21 HVAC, Insulation & Ventilation Practice Questions & Answers

1. 1. During a furnace inspection the inspector sees rust flakes on the burners, soot around the burner compartment, and a burner flame that shifts and turns yellow the moment the blower starts. What is the appropriate response?

   • A.Note that flame movement when the blower starts is normal air turbulence and requires no comment
   • B.Shut the gas off at the meter and tag the appliance out of service, because a cracked heat exchanger has been confirmed
   • C.Remove the heat exchanger panels and inspect the exchanger internally with a mirror and light to confirm the crack
   • D.Report the observed conditions as indicators of possible heat exchanger failure, explain the safety significance, and recommend evaluation by a qualified heating contractor✓ Answer

   When the blower runs it pressurizes the air side of the cabinet, and air escaping through a breach in the heat exchanger disturbs the flame and makes it burn yellow; rust flakes and soot are the same family of evidence. A visual look at readily accessible surfaces can never rule a heat exchanger in or out, and a home inspection is visual and non-invasive, so dismantling the appliance, operating shut-off valves or declaring a diagnosis all exceed the inspector's role. The correct output is a description of what was seen, why it matters for carbon monoxide safety, and a referral to a qualified specialist.

   Source: National Home Inspector Examination content outline — heating systems and combustion safety; home inspection standards of practice, scope and limitationsReport a problem with this question

2. 2. Scorching and melted wire insulation are visible on the outside of a gas furnace's burner compartment, and when the burners fire, flame briefly escapes forward out of the compartment opening. Which statement best describes this finding?

   • A.It indicates an over-firing gas valve that the inspector should adjust before continuing the inspection
   • B.It is a normal ignition characteristic of an older atmospheric burner and needs no comment
   • C.It indicates a failed thermostat heat anticipator that is causing the burners to light too quickly
   • D.It is flame rollout, which indicates that combustion gases cannot move freely through the heat exchanger or the vent, or that the burners are starved of combustion air; it is a fire and carbon monoxide hazard that warrants prompt evaluation✓ Answer

   Burner flames should be drawn back into the heat exchanger by the appliance's draft. If the exchanger passages or the vent are blocked, or if the room cannot supply enough combustion air, the products of combustion have nowhere to go and hot gases and flame push forward out of the burner opening, scorching the cabinet and nearby wiring. A rollout switch is intended to lock the appliance out when this happens, and the condition is reported as a safety hazard needing evaluation, not adjusted by the inspector.

   Source: National Home Inspector Examination content outline — heating systems, combustion by-products and burner safety devicesReport a problem with this question

3. 3. A high-efficiency condensing furnace has been installed and vented with plastic pipe through the rim joist, and it drains acidic condensate to a floor drain. The gas water heater that formerly shared the masonry chimney with the old furnace is now the only appliance connected to that flue, and spillage is detected at its draft hood several minutes after the burner fires. What best explains the spillage?

   • A.The water heater thermostat is set too low for the flue to establish draft
   • B.Condensate from the new furnace has flooded the water heater's burner compartment
   • C.The masonry flue is now far too large and too cold for the single small appliance left on it, so the flue gases cool, lose buoyancy and cannot establish draft — the classic orphaned water heater problem✓ Answer
   • D.The plastic furnace vent is pulling combustion air away from the water heater burner

   Draft in an atmospheric vent depends on hot, buoyant flue gases warming the flue and rising. A masonry chimney sized for a furnace plus a water heater has far more mass and cross-section than the water heater alone can heat, so the gases cool, slow and stall, and spillage appears at the draft hood along with condensation inside the chimney. Removing one appliance from a shared flue is a system-interaction change that must be re-evaluated, typically by relining the chimney to the correct size for the remaining appliance.

   Source: National Home Inspector Examination content outline — venting of fuel-fired appliances and inter-dependence of mechanical systemsReport a problem with this question

4. 4. A gas furnace and a gas water heater share a small, tightly finished basement closet with a solid weatherstripped door and no other openings. What is the principal concern the inspector should report?

