Common Ventilation Issues Reference

Why this matters

Ventilation affects indoor air quality, energy use, moisture control, + building health. Many customer issues - humidity, smells, mold, comfort - trace back to ventilation. The tech who understands ventilation diagnoses correctly + helps customers fix root causes. This is the field card.

Ventilation basics

Purpose:

• Remove stale air (CO2, odors, pollutants)
• Bring in fresh outdoor air
• Control humidity
• Provide combustion air to appliances

Types:

Natural ventilation:

• Air leaks through building envelope
• Windows opened
• Old leaky homes have plenty
• Newer tight homes need mechanical

Mechanical ventilation:

• Fans + ducts
• Continuous OR intermittent
• Bath fan, kitchen hood, whole-house

Balanced ventilation:

• HRV (Heat Recovery Ventilator) OR ERV (Energy Recovery Ventilator)
• Exhaust + intake balanced
• Heat exchange between airstreams
• Most efficient

Bathroom ventilation

Purpose:

• Remove moisture (shower)
• Remove odors
• Prevent mold

Fan requirements:

• 50 CFM minimum residential
• Continuous (run after shower) OR timer
• Vent to outside (not attic, not crawlspace)
• Properly sized for bathroom

Common issues:

• Fan venting to attic (creates moisture problem)
• Fan undersized
• Fan too loud (customer doesn't use)
• Vent damper missing OR stuck
• Vent terminating with no flow

Kitchen ventilation

Range hood:

• Remove cooking moisture + smoke + odors
• 100+ CFM typical
• Vented to outside (best) OR recirculating (less effective)
• Filter cleaning regularly

Common issues:

• Recirculating when ducted possible
• Filter clogged
• Vent damper missing
• Termination poor
• Make-up air insufficient (tight homes need)

Whole-house ventilation

Continuous mechanical exhaust:

• Bath fan on timer / variable
• Pulls fresh air through leaks / windows
• Simple but limited

Continuous balanced (HRV/ERV):

• Fresh air in; stale air out
• Heat exchange
• ASHRAE 62.2 standard
• Newer + tight homes

Periodic operation:

• Manual venting (window opening)
• Limited reliability

Attic ventilation

Purpose:

• Remove summer heat (cools roof + attic)
• Remove moisture in winter
• Prevent ice dams (winter)

Types:

• Soffit vents (intake at eaves)
• Ridge vent (exhaust at peak)
• Roof vents (exhaust)
• Gable vents (older)
• Powered fans

Code requirements:

• 1 sq ft net free area per 150 sq ft attic floor (some calculations 1:300 with balance)
• Balanced intake + exhaust

Common issues:

• Insufficient intake (no soffit vents OR blocked)
• Insufficient exhaust
• Imbalanced (more exhaust than intake)
• Insulation blocking soffit vents
• Powered fan creating negative pressure (pulls conditioned air from house)

Crawlspace ventilation

Traditional: vented to outside

• Outdoor air enters
• Moisture problems in humid climates

Modern: encapsulated (sealed)

• Vapor barrier
• Conditioned air OR dehumidifier
• Better for energy + moisture

Issues with vented crawlspace:

• Humid outdoor air enters
• Cool crawlspace = condensation
• Mold growth
• Wood rot

Why ventilation matters

Health:

• CO2 builds up (cognitive issues)
• VOCs accumulate (off-gassing furnishings)
• Allergens concentrated
• Mold growth

Building:

• Moisture in wrong places = mold + rot
• Frozen pipes (poor ventilation contributing)
• Equipment fails

Comfort:

• Stale air feels off
• Humidity issues
• Temperature variations

Diagnosing ventilation problems

When customer reports:

"House feels stuffy":

• Inadequate fresh air
• Check ventilation system operation
• Bath fans run after showers?
• Whole-house ventilation working?

"Bathroom mold":

• Bath fan inadequate
• Or not used
• Or venting to attic

"Attic feels wet in winter":

• Inadequate attic ventilation
• Warm moist air from house entering attic
• Air sealing needed first; then ventilation

"Kitchen smells linger":

• Range hood inadequate OR not used
• Filter clogged
• Recirculating ineffective

"Crawlspace damp":

• Vented crawlspace in humid climate
• Encapsulation recommendation
• Address drainage too

Sizing exhaust fans

Bath fan:

• 1 CFM per sq ft of bath floor minimum
• 50 CFM minimum
• 100 CFM for large bathrooms

Range hood:

• 100 CFM minimum (recirculating)
• 250-400 CFM (ducted)
• Larger ranges = larger hood

Whole-house ventilation:

• Per ASHRAE 62.2 calculation
• Based on home volume + occupants
• Typically 50-150 CFM continuous

Vent termination requirements

Bathroom + kitchen:

• Outside (not attic, not crawlspace)
• Through roof OR through wall
• Distance from windows / intake
• Backdraft damper

Dryer vent:

• Outside
• Smooth bore duct preferred
• Max length per code
• Backdraft damper

Code violation: dryer vented to attic / crawlspace (lint = fire risk + moisture)

Combustion air

For gas appliances:

• Outside air OR conditioned space air (if adequate)
• Per NFPA 54 calculation
• Newer construction often dedicated combustion air

Insufficient combustion air:

• Yellow flame
• CO production
• Equipment failure
• Backdrafting

Common ventilation mistakes

• Bath fan venting to attic (most common code violation)
• Dryer venting to attic / crawlspace
• Range hood recirculating when ducted possible
• Attic ventilation imbalanced
• Powered attic fan pulling conditioned air
• Crawlspace vents open year-round (humid climate)
• Whole-house ventilation absent in tight homes
• Bath fan never run

Cross-trade observations

HVAC: ventilation issues affecting comfort + humidity, ductwork includes whole-house ventilation Roofer: attic ventilation visible from roof; ridge vents, roof vents, condition Plumber: bath fan vent termination; sewer vent stack adequacy Pest control: moisture from poor ventilation attracts pests; crawlspace condition Cleaner: smells from inadequate ventilation; mold in poorly ventilated spaces

Indoor air quality testing

For comprehensive assessment:

• CO2 monitor (indication of ventilation adequacy)
• VOC meter
• Humidity / temp
• Particulate counter

Some service techs offer; others refer to IAQ specialists.

Specific scenarios

New tight construction:

• Mechanical ventilation required by code in many jurisdictions
• HRV / ERV common
• Customer needs education on operation

Old leaky home:

• "Plenty of natural ventilation"
• Customer may have other issues (no specific complaint)
• Energy efficiency tradeoff

Bathroom mold problem:

• Bath fan upgrade
• Operation discipline (run during + after shower)
• Door undercut for makeup air
• Maybe whole-house humidity issue

Crawlspace musty:

• Vapor barrier
• Encapsulation
• Drainage
• Dehumidifier
• Vent strategy

Mid-rise / multi-family ventilation:

• More complex
• Common ventilation
• Building-wide systems
• Different code (commercial)

References

• ASHRAE 62.2 (Ventilation + Indoor Air Quality)
• IMC + IRC ventilation requirements
• NFPA 54 (combustion air)
• HVI (Home Ventilating Institute) fan ratings
• Manuall internal: Indoor Air Quality Testing, Attic Moisture + Ventilation Diagnosis