Dew diligence on condensation: tips to reassure concerned customers

Dew diligence on condensation: tips to reassure concerned customers

Featured Article
11 Apr 2019

As Featured in Pro Installer Magazine - 01/19

Phil Brown, European regulatory marketing manager at Pilkington United Kingdom Limited, part of the NSG Group, explains the different causes behind condensation appearing on windows.

For the glass and glazing industry, the transition to spring often sees an influx in customers asking why they are seeing external condensation on their windows, especially from those with higher performing, low-emissivity glazing. 

While some homeowners and building managers may see it as a nuisance, they should know that external condensation is a tell-tale sign that energy-efficient windows are doing their job! 

However, if condensation is appearing on the inside surface or between the panes of double or triple glazing, there may be more cause for concern. So, when should installers advise worried customers depending on where the water is appearing?

1) External condensation: Know the dew point

External condensation happens because of what’s called the ‘dew point’ – the temperature at which air can’t hold any more water vapour, causing droplets of liquid water to form. When the air next to a piece of glass reaches this temperature – which varies with humidity – condensation forms on the surface. 

This phenomenon is more likely to happen in the spring and autumn, when cold morning and evenings combine with high levels of humidity in the air.

External condensation is more common with modern, high performing, low-emissivity (low-e) glazed windows, as the outer pane is colder as a result of heat being retained inside the home. With single or older double-glazed windows, more heat is passing through, warming the outer pane and reducing the likelihood of external condensation. An analogy is frost on roofs - those with good loft insulation can remain frosted for a long time, while those without quickly defrost.

There is little that can be done to avoid condensation to the outside of the window entirely without specialist glazing. However, its occurrence doesn’t tend to last for long. Once the window pane warms from the sun, the moisture evaporates. The air movement from a gentle breeze can also help to clear it.

But, not all panes are affected by early morning condensation, even in the same window. Small differences in the orientation and the position of objects outside, such as trees or a close building, can change the surface temperature of the glass to the point that one pane suffers and another doesn’t. 

Pilkington Anti-condensation Glass offers a solution that prevents the onset of external condensation and improves the view through windows by allowing the external surface to get a little warmer, reducing the likelihood of the air reaching the dew point. As the coating is pyrolytic, it is durable enough to be used on surface one (i.e. facing the outside), as well as being robust and easy to clean. It can be combined with low-emissivity glass as the inner pane, so no compromise is needed on thermal performance.

2) Condensation in between panes

Condensation within the cavity of insulating glass unit (IGU) is likely to indicate a failure of the edge seal. There could be several reasons for early failure of any IGU, including inappropriate installation method, incompatible materials, unsuitable frame design, missing setting blocks, blocked drainage and ventilation slots and poor-quality units.

It is essential that components used in the IGU and frame are compatible to maximise lifetime.  Most warranties will stipulate that IGUs should be handed, stored, installed and maintained in accordance with relevant standards and industry guidelines, such as GGF datasheet 4.2.  

All IGUs should be manufactured in accordance with BS EN 1279 and CE Marked specifically in accordance with BS EN 1279-5 and, for greater confidence, be subjected to a recognised third-party product certification scheme. 

3) Condensation on the inside: turn the kettle off!

As well as occurring externally, condensation can also happen on a cold internal facing surface in a room with high moisture content. Common examples include in bathrooms, as a result of hot water use, in gyms, where perspiration raises the humidity, and cafés where food and drink preparation along with many people’s breathing can put a lot of moisture into the air.

There’s little installers can do to stop the occurrence of internal condensation in bathrooms, as the humidity can be so high. However, specifying low-emissivity double or triple glazing should help in other situations, as the inside pane is less likely to get cold enough to make the water vapour in a room condense on the glass surface.

If customers find condensation to be a nuisance, it could be worth recommending improving the ventilation by installing a greater number of, or more powerful, extractor fans at the sources of water vapour. Increasing the room temperature so that the air can hold more water vapour without condensing can also help. 

As uptake in high-performance, thermally insulating glazing increases, queries about external condensation are also likely to increase. However, it’s important to inform customers that this proves that the glass is performing as designed, and that solutions are available with specialist glazing if required.