   • A.A louvered door is needed only if the appliances are oil-fired rather than gas-fired
   • B.The confined space raises gas pressure at the burners, so the appliances will over-fire
   • C.The enclosed volume is too small to supply the combustion air these appliances need, so permanent openings connecting the closet to a large enough interior space or to the outdoors are required to prevent oxygen starvation, incomplete combustion and spillage✓ Answer
   • D.The only real concern is burner noise transmitted into the finished living space

   Whether a space is confined is judged by comparing its volume to the total input rating of all the appliances in it; a small sealed closet cannot hold enough air to support continuous combustion. As the burner consumes oxygen the flame degrades toward incomplete combustion, which produces carbon monoxide, and the falling pressure in the closet can reverse the vent so flue gases spill back into the room. The remedy in principle is a dependable supply of air from outside the closet, provided by permanent high and low openings rather than by relying on the door being left ajar.

   Source: National Home Inspector Examination content outline — combustion air supply for fuel-fired appliances in confined spacesReport a problem with this question

5. 5. A hot water boiler's pressure-temperature relief valve drips every time the system heats up, the pressure gauge climbs well above its cold reading during each firing cycle, and the steel expansion tank above the boiler feels equally hot along its entire length. Which explanation is most consistent with these observations?

   • A.The relief valve is oversized for the boiler and should be replaced with a smaller one
   • B.The circulator pump is running backwards and is pushing water out through the relief valve
   • C.The aquastat low-limit setting is too low, which drives pressure up during each cycle
   • D.The expansion tank has become waterlogged and lost its air cushion, so heated water has nowhere to expand and system pressure rises until the relief valve opens✓ Answer

   Water is essentially incompressible, so a closed hydronic loop needs a trapped volume of air to absorb the expansion that occurs as the water heats. When an old steel compression tank loses that air, usually because the air is absorbed into the water, the tank fills and the whole tank warms uniformly instead of staying cool at the bottom; pressure then spikes on every cycle and the relief valve opens as designed. The relief valve is behaving correctly and is a symptom, not the defect, so the inspector reports the repeated discharge and recommends correction of the expansion control.

   Source: National Home Inspector Examination content outline — hydronic heating systems, expansion control and relief devicesReport a problem with this question

6. 6. In January a client complains that the air from the registers of an electric heat pump feels cool, and during the inspection the outdoor unit periodically stops, makes a whooshing sound and releases a cloud of vapour while the outdoor fan is off. How should the inspector interpret these two observations?

   • A.The cool air proves the charge is low, and the inspector should attach gauges to verify it
   • B.The vapour indicates a refrigerant leak and the system should be shut down immediately
   • C.Both are normal: heat-pump supply air is delivered well below body temperature so it feels cool to the hand, and the vapour is the normal defrost cycle melting frost off the outdoor coil✓ Answer
   • D.Both are defects: the reversing valve has failed and the outdoor unit is overheating

   A heat pump moves heat rather than burning fuel, so it delivers a larger volume of moderately warm air instead of the hot air a furnace produces; because that supply temperature is below skin temperature it feels cool even though the house is being heated. During defrost the unit briefly reverses to cooling with the outdoor fan stopped so the hot refrigerant melts frost from the outdoor coil, and the visible plume is that melted frost evaporating. Verifying refrigerant charge with gauges is outside the scope of a visual home inspection.

   Source: National Home Inspector Examination content outline — heat pump operation, defrost cycle and inspection limitationsReport a problem with this question

7. 7. A gas furnace's igniter glows, the burners light normally, and then the flame goes out after a few seconds; after three attempts the control board locks the appliance out. Which control is most likely responsible for shutting off the gas, and what does that control protect against?

   • A.The pressure switch, which proves the draft inducer is moving air before ignition is allowed to begin
   • B.The thermostat, which stops calling for heat as soon as the flame is established
   • C.The high-limit switch, which protects the equipment from overheating when airflow through the furnace is restricted
   • D.The flame-sensing device, which must prove that flame is actually present or the control closes the gas valve to keep raw gas from filling the combustion chamber✓ Answer

   The sequence described — successful ignition followed by loss of flame a few seconds later and then lockout — is the signature of a flame-proving failure: the sensing rod or thermocouple is not confirming flame to the control, so the control closes the gas valve on purpose. That interlock exists to prevent unburned gas from accumulating in the combustion chamber. The other three controls do different jobs: the limit protects against overheating from restricted airflow, the pressure switch confirms inducer airflow before ignition, and the thermostat simply starts and stops the call for heat.

   Source: National Home Inspector Examination content outline — heating system controls and safety interlocksReport a problem with this question

8. 8. The inspection takes place after a week in which the outdoor temperature has stayed in the low 40s F. The client asks the inspector to run the central air conditioning to prove that it works. What is the correct course of action?

