One of the most common complaints I have received in my career of exporting windows was usually not long after installation. An angry call from a disappointed customer that he has faulty glazed units. “They’ve misted up!!!! The seals have failed or there is no Argon inside!!!” Those in the industry will know.
So what’s going on? More than likely one of 3 things. And it all depends on where the condensation is. Remembering that condensation occurs when warm air (being able to hold more moisture) comes into contact with a cold surface being forced to dump moisture (in the form of condensation). Like on your toilet cistern when you’re in the shower.
Situation 1 – The condensation is on the inside of the window
This is unlikely to be the case if you have new windows as triple glazing and warm spacers minimize thermal bridging meaning there are less cold surfaces on which condensation is likely to form. If this is happening we should observe the following:
- Lack of appropriate ventilation – It is necessary for all dwelling spaces to have the appropriate ventilation. Most countries have building regulations that stipulate the required liter per hour air changes depending on room type. Kitchens and bathrooms have the highest requirements due to the moisture produced. Ventilation is commonly designed into the building through either passive stack ventilation or more often nowadays balanced mechanical ventilation using a heat recuperation system. As a last resort air vents can be incorporated into walls or windows.
- Triple glazing – some markets still adopt double glazed units.
- Use of warm glass spacers – eg, Swiss spacer, chromatech etc… Most internal condensation occurs around the perimeter of the glass where the glass spacer is.
- Be sure to order windows with 90% Argon gas. In Poland this is standard but in some countries they are still using air.
- Be sure that windows have low-e coatings. Note triple glazed units have 2 low-e coatings (2nd and 5th surfaces) where double glazed units have generally one low-e coating. Commonly on the 3rd
- Adopt good installation practices. An installation solution that minimizes thermal bridging and air leakage. Air leakage around a window frame can eventually lead to mold growth as condensation is always present at the non-air tight junctions.
Situation 2 – The condensation is in-between the glass sheets.
If this is the case then you do in fact have catastrophic failure of the glazed unit. But you would be surprised how many clients are convinced this is the case and are wrong.
But there is a tell tale sign. Low-e coatings comprise a metallic coating that when subject to the moisture in air are susceptible to decomposition. When this occurs you will see a rainbow effect within the glazed unit something similar to the effect of oil on a puddle.
Situation 3 – The moisture is on the outside of the window.
This is what’s happening in the picture above and these windows have over 15 years, double glazing and steel glass spacers. So why is this happening? Usually in the morning. The outside surface of the glass has cooled through the night. The air has increased temperature in the morning. As the external glass surface is colder than the air it now creates a cold surface where condensation can form. The fact the moisture remains on the outside of the glass confirms the insulated glazed unit is doing it’s job. The heat from the inside of your house is not transferring to the outside pane of glass and evaporating the condensation. Note the perimeter has no condensation which demonstrates my old steel spacers are causing some thermal bridging. Hmmm – maybe time to get some new windows?