Ventilation & IAQ
Because the air you don’t see can hurt you the
most.
Opening Hook — A Silent Problem in Every Building
Have you ever walked into a room and felt tired,
dizzy, irritated, or uncomfortable—even though the temperature felt
“normal”?
No alarms.
No visible smoke.
No obvious warning.
Yet something was wrong.
That “something” is often poor ventilation
and bad indoor air quality (IAQ).
Ventilation problems don’t shout.
They whisper—until health complaints, mold, odors, corrosion, and safety risks
start piling up.
This chapter dives into the real-world ventilation & IAQ issues
HVAC professionals face every day—and how to diagnose and solve them with
confidence.
61. Poor Indoor Air Quality Complaints
What occupants usually say
- “The air feels stuffy.”
- “I get headaches by afternoon.”
- “There’s a strange smell.”
- “People keep falling sick.”
These are classic IAQ red flags.
Common causes
- Inadequate fresh air
- Dirty filters or ducts
- Poor air distribution
- High CO₂ levels
- Mold or microbial growth
Step-by-Step Troubleshooting
- Talk to occupants — symptoms matter
- Check outdoor air intake operation
- Measure CO₂ levels
- Inspect filters and coils
- Verify ventilation rates
Expert Insight
Comfort complaints are often air-quality complaints
in disguise.
62. Exhaust Fans Not Working
Why exhaust fans matter
Exhaust fans remove:
- Odors
- Moisture
- Pollutants
- Combustion by-products
When they fail, contaminants build up fast.
Common reasons for failure
- Motor burnout
- Belt damage
- Blocked ducts
- Electrical issues
- Backdraft dampers stuck closed
Quick Checks
- Is the fan running?
- Is airflow actually exiting?
- Are dampers opening?
- Is the duct blocked?
Pro Tip
A spinning fan does not guarantee ventilation—airflow
matters.
63. Humidity Too High in Summer
Why high humidity is dangerous
- Mold growth
- Musty odors
- Discomfort
- Reduced cooling efficiency
Typical causes
- Oversized AC units
- Insufficient runtime
- Poor ventilation balance
- High outdoor air moisture
- Faulty controls
Corrective Actions
- Verify latent load calculations
- Improve airflow across coils
- Add dehumidification control
- Check outdoor air quantity
Rule of Thumb
Comfort cooling without humidity control is
incomplete cooling.
64. Dry Air Problems in Winter
Common complaints
- Dry throat and skin
- Static electricity
- Nose irritation
- Cracked furniture or flooring
Why it happens
Cold outdoor air holds very little moisture.
Heating it without humidification makes indoor air extremely dry.
Solutions
- Install or service humidifiers
- Seal excessive air leaks
- Control ventilation rates
- Monitor indoor RH (30–50%)
Common Mistake
❌ Turning off humidifiers to
“save energy”
✅
Proper humidity saves health and materials
65. Mold Growth in Ducts
Why mold grows
Mold needs:
- Moisture
- Darkness
- Organic material
HVAC ducts provide all three when poorly maintained.
Warning signs
- Musty odors
- Visible black/green spots
- Increased allergies
- Persistent IAQ complaints
Immediate Actions
- Identify moisture source
- Repair leaks or condensation
- Clean and disinfect ducts
- Improve filtration
- Control humidity
Expert Insight
Mold is not a cleaning problem—it’s a moisture
problem.
66. ERV / HRV Ventilation Troubleshooting
What ERVs & HRVs do
- Bring in fresh air
- Exhaust stale air
- Recover heat (and sometimes moisture)
Common issues
- Reduced airflow
- Clogged cores
- Fan imbalance
- Control failure
- Poor commissioning
Troubleshooting Checklist
- Inspect filters and cores
- Verify supply/exhaust balance
- Check frost protection
- Confirm control sequences
Pro Tip
Balanced ventilation is more important than maximum
ventilation.
67. Carbon Monoxide (CO) Leak Detection
Why CO is deadly
- Colorless
- Odorless
- Invisible
- Life-threatening
Common sources
- Boilers
- Furnaces
- Generators
- Gas water heaters
- Poorly vented equipment
Detection & Prevention
- Install CO detectors
- Inspect flue connections
- Verify exhaust draft
- Ensure fresh air supply
- Test combustion regularly
Non-Negotiable Rule
CO safety is not optional. Ever.
68. UV Light Systems Troubleshooting
Purpose of UV systems
- Kill bacteria and viruses
- Prevent mold on coils
- Improve IAQ
Common problems
- Burnt-out lamps
- Dirty quartz sleeves
- Poor placement
- Incorrect operating hours
Maintenance Steps
- Verify lamp operation
- Clean sleeves regularly
- Replace lamps annually
- Confirm safety interlocks
Expert Insight
UV works best as prevention—not a cure.
69. Exhaust Air Backdrafting Issues
What is backdrafting?
Instead of air exiting, exhaust air re-enters
the building.
Causes
- Negative building pressure
- Blocked exhaust paths
- Poorly designed intakes
- Wind effects
Risks
- CO re-entry
- Odors
- Moisture problems
- Health hazards
Fixes
- Balance supply and exhaust
- Relocate air intakes
- Add draft inducers
- Improve pressure control
70. Mechanical Room Ventilation Compliance
Why mechanical rooms need ventilation
- Heat removal
- Combustion air
- Safety
- Code compliance
Common violations
- Insufficient air openings
- Blocked louvers
- Poor exhaust
- No makeup air
Best Practices
- Follow local codes
- Verify airflow calculations
- Keep louvers unobstructed
- Inspect regularly
Pro Tip
Mechanical rooms are lungs for equipment—don’t
suffocate them.
Common Mistakes & Smart Fixes
❌ Ignoring occupant complaints
✅
Treat complaints as diagnostic tools
❌ Assuming ventilation is “set
and forget”
✅
Ventilation needs regular verification
❌ Over-ventilating without
control
✅
Balance IAQ with energy efficiency
❌ Skipping sensors and monitoring
✅
Measure what you manage
Powerful Summary — Air Is the First Comfort System
Ventilation and IAQ are not accessories to HVAC.
They are HVAC.
In this chapter, you learned how to:
- Identify IAQ complaints
- Fix exhaust failures
- Control humidity year-round
- Prevent mold growth
- Troubleshoot ERVs/HRVs
- Detect CO safely
- Maintain UV systems
- Stop backdrafting
- Ensure mechanical room compliance
Final Reflection
People forgive uncomfortable temperatures.
They do not forgive unsafe air.
Call to Action
Start listening to the air.
Measure it.
Balance it.
Protect it.
Because good HVAC doesn’t just condition
air—it protects lives.
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