   • A.Set the thermostat to its lowest setting for at least fifteen minutes first so that the compressor warms up
   • B.Energize the outdoor unit directly at the disconnect, bypassing the thermostat
   • C.Run the system briefly at the thermostat, since a short test cannot damage the equipment
   • D.Decline to operate the cooling equipment because starting a compressor in cold conditions risks damage from liquid refrigerant and thickened oil, and report that the system was not operated and the reason why✓ Answer

   When the outdoor unit has been cold for an extended period, refrigerant migrates to and condenses in the compressor crankcase and the lubricating oil becomes thick, so an immediate start can slug the compressor with liquid and run it with poor lubrication. Standards of practice consistently direct the inspector not to operate equipment when doing so could damage it, and to state clearly in the report which systems were not inspected or operated and why. Bypassing the thermostat at the disconnect is also outside the visual, non-invasive scope of the inspection.

   Source: Home inspection standards of practice — operating conditions, equipment protection and reporting of items not inspectedReport a problem with this question

9. 9. An inspector wants a simple screening check of whether an operating central air conditioner is cooling as it should. Which description of the temperature-split method is correct?

   • A.Measure the suction line and liquid line temperatures at the outdoor unit and compare the difference to a refrigerant charging chart
   • B.After the system has run long enough to stabilize, measure the air temperature in the return near the equipment and at a supply register or plenum, and compare the difference to the range the manufacturer expects, treating a result outside that range as a reason to recommend further evaluation✓ Answer
   • C.Measure the outdoor air temperature and subtract the temperature of the liquid line at the condenser
   • D.Measure the air leaving the outdoor coil and compare it to the room thermostat reading

   The temperature split compares the air entering the evaporator with the air leaving it, so both readings must be taken in the airstream close to the equipment after the system has stabilized. It is a screening tool, not a measurement of charge: a smaller than expected split can come from low charge, a restricted metering device or too much airflow, while a larger than expected split usually points to restricted airflow such as a loaded filter or dirty coil. Because determining refrigerant charge requires gauges and is beyond a visual inspection, an out-of-range result is reported as a reason for evaluation by a qualified contractor.

   Source: National Home Inspector Examination content outline — cooling system inspection methods and measurement techniquesReport a problem with this question

10. 10. In mid-summer an inspector finds the larger insulated refrigerant line frosted back toward the outdoor unit, a block of ice on the evaporator coil, and very little air coming from the supply registers. Which combination of likely causes and correct action should the report reflect?

    • A.A failed condensate trap; recommend clearing the drain line and returning the system to service
    • B.A failed thermostat heat anticipator; recommend replacing the thermostat
    • C.Either restricted airflow across the evaporator — a loaded filter, closed or blocked returns, or a fouled coil — or a low refrigerant charge, both of which drive the coil surface below freezing so condensate turns to ice; report the condition and recommend evaluation and service by a qualified contractor✓ Answer
    • D.Only an oversized condenser; recommend replacing the outdoor unit

    An evaporator ices when its surface falls below freezing, and there are two common routes to that: too little warm air passing over the coil to keep it above freezing, or too little refrigerant so the remaining refrigerant boils at a lower pressure and temperature. Icing is self-reinforcing because the ice further blocks airflow, and frost carried back along the suction line signals liquid refrigerant reaching the compressor. Distinguishing charge problems from airflow problems requires gauges and service work, so the inspector documents the observation and its significance and defers diagnosis to a qualified contractor.

    Source: National Home Inspector Examination content outline — refrigerant cycle principles, cooling system defects and inspection limitationsReport a problem with this question

11. 11. An air handler sits in an attic above a finished ceiling. Water is dripping from the end of a separate small pipe that discharges above an exterior window, and there is standing water in the pan beneath the unit. What is the best interpretation of these findings?

    • A.The auxiliary drain is doing its job as a visible warning that the primary condensate drain is blocked; the blockage and the standing water should be reported for correction before the pan overflows into the ceiling✓ Answer
    • B.The pan is meant to hold water, so only the dripping pipe needs attention
    • C.The condensate pump has failed and the auxiliary pan has become the primary drain
    • D.The dripping pipe is itself the defect and simply needs to be rerouted so it does not discharge above a window

    Equipment installed above a finished space is given a second line of defence precisely because an overflow would damage the building: a secondary drain or an auxiliary pan with its own drain, often combined with a float switch that shuts the equipment down. The secondary line is deliberately terminated where someone will notice it, so water coming out of it is a warning that the primary drain has stopped working, not a plumbing mistake. Standing water in the pan confirms the primary path is blocked, and both conditions belong in the report as items needing correction.

