Home ventilation systems

Home ventilation systems use fans to move air into the house and can provide continuous ventilation regardless of the weather and without the need to open doors and windows, provided the model you choose is well designed and installed.

Is a home ventilation system right for you?

A well designed and installed home ventilation system can offer you the convenience of good ventilation by delivering required air replacement continuously and independently of weather conditions.

Ventilation systems are not the only way to ventilate. Opening your doors and windows regularly is a simple and effective way to ventilate most homes - read more about ventilating your home.

Note that a home ventilation system is not a good solution for fixing cold and dampness problems in homes.

If you are trying to make your existing home warmer and drier, your money will be better spent on sorting out your insulation, installing an effective heating system and tackling dampness problems at source.

If dampness is your main concern, then address the source of the moisture problem first, before looking at ventilation systems.

Be aware that the performance of ventilation systems can vary widely depending on a range of factors - the type of system and how well it is installed, your type of house and the climate.

Ask your supplier for independent test performance reports for the system they are proposing. You should also get a ‘no questions asked' guarantee of performance that includes removal of the system if it doesn't work and repair of all damage to your home - e.g. holes in ceilings should be fixed to prevent undue air leakage.

Can a home ventilation system heat your house?

Ventilation systems aren't effective heating solutions. If you're after a heating solution, there are several good options including efficient heat pumps, modern wood burners and wood pellet burners, and efficient gas heaters. Learn more about these heating systems.

Pumping air from the roof space air is insufficient to heat a home

University of Otago research shows that the heat available from moving roof space air into your home (as the most common type of ventilation system does) doesn't provide significant heating benefits compared with what you need to properly heat a home in winter.

The research recommends that people don't install this type of system for heating purposes. Read the Otago University research report.

The research also found that pumping air from the roof space into the living area would often push internal temperatures away from the desired level, rather than toward it.

In summer, roof cavities quickly become excessively hot, and systems that pump roof space air into your house without a summer bypass will have to be turned off for extended periods in order to avoid overheating your house.

Optional electrical heating unit add-ons - there are more efficient and effective ways to heat a home.

Some ventilation system suppliers offer the option of an electrical heating unit add-on, to provide some pre-heating of air coming from the roof cavity when it is cold. These are known as electric in-line duct heaters.

Most electric in-line duct heaters don't have sufficient capacity to meet a home's heating needs.

Like any other type of electrical heaters (except heat pumps), electrical in-line duct heaters are a relatively expensive and inefficient way to heat a home, particularly if you already have a more effective heater (like heat pump, wood or wood pellet burner, or flued gas heater).

Electric in-line duct heaters lose some heat through the ducts, so it's actually more efficient to use a heater directly in the room you want to heat.

Contaminants from the roof space

Another thing to consider is that roof spaces often contain vermin, mould, and dust. As suppliers have yet to prove that home ventilation system filters are effective at reducing these contaminants to safe levels, EECA recommends that the supply air of home ventilation systems be sourced from the outside, not from the roof cavity.

The New Zealand Building Code requires homes to have means of ventilation with outdoor air to maintain air purity. Ventilation systems that draw air from the roof space and not directly from outside do not comply with ventilation standard NZS4303:1990 "Ventilation for acceptable indoor air quality" and cannot be used to comply with the Building Code Acceptable Solution for ventilation.

Types of home ventilation systems

There are two types of home ventilation systems commonly available in New Zealand:

  • Positive pressure roof cavity ventilation systems
  • Balanced pressure heat recovery ventilation systems

Positive pressure/roof cavity heat transfer ventilation systems

Positive pressure/roof cavity ventilation systems are the most common type available in New Zealand. They force filtered air from the roof cavity into the house through a single, or multiple, ceiling vents. This pushes air inside the house out through gaps around doors and windows and other leakage areas.

How well these systems are able to ventilate the whole house depends on the performance of the fans, distribution of the ceiling vents throughout the house and the building air tightness.

In draughty houses the ventilation system will be unable to force the air into each room of the house. If the roof cavity is not properly sealed from the inside of the house (for example if you have recessed downlights) the system will short-circuit, i.e. indoor air will migrate into the roof cavity and be pumped back into the house again.

Air quality

Roof cavities are often polluted with dust, mould and vermin. To reduce the amount of contaminants in the air supply, positive pressure/roof cavity ventilation systems are usually fitted with filters. The quality of the air entering the house is highly dependent on the filter type and cleanliness. As suppliers have yet to prove that home ventilation system filters are effective at reducing these contaminants to safe levels, EECA recommends that the supply air of home ventilation systems be sourced from the outside, not from the roof cavity.

Balanced pressure heat recovery ventilation systems

Balanced pressure heat recovery ventilation systems are particularly suitable for homes in colder areas of the country, if they are already well heated and if they are reasonably airtight.

These systems have two fans for two separate air streams. One fan supplies fresh outdoor air into the house through several ceiling vents, while the exhaust fan extracts an equal volume of air from inside the house and discharges it to the outside. The exhaust air stream transfers some of its heat energy into the incoming air in a heat exchange unit, usually located in the roof cavity.

Some products include additional features to utilise heat in the roof cavity when it is available on sunny winter days, or to avoid the incoming supply air being warmed up by the exhaust air during summer nights to assist with cooling.

To ventilate effectively, the air must be able to flow freely between the supply and exhaust vents inside the house, requiring gaps around or vents in internal doors. Care is also required to ensure that a ‘short circuit' route is not created between the supply and exhaust vents which would result in areas of the house being bypassed by the system.

In winter, the heat exchanger transfers a portion of the heat in the warm exhaust air to the cold supply air, thus reducing the heat loss associated with the ventilation. The overall effectiveness of the heat exchanger depends on having an airtight house, to ensure that uncontrolled ventilation losses are minimised so that almost all ventilation air passes through the heat exchanger.

More information

From the Resource Centre

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