What is condensation?
The air around you holds a certain amount of moisture (humidity).
The hotter the air is, the more moisture it can contain.
The cooler the air is, the less moisture it can contain.
When warm, moist air hits a cold surface, the air temperature decreases.
This colder air can no longer contain as much moisture.
As a result, the excess moisture condenses into liquid form on the cold surface.
That’s condensation.
Why do I have condensation?
Throughout the year, your home will contain the same amount of air moisture (on average).
In summertime, we tend to open the windows a lot more.
This means that stale and moist air is naturally ventilated and removed from your home.
In wintertime, we tend to shut our windows to keep heat in.
This results in low air movement, and stale moist air being trapped inside.
In conjunction, the windows of your home will be much colder, especially in the mornings.
This combination makes winter the peak season for condensation problems in homes.
Does double glazing help?
Double glazing is great for maintaining temperature(hot or cold) within the home.
Double glazed windows do not get as cold on the interior surface, meaning condensation is much less likely to form.
However, having double glazing does not mean your home has a healthy air environment.
While effective in limiting symptoms, double glazing doesn’t address the moisture buildup in your house.
How to reduce condensation
Prevention and Extraction
The most effective approach is to reduce the sources of indoor moisture. Common culprits include:
- Drying laundry indoors
- Cooking or boiling water without using rangehood extraction
- Showering without an extractor fan or leaving the bathroom door open
- Non-ducted or non-condenser dryers releasing moist air into the house
- Faulty or absent extractor fans
- Open water sources like fish tanks or laundry tubs
- Pools or spas connected to the home interior
- Dampness from underfloor areas (may require a ground moisture barrier)
- Roof or plumbing leaks (having full gutters leads to backflow into the soffit areas)
- Overflowing gutters that cause water ingress into soffits
If your home lacks proper extractor fans or has poor air circulation, our residential electrical services can help. We also recommend electrical maintenance and servicing to upgrade ventilation wiring and extraction systems reducing condensation risks and improving your indoor air quality.
How do you fix poor ventilation in a house?
Start with the cheapest step, opening windows, then sort out the wet areas. That is the order The Conduction Company works in.
Open the windows. Natural ventilation costs next to nothing. The only reason not to is the cold in winter, and even then, if you are out for several hours a day, opening the windows even just a crack while you are away makes a drastic difference. Close them when you get home and turn the heating on, so the heat stays in.
Duct every wet area to the outside. Bathrooms, laundries, and kitchens make a lot of steam, and decent extractor fans stop it getting into the rest of the house. The Conduction Company has seen extractor fans in the right locations make a drastic difference to a whole home's humidity, especially where there is a dryer in the laundry, without a full positive pressure ventilation system, although that is the best solution.
Check the dryer. A dryer not ducted to the outside, with no extractor fan in the same room, is a huge issue The Conduction Company finds in homes. "Essentially all of the moisture that is on your clothing as soon as they come out of a washing machine, all of that moisture gets pushed back into your home if your dryer isn't adequately ducted to the exterior," says Jordan Statham, its director. That is the same moisture that ends up as condensation on your windows in the morning, and on the ceiling, where mould grows.
To warm a bathroom as well as vent it, The Conduction Company compares heat lamps, wall heaters and towel rails in its guide to bathroom heaters in NZ.
How do you fix poor ventilation in a bedroom?
Keep the door open for a start, and if the room still runs wet, fit positive pressure ventilation. That is The Conduction Company's answer, and the reason is breathing. "The human body produces a significant amount of moisture just by breathing," says Jordan Statham, director of The Conduction Company, and with two people in the room the effect is doubled. Overnight, that moisture builds up in the bedroom air. An open door gives some passive ventilation from one room to the next. But if the room has moisture problems and heavy condensation in the mornings, the best fix is a positive pressure ventilation system. It forces fresh air into the room and pushes the stale, moist air out, so it does not build up into damp air and wet windows by morning.
Using Dehumidifiers and Air Conditioning Units
Dehumidifiers and AC units on ‘dry mode’ both reduce humidity by drawing warm, moist air across cold internal coils.
This causes condensation to form inside the unit, where it’s collected in a water container (dehumidifiers) or drained outside (air conditioners).
These two systems are effective at reducing air moisture levels within the home.
However, these systems are energy-hungry and limited to specific rooms.
Air conditioning units set to 'Dry' mode will produce cold air, which may be undesirable in winter.
