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

Natural gas appliances typically produce 8 to 9 percent CO2 in flue gas during normal stoichiometric combustion; values significantly outside this range indicate an air-to-fuel ratio issue.

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

Water vapor is a normal combustion byproduct of burning natural gas, and in cold weather it condenses into visible steam at the vent outlet — this is normal condensing appliance behavior.

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

Premix burners combine gas and combustion air in controlled ratios before the flame, resulting in more complete combustion, higher thermal efficiency, and lower NOx emissions.

Question 4

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

Accepted Answer

NHB series

Answer

The NHB (Navien Hydronic Boiler) series is purpose-built for space heating applications using hot water hydronic distribution systems such as radiant floor or baseboard heating.

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

Flue gas CO levels below 200 ppm air-free indicate sufficiently complete combustion; higher values suggest incomplete combustion that may require burner adjustment or heat exchanger inspection.

(NSS) Certified Navien Service Specialists Practice Test

(NSS) Certified Navien Service Specialists Practice Test

NSS Combustion and Venting Systems 3