These 5 questions cover furnaces, boilers, heat exchangers, venting and combustion air. On the National Home Inspector Examination they fall under Property Inspection (70% of the exam). Try each one before you open the answer: the explanation matters more than the letter.
1. The inspector operates a furnace on a 20°F day and the living room reaches only 58°F after an extended run. This observation suggests the system
- is operating normally for the outdoor temperature
- needs its thermostat recalibrated
- is oversized for the house
- may be unable to maintain the 68°F standard for habitable rooms
Show answer
Answer: D. may be unable to maintain the 68°F standard for habitable rooms
Heating systems are expected to maintain about 68°F in habitable rooms under design conditions. A system that cannot approach that under normal operation may be undersized, failing, or losing heat through distribution defects; the inspector reports the observation and recommends evaluation.
Memory tip: 68 is the target.
2. A sealed-combustion gas furnace draws its combustion air through a PVC pipe from outdoors and vents through a second PVC pipe. This appliance is BEST described as
- a natural draft appliance
- a direct exhaust appliance
- a direct vent appliance
- an unvented appliance
Show answer
Answer: C. a direct vent appliance
Direct vent appliances take combustion air from outdoors and discharge products outdoors through sealed piping, isolating combustion from house air. Direct exhaust appliances use house air for combustion but vent outdoors; natural draft units rely on buoyancy through a chimney.
Memory tip: Two pipes outside = direct vent.
3. An older gas furnace vents through a masonry chimney with no fan assisting the flue gases. This vent system relies on
- natural draft from the buoyancy of hot gases
- induced draft from a fan at the termination
- forced draft from a fan at the appliance
- power venting through the sidewall
Show answer
Answer: A. natural draft from the buoyancy of hot gases
Natural draft venting depends on hot combustion gases being lighter than surrounding air and rising on their own. It requires proper vent sizing, height, and warm flue conditions; cold chimneys and poor sizing cause spillage.
Memory tip: No fan = natural draft.
4. A gas furnace has a blower at the burner that pushes combustion gases through the vent. This venting arrangement is called
- natural draft
- forced draft
- induced draft
- gravity venting
Show answer
Answer: B. forced draft
Forced draft places the fan at the beginning of the vent system, pressurizing it. Induced draft places the fan downstream, pulling gases through. Forced-draft vents are under positive pressure and require sealed, listed vent materials.
Memory tip: Forced pushes; induced pulls.
5. A home is heated by a boiler that circulates hot water through baseboard units. During inspection, the inspector should operate the system and observe
- circulation, warm baseboards, and no leaks at piping
- the temperature rise across the heat exchanger
- the refrigerant line temperatures at the unit
- the static pressure in the supply ducts
Show answer
Answer: A. circulation, warm baseboards, and no leaks at piping
Hydronic systems distribute heat through piping rather than ducts. Inspection involves operating the boiler by normal controls, confirming circulation and heat at the terminal units, and checking for leaks, corrosion, relief valve discharge, and expansion tank condition.
Memory tip: Hydronic: water moves, check for leaks.