Combustion Safety Flashcards

What is the primary purpose of a combustion appliance zone (CAZ) depressurization test?

Answer: To determine if the zone becomes sufficiently depressurized to cause backdrafting

The CAZ depressurization test identifies whether the appliance zone can be depressurized enough under worst-case conditions to cause combustion gases to backdraft into the living space.

Which of the following conditions represents a 'worst-case' scenario during a CAZ depressurization test?

Answer: All windows and doors closed, all exhaust fans on

Worst-case depressurization occurs when all windows and doors are closed and all exhaust fans, including range hoods and bath fans, are running simultaneously.

A atmospherically vented water heater fails a steady-state spillage test. What does this indicate?

Answer: Combustion gases are spilling from the draft hood into the living space

Steady-state spillage means the appliance is continuously venting combustion products into the conditioned space rather than up the flue, creating a CO hazard.

What CO concentration threshold (ppm) in undiluted flue gases typically triggers a 'fail' rating during a HERS combustion safety inspection?

Answer: 400 ppm

RESNET/BPI protocols generally flag undiluted flue gas CO readings above 400 ppm as a failure requiring investigation and remediation.

Which diagnostic tool is most appropriate for detecting combustion gas spillage at a draft hood?

Answer: Combustion analyzer or smoke pencil

A combustion analyzer measures CO and other gases directly, while a smoke pencil visually confirms airflow direction at the draft hood to detect spillage.

A sealed-combustion furnace draws combustion air directly from outside. How does this affect CAZ depressurization concerns?

Answer: It eliminates CAZ depressurization risk for that appliance since it does not use zone air

Sealed-combustion (direct-vent) appliances draw combustion air from outside and exhaust directly outside, so they are unaffected by CAZ pressure and do not contribute to backdrafting concerns.

What is the purpose of a draft pressure test on a natural-draft appliance flue?

Answer: To verify the flue is creating adequate negative pressure to remove combustion gases

Draft pressure testing verifies that the flue system is generating enough negative pressure (draft) to reliably pull combustion gases upward and out of the building.

When testing for ambient CO in a home, what is the BPI/RESNET action level (ppm) that requires immediate evacuation?

Answer: 35+ ppm sustained or any reading above 70 ppm

BPI protocols call for immediate evacuation when ambient CO exceeds 35 ppm sustained or any single reading exceeds 70 ppm, and HVAC systems should be shut down.

Which type of venting system uses a fan to push or pull combustion gases through the flue, making it less susceptible to backdrafting?

Answer: Power-vented or induced-draft venting

Power-vented and induced-draft appliances use a mechanical fan to move flue gases, providing positive pressure in the flue and reducing the risk of backdrafting from house depressurization.

A natural-draft gas furnace shares a masonry chimney with a wood-burning fireplace. What combustion safety concern does this create?

Answer: Simultaneous use can cause the furnace flue gases to backdraft into the home

When a fireplace draws combustion air from the chimney, it can depressurize the shared flue and reverse the flow of furnace exhaust gases back into the living space.

What does the term 'orphaned water heater' mean in the context of combustion safety?

Answer: A water heater left alone on an oversized flue after a furnace is replaced with a high-efficiency model

When a high-efficiency furnace no longer vents through a masonry chimney, the remaining atmospheric water heater may be 'orphaned' on an oversized flue, leading to condensation and draft problems.

Which condition would most likely cause a natural-draft appliance to backdraft even without house depressurization?

Answer: A flue that is too short or has an obstruction

A blocked or undersized flue creates resistance that prevents adequate draft, causing combustion gases to spill back into the space even when the house is at neutral pressure.

During a combustion safety test, you measure -7 Pa in the CAZ with all exhaust fans running and the largest window open. What does this result indicate?

Answer: The CAZ is dangerously depressurized and requires remediation

A CAZ depressurization of -7 Pa exceeds the BPI failure threshold (typically -5 Pa for atmospherically vented appliances), indicating a risk of backdrafting that requires correction.

What is the function of a draft hood on an atmospherically vented gas appliance?

Answer: It dilutes flue gases with room air and protects the burner from downdrafts

A draft hood allows room air to dilute flue gases and protects the burner flame from being extinguished by downdrafts or fluctuating chimney draft.

A HERS rater tests a home with a gas range and finds elevated CO in the kitchen. What is the most likely cause if only the range top burners are running normally?

Answer: Incomplete combustion at the range burner due to improper air-fuel mixture or dirty burner

Gas range burners with improper air-fuel ratios or partially blocked burner ports produce elevated CO due to incomplete combustion even during normal operation.

Which of the following best describes the hazard of a cracked heat exchanger in a forced-air gas furnace?

Answer: Combustion gases including CO can mix with and be distributed through supply air throughout the home

A cracked heat exchanger allows combustion gases to cross into the supply airstream, distributing CO and other combustion byproducts to every room served by the duct system.

What safety device is required by most codes in sleeping areas and on each level of a home to protect against CO poisoning?

Answer: CO alarm

CO alarms are required on each level of a home and outside sleeping areas to provide early warning of dangerous CO concentrations from combustion appliances.

During a worst-case CAZ test, which exhaust device typically contributes the most depressurization?

Answer: Range hood (400+ CFM)

Large range hoods with high CFM ratings typically dominate CAZ depressurization because they exhaust far more air than bathroom fans or dryers.

A home has been air-sealed and tightened significantly. What combustion safety issue may arise if no other changes were made?

Answer: Reduced infiltration may starve atmospheric appliances of combustion air, increasing backdrafting risk

Air sealing reduces the infiltration that previously supplied combustion air to atmospheric appliances, potentially increasing depressurization and backdrafting risk.

What is the correct procedure if a HERS rater discovers steady-state CO spillage from a water heater draft hood during testing?

Answer: Immediately shut down the appliance and advise the homeowner not to use it until repaired

Steady-state spillage is an immediate health and safety hazard; the appliance must be shut down and the homeowner advised not to use it until a qualified technician performs repairs.