NSS Combustion and Venting Systems 3

Question 1

What CO2 percentage in flue gas indicates normal combustion for a Navien natural gas appliance?

Accepted Answer

8 to 9 percent

Answer

3 to 4 percent

Answer

12 to 13 percent

Answer

15 to 16 percent

Question 2

What does visible white vapor puffing from a Navien vent termination during cold weather indicate?

Accepted Answer

Normal water vapor condensation from condensing operation

Answer

Incomplete combustion requiring immediate service

Answer

A cracked heat exchanger allowing water into the flue

Answer

Excessive CO production requiring immediate shutdown

Question 3

What is the primary function of the premix burner system used in Navien condensing units?

Accepted Answer

Mixes gas and air in precise ratios before ignition for efficient, low-emission combustion

Answer

Burns fuel at atmospheric pressure without pre-mixing for simplicity

Answer

Uses only recirculated flue gases to reduce emissions

Answer

Operates exclusively on liquefied petroleum gas configurations

Question 4

Which Navien model series is specifically designed as a condensing hydronic boiler for space heating applications?

Accepted Answer

NHB series

Answer

NPE series

Answer

NCB series

Answer

NPN series

Question 5

What CO level measured air-free in flue gas indicates acceptable combustion performance for a Navien unit?

Accepted Answer

Less than 200 ppm

Answer

200 to 600 ppm

Answer

600 to 1,000 ppm

Answer

Greater than 1,000 ppm

Question 6

What must a technician verify regarding combustion air when a Navien direct-vent unit is installed in a confined mechanical room?

Accepted Answer

That the unit draws all combustion air from outside through its sealed intake pipe

Answer

That the room has two louvered openings for natural air infiltration

Answer

That the room volume meets the 50 cubic feet per 1,000 BTU requirement

Answer

That a powered makeup air fan is installed and operational

Question 7

What must be done with condensate produced by a Navien condensing unit before it is discharged to a sanitary drain in many jurisdictions?

Accepted Answer

It must be passed through a condensate neutralizer before draining

Answer

It can be discharged directly to any drain without treatment

Answer

It must be collected and disposed of as regulated hazardous waste

Answer

It must be diluted with tap water at a 10:1 ratio before draining