CMI CMI HVAC Systems & Ventilation Inspection 2 — Questions and Answers
Question 1: What is 'thermal bypassing' in duct systems and how does it contribute to mold growth?
- Unsealed duct connections allow warm humid air to contact cold duct surfaces, causing condensation and mold growth (Correct answer)
- Thermal bypassing refers to insulation that is too thick, blocking heat exchange
- It describes a situation where heated air skips certain rooms
- Thermal bypassing is a positive feature that improves energy efficiency
Correct answer: Unsealed duct connections allow warm humid air to contact cold duct surfaces, causing condensation and mold growth
When duct joints are not properly sealed, warm moist air infiltrates and contacts cold duct surfaces, resulting in condensation that supports mold colonization on duct liner and adjacent materials.
Question 2: Which ASHRAE standard provides ventilation rate recommendations that, when not met, can contribute to elevated indoor humidity and mold risk?
- ASHRAE 62.1 (Correct answer)
- ASHRAE 90.1
- ASHRAE 55
- ASHRAE 15
Correct answer: ASHRAE 62.1
ASHRAE Standard 62.1 specifies minimum ventilation rates for acceptable indoor air quality; inadequate ventilation allows moisture to accumulate, elevating mold risk.
Question 3: A mold inspector discovers mold growth on supply diffusers throughout a commercial building. What is the most likely underlying cause?
- The supply air is below the dew point of the room air, causing condensation on the diffuser surfaces (Correct answer)
- The diffusers are made of a material that supports mold growth regardless of moisture
- Mold spores have contaminated only the diffusers and not the ductwork
- High air velocity through diffusers prevents condensation
Correct answer: The supply air is below the dew point of the room air, causing condensation on the diffuser surfaces
When cold supply air exits diffusers into warm humid room air, the metal diffuser surface can drop below the dew point, creating condensation that supports mold growth.
Question 4: What indoor relative humidity range is recommended by the EPA to minimize mold growth in residential buildings?
- 30–50% (Correct answer)
- 20–30%
- 55–65%
- 60–70%
Correct answer: 30–50%
The EPA recommends maintaining indoor relative humidity between 30% and 50% to discourage mold growth while maintaining occupant comfort.
Question 5: When inspecting a bathroom exhaust fan for mold-related concerns, what is the most critical functional check?
- Verify that the fan is vented to the exterior and not into an attic or wall cavity (Correct answer)
- Confirm the fan produces at least 200 CFM of airflow
- Check that the fan is on the same circuit as the HVAC system
- Ensure the fan has a built-in HEPA filter
Correct answer: Verify that the fan is vented to the exterior and not into an attic or wall cavity
Bathroom exhaust fans that terminate in attics or wall cavities dump moisture-laden air into enclosed spaces, frequently causing severe mold growth in those concealed areas.
Question 6: What is the purpose of an energy recovery ventilator (ERV) in preventing mold in a tightly sealed building?
- It brings in fresh outdoor air while transferring heat and moisture between airstreams to prevent humidity extremes (Correct answer)
- It recirculates indoor air through HEPA filters without introducing outdoor air
- It heats incoming outdoor air to 100°F to kill mold spores before distribution
- ERVs are designed to reduce radon levels, not humidity
Correct answer: It brings in fresh outdoor air while transferring heat and moisture between airstreams to prevent humidity extremes
An ERV exchanges stale indoor air for fresh outdoor air while transferring both sensible heat and moisture between the outgoing and incoming airstreams, maintaining ventilation without uncontrolled humidity swings.
CMI CMI HVAC Systems & Ventilation Inspection 2
What is 'thermal bypassing' in duct systems and how does it contribute to mold growth?