Appliances
Ventilation systems
Introduction
Does your house suffer from "crying windows"? A ventilation system could help.
If your home suffers from streaming windows, mouldy curtains and a damp unhealthy feeling, you need to improve your ventilation. We explain how to stop the sources of moisture, and what to look for in a ventilation system.
Note: this report does not contain test results or brand-specific recommendations, but we do compare the price and features of 70 ventilation systems.
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. But who wants to throw open the windows and replace all that lovely warm (wet!) air, heated at some expense, with a wintry blast from outside?
The solution
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 |
Stopping the sources
If you have not already attended to these:
- 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.
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.
Building code requirements
The building code has minimum requirements for ventilation: all the air in your house should be changed every three hours. It says the air in kitchens should be changed every hour; in bathrooms every two 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.com and www.woodman.co.nz.
Types of system
An automatic ventilation system is a much more effective way of reducing condensation than using a dehumidifier. And it's much more convenient than having to open and shut windows.
There are 2 main types of ventilation systems:
- Positive pressure or 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.
Read more about positive pressure systems.
- Balanced pressure / 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 more airtight, modern homes.
Read more about balanced pressure systems.
Which system is best?
This depends on the design of your house, its floor area, the location, how much sun the house gets, the type of roof ... even the local climate.
Before you install any system, do some homework. We've outlined how the different designs work and some of their pros and cons which should help you decide whether your house is suitable for any of the systems available. Consider what you want to achieve against the types of system – and also look for any extra features you might need to meet your particular requirements.
For best results, a system should be designed specifically for your house and your needs. But this can be quite costly, especially if you choose a fully automated system with multiple outlets or other options.
We recommend getting quotes from several installers who are familiar with your local climate.