    Source: National Home Inspector Examination content outline — condensate control and disposal for cooling and condensing appliancesReport a problem with this question

12. 12. Two houses have the same amount of duct leakage. In one house the ducts run through a vented attic; in the other they run inside a conditioned basement within the insulated envelope. Why is the attic leakage the more significant finding?

    • A.Leakage inside the envelope cannot occur once the joints are sealed with mastic
    • B.Attic ducts carry more air simply because they are closer to the equipment
    • C.Air lost from attic ducts leaves the thermal envelope entirely, and return-side leaks draw hot, dusty attic air into the system, while the resulting pressure imbalance can depressurize the house and encourage backdrafting; leakage inside the envelope largely stays within the heated and cooled space✓ Answer
    • D.Ducts installed in attics are always undersized, so any leakage matters more

    Duct leakage matters according to where the air goes and where the make-up air comes from. Supply leakage outside the thermal boundary is energy delivered to the attic, and return leakage outside the boundary pulls in attic air with its heat, dust and moisture while the house must draw replacement air through the shell. Unequal supply and return leakage also shifts house pressure, and a house pulled negative can spill flue gases from an atmospherically vented appliance, which turns a comfort and energy issue into a safety issue.

    Source: Residential building science — duct leakage, thermal boundary location and house pressure effectsReport a problem with this question

13. 13. An older converted gravity furnace has round ducts wrapped in a crumbling white fibrous material with a paper-like outer jacket, and similar material is packed at the plenum joints. What is the inspector's appropriate action?

    • A.Describe the material as a suspected asbestos-containing product in damaged condition, advise that it should not be disturbed, and recommend evaluation and testing by a qualified specialist✓ Answer
    • B.Collect a sample of the material so the client can have it tested
    • C.State in the report that the material is asbestos and must be removed by an abatement contractor before the sale closes
    • D.Repair the damaged sections with tape during the inspection so that fibres are contained

    Asbestos-containing materials cannot be identified visually; only laboratory analysis can confirm them, so the defensible report language is that the material is suspect and should be treated as such until tested. Damaged, friable insulation releases fibres when handled, which is why both sampling and taping are the wrong moves for a visual, non-invasive inspection. The inspector describes the material and its condition, notes that it should not be disturbed, and refers the client to a qualified specialist.

    Source: National Home Inspector Examination content outline — reporting suspected hazardous materials and inspection scope limitationsReport a problem with this question

14. 14. A bonus room over a garage is cold in winter and hot in summer. In the attic space behind the room the inspector finds fibreglass batts stuffed between the knee wall studs with nothing covering their attic side, the floor joist cavities under the room open to the attic at the base of the knee wall, and no insulation in the floor over the garage. Which statement best explains the performance problem?

    • A.The knee wall should have been built as a masonry wall to provide thermal mass
    • B.The room simply needs a larger supply register and a second return grille
    • C.The batts have the wrong colour of facing for that location
    • D.The thermal boundary and the air barrier are neither continuous nor aligned: attic air washes through the open floor cavities and around the uncovered batts, so the insulation cannot perform anywhere near its rated value✓ Answer

    Insulation only resists conduction; it does nothing about air moving through or around it. When the joist cavities under the floor are open at the knee wall, attic air flows straight beneath the finished floor, and when the batts have no sheathing or air barrier on their attic face, wind washing strips heat from the fibres. The fix in principle is to close and block the cavity ends, provide a continuous air barrier in contact with the insulation, and keep the thermal boundary aligned with it all the way around the room, including the floor over the unconditioned garage.

    Source: Residential building science — continuity and alignment of the thermal boundary and the air barrierReport a problem with this question

15. 15. In a heating-dominated climate, why is a vapour retarder normally placed toward the interior face of an insulated wall assembly, and what companion measure matters even more?

    • A.The retarder goes on the interior to reflect radiant heat back into the room, and adding a second retarder on the exterior improves the effect
    • B.Water vapour tends to move from the warm, humid side toward the cold, dry side, so the retarder goes toward the warm-in-winter side to keep vapour out of the cold sheathing; air sealing matters even more, because air leakage carries far more moisture into an assembly than diffusion does✓ Answer
    • C.The retarder belongs on the cold side of the assembly in every climate, and the companion measure is increasing attic ventilation
    • D.The retarder goes on the interior to stop liquid rainwater, and the companion measure is simply adding more insulation

    Vapour diffuses from higher to lower vapour pressure, which in winter means from the warm, humid interior toward the cold exterior; a retarder on the warm-in-winter side slows that drive before it reaches the cold sheathing where it could condense. The same logic explains why an interior low-permeance retarder is a liability in a hot, humid climate and why doubling up retarders on both faces traps moisture with no drying path. Building science also ranks air transport well ahead of diffusion as a moisture carrier, so sealing the air barrier does more to protect an assembly than the retarder itself.

