufacturer’s installation instructions. It separately directs field- and shop-fabricated fibrous-glass ducts to the named SMACNA or NAIMA standard, and field- and shop-fabricated metal and flexible ducts to the named SMACNA metal-and-flexible standard. It does not prescribe the former question’s blanket 8-foot interval. The product category must be known before selecting a support rule. Source: https://codes.iccsafe.org/content/IRC2024P2/chapter-16-duct-systems

7. Reduced airflow has been measured at the registers served by one duct branch. The filter and blower operation have already been checked and are satisfactory. Which next step most directly investigates a problem in that branch before replacing equipment?

  • ACheck the air filter.
  • Inspect the ductwork for leaks and obstructions.
  • CMeasure the airflow at the registers.
  • DReplace the furnace fan motor.

Where to look it up

https://www.energy.gov/sites/default/files/2013/11/f5/hvac_guide.pdf

Why B is correct

Inspect the affected branch for disconnected joints, leakage, crushed sections or other obstructions, then use appropriate airflow or leakage measurements to confirm the fault. The question already establishes that the filter and blower were checked and reduced register flow measured. Replacing the fan motor before finding evidence of a motor fault is not justified. This is a diagnostic scenario, not a universal first-step sequence prescribed by the IRC. Source: https://www.energy.gov/sites/default/files/2013/11/f5/hvac_guide.pdf

8. A basement in an existing house is being converted into a living room under the 2024 IRC. The general ceiling meets its required height, but a supply duct projects below it. Under the duct-obstruction exception in R313.1.2, what is the minimum clear height from the finished floor below that duct?

  • A6 feet
  • 6 feet 4 inches
  • C7 feet
  • D8 feet

Where to look it up

https://dos.ny.gov/nys-residential-code-noa-7242025

Why B is correct

For habitable space created in the basement of an existing building, the stated exception permits ducts and other listed obstructions down to a minimum clear height of 6 feet 4 inches. This does not make that the general ceiling height for the whole living room or establish a universal 8-foot duct height. Apply the existing-basement conditions rather than a different room or building case. Source: 2024 IRC R313.1.2, Exception 2, reproduced without a substantive state modifier in the official 2025 RCNYS (2024 IRC base). https://dos.ny.gov/nys-residential-code-noa-7242025

2 more in the bank

Answers and explanations for these are in the app.

  • A residential building is being constructed with a forced-air heating and cooling system. During the inspection, you notice that the supply ducts are designed to deliver air at a velocity of 1500 fpm. What is the minimum diameter required for the supply ducts according to the 2024 International Residential Code?
  • You are inspecting the ductwork in an existing residential building and notice that the return ducts are located in the attic. How should you address the presence of insulation around the return ducts according to the 2024 International Residential Code?

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