Ventilation Introduction

NZ Building Code G4 Ventilation (summarised):
“...Buildings shall have a means of collecting or otherwise removing: cooking fumes and odours; steam from laundering, utensil washing, bathing and showering; odours from sanitary and waste storage spaces; poisonous or flammable fumes and gases...”

• Natural Ventilation for the above is acceptable as long as opening windows in each room have an area of 5% or more of the floor area of the room.

• For internal rooms without natural ventilation, mechanical ventilation (extraction fans) must be installed to extract the air at given rates. Residential requirements are listed on the right.

• Where fans are used to remove moisture and other contaminants from kitchens, bathrooms and laundries in housing, the exhaust air must be ducted to the outside at the flow rates mentioned above.

• The above requirement for ducting also applies to any fan in those areas, even if there is an opening window (i.e. even if the fan is not a requirement to comply with ventilation regulations, but is installed as an optional extra).

Bathrooms
The regulations require a fan capable of a minimum extraction capacity of 25 litres per second when installed

Toilets
The regulations require a fan capable of a minimum extraction capacity of 25 litres per second when installed

Kitchens
The regulations require a fan capable of a minimum extraction capacity of 25 litres per second when installed

Laundries
The regulations require a fan capable of a minimum extraction capacity of 25 litres per second when installed

• The above mentioned flow rates are minimum allowable flow-rates. In general these would not be enough to overcome excessive moisture and condensation problems encountered in modern homes.

• The ventilation industry has a “Recommended Air-Changes per Hour” approach solution. i.e. An air flow rate sufficient to remove / replace the total volume of air in a given room a specified number of times each hour.
  
  Obviously fans will not necessarily be left running for an hour - a fact which is taken into consideration in the formula.

For example: A bathroom is recommended at between 11 & 15 air-changes per hour. Therefore 15 changes per hour means the total air in the room would be replaced after 4 minutes.
E.g. (60 minutes @ 15 changes per hour = 4 minutes)

This would mean an average bathroom usage of 12 - 16 minutes resulting in the total air volume being changed 3 to 4 times. This equates to a rate of 15 ACH.