Safety boundary: Never block, resize or reroute combustion-air openings or appliance vents without approved design.
Exhaust must leave safely
Fuel-burning appliances depend on intact venting or chimneys. Corrosion, disconnection, nests, ice or incorrect materials can create hazards.
Homes can depressurize
Large exhaust fans, fireplaces and tight construction can reduce indoor pressure and interfere with natural-draft appliances.
Condensing equipment
Modern furnaces and water heaters may use plastic venting and produce condensate. Materials, slope, supports and terminations must follow the appliance listing and local rules.
Warning signs
Soot, moisture stains, melted venting, unusual odours, corrosion, backdrafting or repeated safety shutdowns require prompt evaluation.
Useful questions to record
- Can everyone leave safely now?
- Which emergency service or utility should be called from outside?
- What information can be recorded without re-entering?
Related guides
Carbon Monoxide and Home HeatingHow carbon monoxide can enter a home and what alarms and appliance maintenance can—and cannot—do.Gas Odour or Suspected Fuel LeakA simple emergency response that avoids switches, sparks and delay.HVAC, Filtration and Indoor Air QualityWhat central HVAC can contribute—and what requires source control or ventilation.Smoke and Carbon-Monoxide Alarm ChecklistA practical record for alarm locations, testing and replacement dates.