NSS Combustion and Venting Systems 1 — Questions and Answers
Question 1: What vent pipe material is approved for use with Navien condensing tankless water heaters?
- Type B gas vent
- PVC/CPVC Schedule 40 (Correct answer)
- Galvanized steel
- Type L vent pipe
Correct answer: PVC/CPVC Schedule 40
Navien condensing units are Category IV appliances requiring PVC or CPVC vent pipe rated to handle acidic condensate and the temperatures of condensing exhaust.
Question 2: What venting category classification applies to Navien condensing units?
- Category I
- Category II
- Category III
- Category IV (Correct answer)
Correct answer: Category IV
Category IV appliances operate with positive vent pressure and produce flue gases below the dew point, requiring corrosion-resistant, pressure-tight vent systems like PVC.
Question 3: What is the minimum required clearance between a Navien vent termination and an operable window or door?
- 6 inches
- 12 inches (Correct answer)
- 18 inches
- 4 feet
Correct answer: 12 inches
A minimum of 12 inches clearance from operable windows, doors, and gravity air intakes is required per Navien installation guidelines to prevent combustion products from re-entering the structure.
Question 4: In a concentric (coaxial) vent system on a Navien unit, which pipe carries the exhaust gases?
- The outer pipe
- The inner pipe (Correct answer)
- Both pipes share exhaust equally
- It alternates based on demand
Correct answer: The inner pipe
In a concentric vent system, the inner pipe carries hot exhaust gases to the outside while the outer pipe draws fresh combustion air into the unit.
Question 5: What is the required slope for horizontal vent pipe runs on a Navien condensing unit?
- Level with no slope
- 1/4 inch per foot upward toward the termination
- 1/4 inch per foot back toward the unit (Correct answer)
- 1/2 inch per foot toward the termination
Correct answer: 1/4 inch per foot back toward the unit
Horizontal vent runs must slope back toward the unit at 1/4 inch per foot so acidic condensate drains to the unit's condensate trap rather than pooling in the pipe.
Question 6: Which of the following is NOT an acceptable Navien vent termination location?
- Through an exterior wall
- Through the roof
- Directly into an unlined masonry chimney (Correct answer)
- Under a soffit with proper clearances
Correct answer: Directly into an unlined masonry chimney
Navien condensing units must not vent directly into unlined masonry chimneys because acidic condensate would deteriorate the masonry; a dedicated corrosion-resistant liner is required.
Question 7: How many equivalent vent feet does a standard 90-degree elbow add to the total vent length calculation for Navien units?
- 2 feet
- 5 feet (Correct answer)
- 10 feet
- 15 feet
Correct answer: 5 feet
Per Navien installation guidelines, each 90-degree elbow adds 5 equivalent feet to the total calculated vent length, which must remain within the maximum allowable run.
NSS Combustion and Venting Systems 1
What vent pipe material is approved for use with Navien condensing tankless water heaters?