Why Ventilation Matters
Australians spend 90% of their time indoors, yet indoor air can be 2-5x more polluted than outdoor air. Indoor sources include: cooking fumes, cleaning products, building materials off-gassing (VOCs), moisture from breathing and activities, carbon dioxide build-up, and combustion products from gas appliances.
Natural vs Mechanical Ventilation
- 1 Natural ventilation (openable windows, vents): free, no running costs, effective in mild climates — ineffective when external air is hot, humid, or polluted
- 2 Spot mechanical ventilation (exhaust fans in bathrooms/kitchens): removes moisture at source — minimum requirement for wet areas under NCC
- 3 Whole-house mechanical ventilation (HRV): continuously exchanges indoor air with filtered outdoor air — best for airtight, well-insulated homes in cooler climates
Bathroom and Kitchen Exhaust Fans
Exhaust fans in bathrooms and kitchens are mandatory under the NCC for new buildings. Key specifications: bathroom fan minimum 25L/s (litres per second) extraction rate; kitchen rangehood minimum 150L/s. Run bathroom fan for 15-20 minutes after showering to fully remove moisture. Fans must vent externally — never into a ceiling cavity.
⚠️ Watch out: Exhaust fans venting into the ceiling cavity (instead of externally) are a building defect and cause severe mould in the ceiling space. Check your fans actually vent through the roof or wall.
Subfloor Ventilation
Homes with suspended timber floors (common in elevated Queensland homes, older southern states homes) need adequate sub-floor ventilation to prevent condensation causing timber rot and mould. Minimum: 1500cm² of ventilation per 10m² of floor area per AS 1684. If sub-floor areas show condensation, mould on joists, or musty smell — add mechanical sub-floor ventilation fans.
Heat Recovery Ventilation (HRV)
An HRV system continuously exchanges stale indoor air with filtered fresh air, recovering 70-85% of the heat energy in the outgoing air. Ideal for airtight, well-insulated homes in cooler climates (VIC, TAS, ACT, alpine areas) where opening windows for ventilation is uncomfortable in winter. Cost: $3,000–$8,000 installed. Very effective for health and comfort in high-performance homes.
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