NATE Air Distribution 2 — Questions and Answers
Question 1: What unit is used to measure duct air leakage during a duct leakage test?
- Inches WC
- CFM25 (cubic feet per minute at 25 pascals) (Correct answer)
- Grains per pound
- MERV rating
Correct answer: CFM25 (cubic feet per minute at 25 pascals)
Duct leakage is expressed as CFM25, the airflow escaping through duct leaks when pressurized to 25 pascals above atmospheric pressure.
Question 2: What is the recommended duct sealing material for permanent duct repairs?
- Standard gray cloth duct tape
- Mastic sealant or metal foil tape (UL 181 listed) (Correct answer)
- Spray foam insulation
- Silicone caulk
Correct answer: Mastic sealant or metal foil tape (UL 181 listed)
Mastic sealant and UL 181 listed foil tape are durable, code-approved methods; standard cloth duct tape dries out and fails over time.
Question 3: What MERV rating range is recommended for residential HVAC filters to balance filtration and airflow?
- 1–4
- 5–8 (Correct answer)
- 9–13
- 14–16
Correct answer: 5–8
MERV 5–8 filters provide adequate filtration for residential equipment while maintaining sufficient airflow and avoiding excessive pressure drop.
Question 4: What is the purpose of a plenum in an HVAC duct system?
- Filter combustion gases from the airstream
- Serve as a pressure chamber that distributes or collects air from multiple duct branches (Correct answer)
- House the thermostat sensing element
- Provide combustion air to the furnace
Correct answer: Serve as a pressure chamber that distributes or collects air from multiple duct branches
The supply plenum distributes conditioned air from the air handler to multiple duct branches; the return plenum collects air from return branches.
Question 5: What is the maximum recommended duct velocity for residential supply ducts to minimize noise?
- 400–600 FPM
- 700–900 FPM (Correct answer)
- 1,200–1,500 FPM
- 2,000+ FPM
Correct answer: 700–900 FPM
Residential supply ducts typically target 700–900 FPM to balance duct size with acceptable noise levels.
Question 6: What is the effect of duct leakage in unconditioned spaces like attics and crawlspaces?
- Slightly increases equipment run time
- Wastes significant conditioned air to outside, dramatically increasing energy consumption and reducing comfort (Correct answer)
- Has negligible effect on system performance
- Only affects humidity levels
Correct answer: Wastes significant conditioned air to outside, dramatically increasing energy consumption and reducing comfort
Leaking supply ducts in unconditioned spaces lose conditioned air to outside while leaking return ducts pull hot/cold unconditioned air into the system.
NATE Air Distribution 2
What unit is used to measure duct air leakage during a duct leakage test?