IMPORTANT NOTE:
Many people mistakenly believe that air conditioners serve the same function as ventilation systems. When in reality these systems perform two very different functions. In normal operation
- Air conditioners have a minor effect on humidity, and a major effect on temperature.
- Ventilation systems have a major effect on humidity, and a minor effect on temperature.
Ventilation Systems
Ventilation systems such as HRV, DVS, and SmartVent provide whole-home ventilation solutions.
The Conduction Company compares the three brands, and which suits an older or airtight home, in its guide to HRV vs DVS vs SmartVent home ventilation systems.
These systems draw warm, dry air from your ceiling cavity, filter it, then push it throughout your home.
These are known as positive pressure ventilation systems.
They raise the indoor pressure slightly, which in turn pushes stale, moist air out through:
- Extraction ducting (e.g., kitchen and bathroom fans)
- Gaps in joinery, under doors, or through the garage
Compared to dehumidifiers or air conditioning, positive pressure ventilation systems are much more energy efficient.
They also work continuously to maintain healthier, drier air across the entire home
How to lower humidity in a house
Stop the moisture at the source first, then ventilate: that is how The Conduction Company lowers humidity in a house. Breathing, cooking, showering and drying clothes all add moisture to the air. Duct every bathroom, laundry and kitchen to the outside with a decent extractor fan or rangehood, and make sure the dryer vents outside. A ventilation system then keeps driving the humidity down across the whole home, swapping stale, damp air for drier air all day.
Dehumidifiers work too, but Jordan Statham, director of The Conduction Company, calls them "a very energy intensive way" to pull moisture from the air, and they only work in the room they sit in.
Do heat pumps help with condensation and damp in NZ homes?
Only a little, says The Conduction Company: a heat pump is not the fix for condensation and damp in NZ homes. A heat pump or air conditioner mainly changes the temperature, has a minor effect on humidity, and adds no fresh air. Only a ventilation system deals with damp, mould and condensation properly. Where a home is both cold and damp, The Conduction Company recommends both.
Does DVS stop condensation?
A DVS system greatly reduces condensation, The Conduction Company finds, but no system stops all of it. A positive pressure system like DVS replaces damp indoor air with drier air from the roof space, so far less moisture reaches the cold glass. The Conduction Company checks the moisture sources first, because an unflued gas heater, a dryer venting inside, or a wet subfloor will beat any system you install.
Why do I still have condensation with HRV?
Because no ventilation system can remove every drop of window condensation, The Conduction Company explains, and something may be beating it. On the coldest winter days, with humidity at its peak and people in the home making moisture, the physics will not allow it. A system can drastically reduce condensation, so read the fine print on any "no crying windows" guarantee. If it is still heavy, look for a moisture source such as a dryer venting inside, and check the filter: a blocked or long overdue filter is the most common reason a system that used to work well stops feeling like it does anything.
How to stop condensation on windows and walls in NZ houses
Cut the moisture at its source, then ventilate: that is The Conduction Company's way to stop condensation. Duct the dryer to the outside, run an extractor fan in every bathroom and laundry, and use the rangehood when you cook. If you are out for several hours a day, leave the windows open even a crack while you are away.
Windows run wettest on winter mornings, when warm, moist air meets cold glass. Double glazing keeps the inside of the glass warmer, so less forms, but it does not remove the moisture from the house. A ventilation system has the largest effect by far, because it keeps replacing damp indoor air with drier air. Where a home is both cold and damp, The Conduction Company recommends ventilation and a heat pump together.
For a bathroom wall that keeps running wet, The Conduction Company's tip is to keep the extractor fan running, shut the bathroom door, and put an oil heater just inside it. The room warms up, and the fan draws the moist air out slowly. A dehumidifier also works in the room it sits in, but Jordan Statham, The Conduction Company's director, calls it "a very energy intensive way" to pull moisture from the air.
How do I stop condensation inside my house?
Lowering the moisture in the air is the only way to stop condensation inside your house, says The Conduction Company. Condensation forms when warm air carrying a lot of moisture meets a cold window and can no longer hold it all. If the air meeting the glass is warm and dry, it has nothing to drop.
There are two ways to bring the moisture down. The first is extraction: fans in the kitchen, bathroom and laundry pull the steam out before it mixes with the air in the rest of the house. The second is positive pressure ventilation, from systems such as SmartVent, DVS and HRV, which forces fresh air in and pushes the stale, moist air out. Opening doors and windows helps as well. Any moist air you get out of the house is moisture that cannot end up on the windows.
