Condensation On Windows? - Learn How To Prevent It - 12/05/2017

You will likely experience some form of condensation in your house. If condensation is left uncontrolled, your house can become cold, damp and unpleasant to live in.  

What Is Condensation?

Most commonly, condensation appears as water droplets covering the inside of your windows. Condensation will form on any surface, but is most noticeable on cold surfaces.

Condensation occurs because the air inside your home contains moisture. Warm air holds more moisture than cool air, so when the air cools down, water vapour condenses and will become noticeable on windows and walls.

The ratio of water vapour in the air to the maximum amount of water vapour the air can hold at a particular temperature is expressed as relative humidity (RH). For example, a RH of 30% means that the air contains 30% of the moisture it can possibly hold at that particular temperature...When air can hold no more moisture at a given temperature (i.e. the RH is 100%), the air is said to be saturated”

This moisture will also be absorbed by carpets and furnishings, making them feel damp and can cause mould and odour. Microorganisms that thrive in these conditions can cause allergies and asthmatic conditions.

 Boiling Kettle Producing Steam

Relative Humidity Explained

Image the air is a 'bucket' holding a proportion of water. As the air ois cooled, the 'bucket' gets smaller and therefore the proportion of water inside the 'bucket' increases. If air continues to cool the 'bucket' will diminish to a size where it is now full with water. i.e. it is 100% full.

Table Explaining The Relative Humidity At Different Temperatures

If the air is cooled any further the 'bucket' will become even smaller and the water will overflow. In reality this occurs where the air temperature has cooled so much that it can no longer hold the water as vapour.

Looking at data between 1981 & 2010 the annual relative humidity averages in the main centres of New Zealand are as follows:

Auckland - 82%

Hamilton - 84%

Tauranga - 79%

Wellington - 83%

Christchurch - 85%

Dunedin - 76%

For a more comprehensive look into your regional climate check out NIWA's NZ Climate Overview


What Is The Dew Point?

Simply put the Dew point is the point at which the air can no longer hold all the water in the atmosphere (sometimes also referred to as the saturation point) and you will start to see visible signs of moisture in your home. This is most often noticed by the presence of 'crying windows' or foggy mirrors but this moisture will also be present throughout your home with other materials like carpet absorbing it which reduces the more obvious visible signs. 


What Causes Condensation?  

You may first notice condensation on the windows but the windows are not the cause of condensation. Activity in the home creates airborne moisture. When the moisture is not removed, it can condensate on surfaces. 

The moisture is produced by everyday activities such as cooking, washing, bathing and exercising. Your breathing also creates moisture in the air.

The average New Zealand family produces around eight litres of moisture in the home each day.


Common Sources of Moisture In The Home 

Breathing - 4 people in a house will produce 11L in a 14 hour period

Sleeping - 4 people produce 1.12L per day

Showering/Bathing - 1.5L per shower/bath

Cooking - 3L per day

Dishwashing - 1L per wash

Washing Clothes - 0.5L per wash

Drying Clothes - 5L per wash

Gas Heating - 1L per hour


Areas In New Zealand Subject To Condensation

Levels of mould and condensation in New Zealand are widespread. Both issues are triggers of respiratory diseases, asthma and hospital visits.

In technical terms:

“New Zealand has a year round, outdoor RH of between 70–80% in coastal areas and about 10% lower inland. Indoor relative humidities are generally lower than outdoor relative humidities ranging, in New Zealand dwellings, from 30% to 65% during the day-time in a “dry” house, and 50% to 75% in a “damp” house. Cold bedrooms can have relative humidities of 80% - 90% at night-time. Generally, most people will be comfortable in a humidity range of 30–80% if the air temperature is in a range of 18–24ºC”


How To Prevent Condensation

The good news is that the 2016 State Of The Home Survey found that Kiwis are becoming more aware of both the causes and solutions:

“HRV CEO Bruce Gordon says the survey showed increasing awareness about the combination of insulation, heating, and ventilation is seen as being the key to creating a warm, dry home.

"It used to be insulation and some sort of heating source that people were focused on, but now insulation, heating, and ventilation go hand in hand, and increasingly double glazing is becoming a high priority for people”.

Try these home ventilation tips:

  • Avoid drying clothes indoors.
  • Use lids on pots when cooking
  • Do not dry clothes over radiators
  • Ensure tumble driers are properly vented to the exterior of the house
  • Ensure extractor fans are well maintained and remove moisture not only from the room, but from the entire building envelope i.e. ventilated externally
  • When cooking, drying laundry, or showering, make sure you let the water vapour escape outside or remove it with externally vented mechanical extractors i.e. rangehood.


Ventilation Systems

Home Ventilation systems work by replacing the moisture-laden air in your home with drier air. This both reduces condensation and improves air quality as a result. Through a process called positive pressure, the stale indoor air is flushed out and replaced with drier, filtered air.

HRV Ventilation systems can reduce dampness by ensuring that the air in your home is cycled two to four times per hour. HRV’s Next Generation Ventilation system acts as the lungs of your home by replacing the stale indoor air with fresh filtered air.

The best ventilation systems take drier and often warmer air from the roof space and filter it, purifying the air, before distributing it evenly throughout your home.

Drier air makes heating and cooling your home more energy efficient. This airflow can also reduce the causes of mould, damp, excess condensation and odours. With HRV Ventilation, this airflow process is controlled using an intelligent touch-screen keypad.


Moisture can get in to your home from under the floor, especially if water pools form under your house or the soil is damp.

Covering the ground under the house with a vapour barrier, like a sheet of heavy polythene, can help keep moisture out. Installing under-floor insulation can also help. Keep plumbing in good repair and ensure water is not leaking under your house.

The area under your house should be well drained.


What Do Dehumidifiers Do?

One way to help eliminate some built-up moisture is to use a dehumidifier. A dehumidifier draws in the moisture laden air from around the room, extracts the water and stores it in an inbuilt container. You then dispose of the water by removing and emptying the container. Dehumidifiers, can be noisy and need to be matched carefully to the room size in order to work well. It’s important to note that dehumidifiers do not address moisture at the source like an extraction fan or rangehood.

Hopefully, you can easily make a few changes to reduce the level of condensation in your home. If you need a complete home solution, talk to HRV today.


Get In Touch With HRV

Considering an HRV Ventilation System as the perfect solution to keep your home comfortable year round?

Request a Free Home Assessment from a trained HRV technician today.

Not sure what the best option for your home is?

Try our online Home Solutions Generator now, it only takes 3 minutes and once completed we’ll give you some immediate advice on the right products for your home along with approximate costs.

Further Reading:



Condensation. (n.d.). Retrieved April 19, 2017, from

Contact Us. (n.d.). Retrieved April 19, 2017, from

Hawkes, C. (n.d.). New state-of-home survey shows renters left in the cold. Retrieved April 19, 2017, from

Home Ventilation Systems. (n.d.). Retrieved April 19, 2017, from

Humidity and condensation in a building - How to control it. (n.d.). Retrieved April 19, 2017, from


News. (n.d.). Retrieved April 19, 2017, from

Products for a healthier home. (n.d.). Retrieved April 19, 2017, from