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What's the best type of home ventilation system for NZ houses?

7 June 2019
What's the best type of home ventilation system for NZ houses? What's the best type of home ventilation system for NZ houses? Blog

If winter’s chill is leaving your home’s windows wet with condensation, you might be thinking seriously about whole house ventilation – a proven way to reduce moisture inside your home.

Once you start digging into the subject, it’s easy to get confused because house ventilation systems fall into two categories: heat recovery ventilation systems (often called HRV systems) and positive pressure ventilation (PPV) systems. They are very different and only one type is really relevant for New Zealand’s climate – PPV.

The difference between HRV and PPV systems

HRV systems have a heat exchanger that extracts heat from air that’s leaving the ventilation system and mixing it with the fresh air entering the system.

Heat recovery ventilation systems aren’t suitable for most parts of New Zealand. They are designed for very cold, dry climates like Canada. Possibly the only area of New Zealand that might qualify for a true HRV system is somewhere like Central Otago, and then only in an airtight home in the middle of winter.

Positive pressure ventilation systems, like Unovent, are totally different. They bring fresh, filtered air from the roof space into rooms below. This action pushes stale, moist air out through gaps under doors or around windows, and through bathroom and kitchen vent systems.  So your home becomes drier and the air is continually being changed, which is better for family health.

Benefits of an intelligent PPV system

Sometimes the air in a roof space is not suitable for circulating around your home. It’s either too hot, too cold or too moist. So it’s important to choose a PPV system that automatically makes intelligent decisions. Unovent uses the Unobrain® controller, which decides if the air in the roof space is suitable for circulation. If it isn’t, the ventilation system will go on hold until conditions change.  Unovent can also be augmented with PollenGuard®, to filter pollen from the fresh air entering your home.

How moisture gets inside homes

The air in your roof space or attic is nearly always less humid that the air inside your home. There are various reasons for this:

  • Humans create moisture just by breathing and perspiring. Our bodies are about 60% water[1]; even our bones contain water. As soon as you have a house full of humans, you have moist air.
  • Kitchens and bathrooms release water into the internal atmosphere of your home. Every time you have a shower or boil a kettle, you’re adding to the moisture burden.
  • Sometimes we do things like drying washing inside our homes. While it may seem like a good idea to have a drying rack of damp clothes inside when it’s raining outside, it’s healthier to use a dryer that vents to the outdoors.
  • Another factor that can increase moisture levels inside your home is the use of un-flued gas heaters, which put water into the air as they burn gas.
  • If you’re fond of house plants, you can expect higher humidity levels. Plants release water into the air through their respiration system. 

Why moisture is a problem in homes

Damp homes promote mould, mildew and dust mites, which can cause respiratory problems and exacerbate allergic conditions like asthma. Damp homes also deteriorate faster than dry homes, because moisture affects building materials and paint. What’s more, a damp home is harder to heat; even if you have insulation and a heat pump, your energy bill will most likely be higher. 

To assess the humidity levels in your house, try using a hydrometer. You can buy these gadgets on TradeMe and sites like Ali Express.  Take readings over a few days or weeks in different rooms of your house, to see what sort of moisture levels you have inside. The ideal humidity level for health and comfort is about 40 to 50%. In the cooler months, it may have to be lower than 40% relative humidity to remove condensation on windows. More about ventilation for a healthier home.

“Dust mites require a relative humidity in excess of 45–50%. Therefore, to prevent the multiplication of dust mites in houses, the relative humidity during the heating season should be below this value.” Moisture and Ventilation Guidelines, World Health Organisation[2]

Talk to an expert before you choose a ventilation system

It costs nothing to find out whether a PPV system is right for you and your home. If you have a roof cavity or attic, your home could be ideal (and your winter could be healthier!). For a no-obligation assessment and quotation over the phone, call 0800 UNOVENT (0800 866 836) or email sales@unovent.co.nz and we'll be in touch.