How to stop condensation on windows overnight in NZ
Three things working together cut overnight window condensation, says The Conduction Company: extraction, ventilation, and making less moisture. Extraction means fans in the bathroom, kitchen and laundry, running whenever those rooms are making moisture. Ventilation means a positive pressure system bringing fresh air in and pushing the stale, moist air out. Making less moisture is covered in the tips below.
Many people expect double glazing to fix it, and it does help. The inside of the glass stays warmer, so the moist air is not cooled as much and less condensation forms on it. But the moist air is still in the house. "You haven't solved the problem, you've just addressed the symptom," says Jordan Statham, director of The Conduction Company. Double glazing is excellent at keeping heat in, which is its main job. Lowering the moisture in the air is what deals with the cause.
How to stop condensation in your home: expert tips for DIY
Start by making less moisture, says The Conduction Company: moisture never put into the air cannot reach the windows. Put a cover on a fish tank. Dry clothes outside rather than inside, so the water in them does not end up in the house. If you use a dryer indoors, make sure it is ducted to the outside, or run the laundry's extractor fan while it is on. Open the doors and windows when you can.
Where a dryer has no duct or the laundry has no fan, The Conduction Company covers the options in its guide to venting a dryer and choosing extraction fans.
How to stop condensation in your home: expert tips for the bathroom
In a bathroom, pull the air out rather than push it in, says The Conduction Company. A bathroom, like a kitchen or a laundry, should run at negative pressure, with a suitable extractor fan pulling the moist air out. A positive pressure ventilation outlet in a bathroom could do the opposite, and force the moist air into the rest of the home.
If the bathroom still stays wet overnight with the fan running while you use it, The Conduction Company's answer is a continuous extraction kit. It runs on a low speed 24 hours a day, so the bathroom is always at negative pressure. When it senses steam from a shower, it boosts to full speed and pulls the steam out, then drops back to low. "We'd definitely recommend continuous extraction in bathrooms," says Jordan Statham. The Conduction Company explains when continuous extraction suits a house better than positive pressure in its guide to changing a ventilation system.
A dehumidifier works too, but Jordan does not rate it as the best answer. It only dries the room it sits in, and it uses much more power than a fan pulling the air out.
Will DVS kill existing mould?
No, a DVS system will not kill existing mould, and nor will any other ventilation system, says The Conduction Company. What ventilation does is slow mould down. Mould, in Jordan Statham's words, "loves a warm and moist environment", and a ventilation system takes the moisture away, so mould is less likely to spread.
Mould that is already there has to be treated to get rid of it completely. That means proper cleaning and, depending on how bad it is, a professional treatment, and sometimes repainting the affected areas.
Summary
Condensation is a natural occurrence, but too much of it can signal issues with moisture levels in your home. The Conduction Company lists the other signs to look for, from a musty smell to mould in wardrobes, in its guide to signs of poor ventilation in a home.
While double glazing and heating helps reduce symptoms, it won’t solve the core problem.
The most effective long-term solutions are:
- Reducing moisture sources and effectively using extractors
- Installing a Ventilation system (to force fresh air in, and push moist/stale air out) - this will have the largest effect on condensation by far.
- Using dehumidifiers and AC units on 'Dry' Mode in homes where ventilation systems are not feasible, or not yet installed.
Frequently asked questions
In NZ, if ceiling cavities are showing condensation, why would this be?
Usually because the ceiling void is closed off and cannot breathe, The Conduction Company finds. Warm, moist air gets trapped in the void, and overnight it meets the cooling roof and condenses, dripping onto timber, insulation and plasterboard. It shows most under steel or iron roofs and in well sealed cavities. The Conduction Company's fix is an in-line fan that pulls the moist air out of the void, with a passive inlet at the other end so drier air replaces it.
Is it better to have vents high or low to stop condensation in a house?
High, for a positive pressure ventilation system: The Conduction Company fits the outlets in the ceiling. Each one sits centred in the room but out towards the corner furthest from the door, so the air sweeps the whole room and leaves through the doorway without dead spots.
Need Expert Advice?
Want to know what the right setup is for your home?
Speak with your local professionals or reach out to a licensed electrician for a practical assessment and advice on managing indoor moisture safely.
Contact us to discuss extraction fan upgrades or ventilation system installation to help reduce condensation issues
