Condensation On Windows - Find Out Why You Get It. - 17/09/2018

There are some great things about Winter: wooly socks, flannel sheets, electric blankets and hot water-bottles. Soups, stews, apple crumble and snuggling up on the couch drinking hot chocolate. But there’s one thing about Winter that isn’t so great: Condensation on windows!

The monotonous chore of waking every morning to wipe moisture from windows or mop pools of water from sills is enough to make you forget all those wonderful cosy things that Winter brings.

So just what is window condensation? Why do you get it? And most importantly, how can you prevent it?


What causes condensation on windows?

Let’s get scientific for a moment and look at the fundamentals of condensation.

Condensation occurs when water vapour comes into contact with a cold, solid surface like an exterior wall or cold window. As the water vapour hits this cold surface it converts into a liquid form, which then trickles down the window and can pool on your window sill.

This water vapour can come from a range of sources. It could come from your breath — filling your bedroom all night long with no way to escape. It could be caused by boiling veggies on the stove or even from drying washing inside. All that moisture has to go somewhere, so it evaporates into the air, becoming a gas, then it makes its way to the window glass, then converts back into the liquid you see on your windows.

Window condensation is much more common in Winter because the difference in the exterior and interior temperatures is greater. Many of us like to stay warm in Winter and as a consequence may not open our windows as regularly as we might in the warmer months. This can mean our homes are less likely to be adequately ventilated and may struggle to deal with any excess moisture.

When you take a bottle of milk out of the fridge the water vapour in the air settles on the outside of the bottle, but only up to the milk line. If you leave the milk out for a while it will heat up. The liquid on the outside of the milk will evaporate again and as the milk temperature becomes closer to the temperature of the room, less water vapour will settle on it. The problem is, in Winter we never really want our indoor temperature to match the outdoor temperature. This means it could be more difficult to break the cycle of condensation forming on our windows.


How to stop condensation on windows

Manual Ventilation

According to Energywise, one simple way to reduce window condensation is to open multiple windows in your home for a short while, every day. This creates a through-draft which releases moist air and allows fresh air to circulate through the home. The downsides to manual ventilation are that firstly, it can be a hassle when you’re trying to stay warm inside. And secondly, if you’re not home during the daytime and need to leave windows open you might be concerned about security. Not only that, but coming home to a cold house isn’t the nicest way to start your relaxing evening!

If you are home during the day it can be easier to manually ventilate the home, however ventilation not only removes moisture from the air, it also lets out all the precious heat you are trying to keep in!

If you are able, focus on manually ventilating damp areas like the bathroom and kitchen. This can be made easier by installing extractor fans in these rooms that force out the moist, hot air as it is created.



Portable dehumidifiers are one way to reduce moisture and condensation during the Winter months. They are small units designed to pull moisture out of the air before it has a chance to condensate on windows and surfaces. The moisture is collected in a vessel within the unit, which needs to be manually emptied when full.

Dehumidifiers are available at most hardware stores and start from around $80 for the very cheapest small capacity models and increase in price from there depending on the brand and capacity of the model.

Unlike a full home ventilation system, dehumidifiers are only working to lower the moisture content in the room in which they are placed. They are not the most effective drying tool if you are after a whole home solution.

Compare Dehumidifier Prices



Capacity per Day


Arlec 2L Dehumidifier




Nouveau Dehumidifier




Dimplex 10L Collapsible Dehumidifier




Goldair Dehumidifier




Suki 16L Dehumidifier




Goldair Dehumidifier w/ Tank 12L White




Suki 16L Digital Dehumidifier




Suki 20L Dehumidifier with Heat




Delonghi Portable Dehumidifier 16L Blue




Prices taken from Bunnings and Mitre10 on 26/07/2018




Our Home Solutions Generator provides a personalised solution to help you choose the system that's right for you and your family.


Home Ventilation Systems

Having a home ventilation system (HVS) installed can be an effective way to get rid of window condensation and overall moisture from your home.

A home ventilation system works by pumping old stagnant air, moisture and airborne toxins out of the house, while also pumping fresh, much drier air into the home. This constant circulation and removal of damp air means that the air doesn’t contain enough water vapour to create condensation on your windows.

Having a Home Ventilation System in your home not only reduces moisture, it also reduces the likelihood of mould growth.  On top of this, having an HVS running makes your home easier to heat, as water vapour rich air is harder to heat than dry air.


Double Glazing

Some people believe that when they get double glazed windows and doors installed in their new home, they will no longer have to deal with the issues of window condensation. Unfortunately this is not always the case. 

Double glazed windows may help to reduce the occurrence of condensation due to the thermal break between the two panes of glass. When it comes to single glazed windows, the single pane is much the same temperature as it is outside. With double glazed windows, the pocket of air between the two panes is intended to help maintain the indoor temperature and in doing so, keep the internal pane closer to the internal temperature, which means that condensation is less likely to occur.

Double glazing is great for keeping warm air inside the home but it is not so great when it comes to letting moist air out of the home. This means that while the home may stay warm and toasty, that water vapour has even less chance of escaping through double glazed windows and once it reaches the windows it can cause condensation.

The good news is that once the issue of ventilation is addressed, your home may become easier to heat and the double glazed windows will be worth their initial expense.


Impacts of Condensation

Mould and Health Issues

Unlike us, mould thrives in humid, damp environments. Condensation heavy homes are great incubators for mould. Mould loves damp places that stay damp for long periods of time.

Mould spores are more likely to be present in damp air and persons who are allergic or sensitive to mould can become unwell. Asthmatics and people with respiratory issues can also be negatively affected by mould spores, as can those with weakened immune systems, such as infants or the elderly.

In order to help prevent mould issues in your home it is important you regularly ventilate your home.


Harder to Heat

According to joint guidelines issued by EECA, Ministry of Health and the HPA, dry homes are easier and more economical to heat than moist, damp homes. This may mean that regardless of how much you crank that heater, your condensation and dampness issues may not go away until you address the ventilation issues causing the condensation.

It is common to avoid opening windows in Winter — after all we’re all trying to keep our homes warm, not let the warm air out. So instead of airing our homes out, many people just add more heat. Frustratingly though, without ventilation, the warmer we make the temperature indoors, the more condensation that may form on our windows.


Don’t Jeopardise your Investment

When we fail to address the issues of condensation in our home, we may be putting our largest investment at risk. A house isn’t just a home - according to Statistics NZ, for most Kiwis it is likely to be their largest financial asset, so it pays to take good care of it.

If you are concerned about the condensation in your home why not book a free home assessment today? An experienced HRV team member will take your needs and the needs of your home into account, giving you a total home solution that will keep your home dry and warm and more comfortable for years to come.