Balanced pressure ventilation systems
Balanced pressure heat recovery ventilation systems are particularly suitable for modern homes in colder areas of the country, if they’re already well heated and reasonably airtight.
How they work
These systems have two fans for two separate air streams:
- one fan supplies fresh outdoor air into the house through ceiling vents
- the exhaust fan extracts an equal volume of air from inside the house and discharges it outside
- some of the heat from the exhaust air is moved to the incoming air in a heat exchange unit, usually located in the roof cavity.
Some products include extra features to make use of heat in the roof cavity on sunny winter days, or to avoid the incoming supply air being warmed up by the exhaust air during summer nights.
In winter, the heat exchanger moves a portion of the heat in the warm exhaust air to the cold supply air, thus reducing the heat loss associated with ventilation. The overall effectiveness of the heat exchanger depends on two factors:
- having an airtight house - to make sure that almost all ventilation air passes through the heat exchanger
- the temperature difference between the inside and outside air.
The larger the temperature difference, the more heat the heat exchanger will recover. If you live in a warmer part of New Zealand or if large parts of your house are cold a lot of the time, then a heat exchanger is less likely to pay for itself in energy savings.
To ventilate effectively, the air must be able to flow freely between the supply and exhaust vents inside the house, so your internal doors need gaps around them or vents. Be careful not to create a ‘short circuit' route between the supply and exhaust vents, which may result in areas of the house being bypassed.