    Source: Residential building science — vapour retarders, permeance classes and moisture transport mechanismsReport a problem with this question

16. 16. Blown insulation in an attic has been pushed out over the top plates until it fills the space at the eaves, no baffles are present, and the roof has a continuous ridge vent. What is the most likely consequence?

    • A.Nothing of consequence; insulation at the eaves improves performance and does not affect the vent path
    • B.Intake air at the soffits is blocked, so the eave-to-ridge ventilation path is broken; the ridge vent then draws its air from the house through ceiling bypasses, and in cold weather the result is moisture accumulating on the sheathing and a greater risk of ice damming at the eaves✓ Answer
    • C.The attic will simply be over-ventilated because the ridge vent now works on its own
    • D.The ridge vent will reverse and act as an intake, drying the attic more effectively

    Attic ventilation works as a path, not as a collection of holes: air must be able to enter low at the eaves and leave high at the ridge. When insulation buries the soffit openings, the exhaust opening still pulls, and the easiest remaining source of air is the warm, humid house below, leaking up through top plates, chases and light fixtures. That warm moist air condenses on cold sheathing and also warms the deck unevenly, which drives snowmelt toward the cold eaves where it refreezes; a baffle at each rafter bay preserves the air channel while still allowing full insulation depth over the top plate.

    Source: Residential building science — attic ventilation air path, insulation baffles and ice dam formationReport a problem with this question

17. 17. A house has a continuous ridge vent and also a thermostatically controlled powered attic ventilator mounted in the roof. Why is this combination a reportable concern?

    • A.The ridge vent will freeze shut whenever the fan runs
    • B.Powered ventilators may not be used on roofs covered with asphalt shingles
    • C.The fan and the ridge vent cancel each other electrically, so both stop working
    • D.The fan takes the easiest air available, which is the nearby ridge vent and the leaky ceiling below, so it short-circuits the intended eave-to-ridge path, pulls conditioned air out of the house, and can depressurize the attic enough to affect the draft of combustion appliances✓ Answer

    A powered ventilator creates a strong negative pressure in the attic and air follows the path of least resistance. The nearest large opening is usually the ridge vent itself, so the fan simply recirculates air past the ridge instead of drawing it up from the eaves, and whatever it cannot get through the roof it pulls through gaps in the ceiling plane, wasting heated or cooled air and dragging house humidity into the attic. In a house with atmospherically vented appliances, that added depressurization can also interfere with proper draft, which makes it a safety comment rather than only an efficiency comment.

    Source: National Home Inspector Examination content outline — attic ventilation systems and interaction with combustion appliance draftReport a problem with this question

18. 18. In a humid summer climate a vented crawlspace with an exposed earth floor shows water droplets on the cool ductwork and dampness on the underside of the subfloor, and the problem is worst on the hottest, most humid days. What mechanism explains this, and what alternative approach addresses it?

    • A.The soil is releasing heat that boils moisture out of the subfloor, and a radiant barrier is the remedy
    • B.Warm, humid outdoor air drawn in through the vents is cooled below its dew point by the cool crawlspace surfaces and condenses on them; a closed, conditioned crawlspace with a continuous sealed ground vapour retarder, insulated perimeter walls and a means of drying is the alternative approach✓ Answer
    • C.Rain is entering through the vents, and enlarging the vents will dry the space faster
    • D.The ductwork is leaking condensate from the cooling coil, and sealing the duct joints will stop it

    Ventilation only dries a space when the incoming air is drier than the air inside. In humid summer weather the outdoor air holds a great deal of moisture, and the crawlspace surfaces stay near the cooler ground temperature, so bringing that air in raises its relative humidity until it reaches dew point on ducts, piping and framing; more vent area makes the condensation worse rather than better. Closing the crawlspace, covering the soil with a sealed vapour retarder to stop evaporation from the ground, insulating the perimeter walls and providing conditioned air or a dehumidifier addresses the mechanism instead of feeding it.

