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  Good Repair Guide: Improving Internal Ventilation

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All houses need a constant supply of fresh outdoor air to replenish indoor oxygen levels and replace stale, moisture-laden air that is generated by household activities.

Good indoor air quality can be recognised by an internal environment that is not stuffy or musty, does not have stale cooking odours and has low (below 75%) relative humidity. Good indoor air quality is essential for the health and comfort of the occupants.

Poor indoor air quality comes from a range of sources, including:
- high indoor moisture levels from unvented kitchen or bathroom steam, unvented gas heaters or clothes dryers
- pollutants and discharges from solid-fuel burners, open fires, gas heaters and cookers, and occupant activity such as smoking inside
- volatile organic compounds (VOCs) given off by new building materials, paint and carpets
- outdoor sources of pollution (that is, vehicle emissions, or fireplace emissions such as coal fires).

High moisture levels create conditions in which moulds, bacteria and dust mites thrive, and this can put pressure on the respiratory and cardiovascular systems of some occupants, causing a range of adverse health effects such as headaches; sinus congestion; coughing and sneezing; eye, nose, throat or skin irritations; dizziness and nausea and a general lack of feeling well.

In most New Zealand homes, opening windows will be sufficient to meet most air quality requirements, so long as this is used in conjunction with localised externally vented air extraction systems such as kitchen rangehoods and bathroom extractor fans to remove moisture and pollutants. Where the occupants are not able or choose not to open windows regularly, there is likely to be a need for other means of ventilation.

This Good Repair Guide outlines strategies for maintenance tradespeople to improve the ventilation of spaces within a domestic building.