NATE Air Distribution 1 — Questions and Answers
Question 1: What does external static pressure (ESP) measure in an HVAC duct system?
- Velocity of air at the supply registers
- Total resistance to airflow the blower must overcome, measured in inches of water column (Correct answer)
- Duct leakage to outside
- Return air CO2 concentration
Correct answer: Total resistance to airflow the blower must overcome, measured in inches of water column
ESP is the sum of supply and return static pressures and indicates how hard the blower works against the duct system resistance.
Question 2: What tool is used to measure air velocity in a duct or at a register?
- Manometer
- Anemometer or flow hood (Correct answer)
- Psychrometer
- Combustion analyzer
Correct answer: Anemometer or flow hood
An anemometer measures air velocity in feet per minute (FPM); a flow hood captures total CFM at a register directly.
Question 3: What is Manual J used for in residential HVAC design?
- Duct sizing calculations
- Calculating heating and cooling loads for a structure (Correct answer)
- Selecting refrigerant type
- Sizing expansion valves
Correct answer: Calculating heating and cooling loads for a structure
ACCA Manual J is the industry-standard load calculation procedure that determines the BTU capacity required to heat and cool a home.
Question 4: What is the purpose of a balancing damper in a duct branch?
- Prevent backdrafting
- Adjust airflow to individual zones to balance the system and deliver correct CFM to each room (Correct answer)
- Filter particulates from the airstream
- Reduce duct noise
Correct answer: Adjust airflow to individual zones to balance the system and deliver correct CFM to each room
Balancing dampers restrict airflow in over-supplied branches, diverting more air to under-supplied areas for proper room-by-room comfort.
Question 5: What condition does a very high return static pressure typically indicate?
- Oversized ductwork
- Restricted return airflow due to clogged filter, blocked return grilles, or undersized return duct (Correct answer)
- Excessive supply air
- Refrigerant overcharge
Correct answer: Restricted return airflow due to clogged filter, blocked return grilles, or undersized return duct
High return static pressure means the system is starved for return air, which reduces airflow and increases strain on the blower.
Question 6: What does ACCA Manual D provide for HVAC installations?
- Equipment selection guidelines
- Procedures for residential duct system design and sizing (Correct answer)
- Commissioning and startup procedures
- Indoor air quality standards
Correct answer: Procedures for residential duct system design and sizing
Manual D provides the calculations and procedures for designing duct systems that deliver the correct airflow to each room based on Manual J loads.
NATE Air Distribution 1
What does external static pressure (ESP) measure in an HVAC duct system?