    Source: Residential building science — crawlspace moisture control, ventilation versus encapsulationReport a problem with this question

19. 19. A bathroom exhaust fan discharges through a length of uninsulated flexible duct that ends loose in the attic near the ridge. In winter the inspector finds frost on the nail points and dark staining on the roof sheathing above. What is the correct assessment?

    • A.Discharging into a well-ventilated attic is acceptable as long as the roof has a ridge vent
    • B.Moist air from the bathroom is being dumped into the attic, where it condenses and freezes on the cold sheathing, wetting the wood and supporting mould growth and decay; the duct needs to be insulated and carried through to an outdoor termination✓ Answer
    • C.The frost is caused by roof leaks and is unrelated to the fan duct
    • D.The fan is undersized, and installing a larger fan will resolve the sheathing staining

    A bathroom fan concentrates the moisture generated by showering into a single stream of very humid air, and discharging that stream into an attic simply relocates the moisture to the coldest surface in the house. The vapour condenses and freezes on the sheathing and nail points, then melts and wets the wood repeatedly, which is the classic sequence behind sheathing staining, mould and eventual decay. Local exhaust must terminate outdoors, and the duct should be insulated and sloped so that condensate inside it cannot drain back into the fan housing and through the ceiling.

    Source: National Home Inspector Examination content outline — mechanical exhaust termination and moisture effects on building componentsReport a problem with this question

20. 20. A clothes dryer is connected to the wall outlet with a ribbed plastic accordion duct that is crushed behind the appliance, and lint is visible at the joints. Which statement best captures the defect?

    • A.The only issue is appearance, since lint at the joints is normal and harmless
    • B.The duct should be replaced with a screened termination so birds cannot enter the ribbed sections
    • C.The ribbed plastic duct traps lint, sags and crushes easily, and accumulated lint next to a heat source is highly combustible, so the exhaust should be smooth-walled rigid metal, run to an outdoor termination and kept clear of obstructions✓ Answer
    • D.The duct is acceptable as long as it is shorter than the manufacturer's stated limit

    Dryer exhaust carries lint, and every ridge, sag or crush point gives the lint somewhere to settle; once a duct is partly plugged the airflow drops, the dryer runs hotter and longer, and the accumulated lint sits in a warm airstream as ready fuel. Plastic and thin foil accordion duct add a combustible or easily damaged wall to that same path, which is why the exhaust should be smooth-walled rigid metal that resists crushing and sheds lint. Terminations are fitted with a backdraft damper and left unscreened, because a screen is exactly the sort of obstruction that collects lint.

    Source: National Home Inspector Examination content outline — clothes dryer exhaust materials, obstructions and fire hazardsReport a problem with this question

21. 21. After a kitchen renovation added a high-capacity ducted range hood, the homeowner reports a sooty smell, and the inspector observes flue gases spilling from the draft hood of the atmospherically vented gas water heater whenever the hood runs on high with the bathroom fans on. What best explains this?

    • A.The water heater's thermostat was disturbed during the renovation
    • B.The water heater is oversized for the house and should be replaced with a tankless model
    • C.The range hood duct has been connected into the water heater's vent
    • D.The exhaust appliances are depressurizing the house faster than replacement air can leak in, so the water heater's flue becomes the easiest path for make-up air and its draft reverses; make-up air for the hood and evaluation of the appliance venting are needed✓ Answer

    An atmospherically vented appliance relies on a very weak buoyancy-driven draft, so it is the first thing in the house to fail when exhaust fans pull the interior negative. A powerful range hood plus bath fans can move more air out than the building shell can replace, and the large, open flue then becomes a convenient inlet, reversing the flow and pushing combustion products into the living space. This is a carbon monoxide hazard warranting prompt attention, and the correction in principle is dedicated make-up air interlocked with the hood, along with evaluation of the appliance venting by a qualified contractor.

    Source: National Home Inspector Examination content outline — make-up air, house depressurization and inter-dependence of mechanical and ventilation systemsReport a problem with this question

Practice questions based on the National Home Inspector Examination content outline, widely shared home inspection standards of practice, and residential building science. Not affiliated with or endorsed by any examination board, licensing authority, or inspector association. A home inspection is a visual, non-invasive examination and is not a code-compliance inspection — nothing here should be read as a code requirement. Home inspection is regulated differently from place to place; confirm your own jurisdiction's requirements and the standards of practice you are held to before testing or inspecting. About the National Home Inspector Examination →