Ventilation systems

Ventilation systems

Stop mould and “crying windows”.

Our database comprises ventilation systems from most major brands available in New Zealand. We use specifications supplied by the manufacturer. We also have reliability and satisfaction data from our 2017 reliability survey for some of New Zealand’s most popular brands of ventilation systems.

Before diving into our database, check out our guide on choosing a ventilation system to narrow down your options and select the right type for you.

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Choosing a ventilation system

If you’re sick of stale air and weeping windows, but don’t know where to start, we’re here to help. Follow these steps, in conjunction with using our database, to narrow your options and find the best ventilation system for your home.

1. Sort out heating and insulation

You should only opt for a ventilation system if you’ve installed floor and ceiling insulation (if possible) as well as a decent heat source. In living areas this should be a fixed, efficient source of warmth, such as a heat pump or wood burner. In smaller rooms, portable plug-in electric heaters are sufficient.

2. Tackle moisture at the source

Identify any sources of airborne moisture, such as bathrooms, then consider installing a shower dome or extractor fan. Also look at fitting a plastic moisture control sheet to stop rising damp, and check if water is pooling under the home from any blocked drains.

3. Time for a dedicated ventilation system?

If problems persist, you can opt for a mechanical ventilation system, but note these cost upwards of $2000 (installed). A dehumidifier is a cheaper stopgap solution, but will cost more to run than a ventilation system.

4. Positive or balanced pressure?

The first thing to consider when looking at ventilation systems is whether you should go for positive pressure or balanced pressure – don’t confuse either with heat transfer systems.

  • Positive pressure (also known as forced air) ventilation systems work by blowing drier air into your house from the roof space above the ceiling or, in some types, from outside. They suit older houses with wooden joinery better than modern houses with sealed aluminium joinery (unless windows are opened or additional vents fitted). But blowing cold air in from the roof space in winter will require you to ramp up your heating.
  • Balanced pressure (also known as heat exchanger) ventilation systems extract warm, damp air from living spaces and pass it through a heat-exchanger to heat up dry air, which the system brings in from outside. This can fully meet Building Code requirements. They work best in modern homes and don’t have the same unintended cooling effect as positive pressure systems, so choose a balanced pressure system if your home is well-sealed.
  • Heat transfer systems aren’t ventilation systems, they simply haul warm air from one room to another (usually from a living area to bedrooms, etc.), but you can add a heat transfer system on to some ducted ventilation systems.

5. Reliability

Our 2017 reliability survey of 804 Consumer members with ventilation systems found DVS and HRV systems are very reliable. Nearly 90% of respondents who owned these brands said their system had never needed repair. The reliability of MoistureMASTER and SmartVent systems was below average at about 70%. These were the only 4 brands with sufficient respondents for us to comment on their reliability and satisfaction.

6. Filters

Ventilation systems filter the air coming from your roof space or the outdoors. There are a wide array of filter types, usually designated by a letter and a number (for example, G4). In general, “F” filters remove smaller particles than “G” filters, so will catch more dust and airborne bacteria. The higher the second number, the more effective the filter – for example, an F7 filter will catch more nasties than an F6 filter. Some manufacturers offer optional advanced filters: carbon filters can be good for removing odours from the air (for example, the smell of everyone blasting their wood burner on a cold winter day), while HEPA filters are claimed to be effective at removing allergens. We recommend going for the standard filter initially, and only adding a carbon or HEPA filter if you find you’re dealing with odours indoors or suffering from allergies.

7. Optional heaters / summer cooling

Some systems offer the ability to add heaters to ducting, which can be useful for positive pressure systems if you’re concerned about cool air from the roof space reducing indoor temperatures. Summer cooling options, where the ventilation system introduces cooler air to the home, are available but can be expensive.

Controlling condensation

Winter condensation is a widespread problem. In winter we spend more time indoors, creating moisture from cooking, cleaning, washing and even breathing. When we're out of the house we leave it closed up for security.

Insulation adds to the problem. We trap the heat of living areas by keeping doors shut and using heavy curtains and carpets.

This all comes at a price. Warm air holds water better than cold air. Because it's sealed in, the moisture builds up then condenses on cold surfaces such as windows and walls.

The solution is simple – better ventilation. Making it happen is less simple.

If you're living in a draughty old Victorian villa, you shouldn't have too much of a problem with ventilation. But modern houses are much more airtight, so natural ventilation is minimal.

Extra heating is part of the solution, combined with water extraction near the sources. Rangehoods intercept steam from the kitchen; extractor fans are effective at drying out bathrooms. You could also consider a dehumidifier. While these can help control condensation, they’re expensive to run (up to $2.50 a day), often noisy, and must be run constantly. With a dehumidifier you are controlling the symptoms and not dealing with the problem. While not the ideal solution, dehumidifiers have their place.

An automatic ventilation system is a better way of controlling condensation. Whichever way you attack the problem, remember it's even more effective if the amount of water released into the air is reduced.

Sources of moisture

Activity Litres
Cooking 3.0 / day
Clothes washing 0.5 / day
Showers and baths 1.5 / day (per person)
Dishes 1.0 / day
Clothes drying (unvented) 5.0 / load
Gas heater (unflued) Up to 1.0 / hour
Breathing, active 0.2 / hour (per person)
Breathing, asleep 0.02 / hour (per person)
Perspiration 0.03 / hour (per person)
Pot plants As much as you give them

Check your ceiling insulation

If you don't have any insulation, get this installed first. If existing insulation has become dislodged, compacted or wet through roof leaks, it won't be fully effective. It may even be inadequate for your climate.

Fix all insulation problems before considering how to improve your heating and ventilation.

Stop it at the source

Simple ways to reduce the amount of water released into your home.

  • Fit extractor fans over the cooktop or stove, and in the bathroom. They must be ducted to the outside.
  • Always use close-fitting lids on pots when cooking.
  • Vent the clothes dryer to the outside.
  • Close doors when cooking, showering or using the dryer, to limit the spread of moist air.
  • Avoid using unflued gas heating.
  • Limit the number of pot plants in the house.
  • Check that the ground under the house is dry. If it's wet, cover with polythene (if this is feasible), taping the joints, and ensuring a tight fit around piles. Check that drainage systems are diverting water away.
  • Fix any leaks in the roof or around windows.
  • Remove open vented downlights or replace them with new downlights that don’t leak your warm damp air into the ceiling.

Building code requirements

The building code has minimum requirements for ventilation: all the air in your house should be changed every 3 hours. It says the air in kitchens should be changed every hour; in bathrooms every 2 hours.

To achieve this, the code suggests extractor fans in kitchens and bathroom – and open windows elsewhere – to bring in fresh outside air.

But you won’t want to leave windows open while you are away from home or overnight, for security reasons. An option is to have trickle vents inserted into your windows. These can have insect screens and shutters to control pests and the amount of air flow. Examples are at www.joinerydev.co.nz and www.woodman.co.nz.

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