Mist or condensation on glass?
We see water vapour either on the glass or inside the double or triple glazed glass units. This is a common issue in the morning during the winter in the UK. Condensation (water droplets) on the glass window can be wiped off with a towel; if not, then the double or triple glazed glass unit has failed and so the view through the glass looks misty as if clouds inside the glass unit. See an example below between glass with mist and newly replaced glass without mist.
How does mist form…humidity?
Condensation occurs on windows, because glass and window frames are usually the coolest surface in the room, so water vapour in the air condenses on them first. There are many sources of moisture in the home; for example showering, cooking, dishwasher, washing machine and even breathing out. Drying clothes or towels on a radiator also produces a lot of condensation (i.e. water from those wet clothes evaporates into the room air during the drying process.)
Does condensation mean the window is faulty?
It depends. If condensation can be wiped off with a towel (i.e. it’s not inside the window glass panes,) then the window glass is not faulty, meaning humidity is too high. You need to take action to reduce humidity. If condensation is inside the glass panes, then the glass unit is faulty and that glass unit needs replacement. So water droplets running down on the glass surface, doesn’t mean the window is faulty.
How to measure or check humidity?
We can measure humidity in the air with a hygrometer. Ideal humidity level is between 40% – 60%. If humidity is too low, then we feel uncomfortable as the room air becomes too dry. Common symptoms are dry throat, sore eyes, stuffy nose, itchy or dry skin. Also young children may experience nose bleeding, as dry air can damage or crack the delicate nasal membrane lining inside their nose. Higher humidity above 60% or more causes condensation on glass or windows and mould in our room walls.
How to reduce humidity and prevent mould?
Room air can be treated like a sponge; hotter air has a higher capacity to hold water before water vapour starts to sit on another surface. Increasing heating during the winter will increase the capacity of air to hold more water, alternatively we will need fresh air supply in the room to prevent condensation. However, fresh air supply can’t be maintained easily during the winter as UK weather is very cold. So a balance needs to be struck between fresh air supply and more healing (i.e. more heating equals higher bills.) It’s a good idea to leave the window slightly ajar but secure, when outside and increase heating while we are in the room.
Is misted glass a serious problem?
Condensation can ruin the appearance of windows and the rest of the house, it will reduce the amount of light that enters the home and obscure our view through the window. Excessive condensation can damage wooden frames and cause mould on room walls. Windows can remain misted, if water gathers between the panes of glass; this can slowly rot window frames, dampen walls and allow mould to grow.
Can new double glazed glass be misted?
Double or triple glazed window glass usually lasts 10 years or more, before showing signs of mist inside the glass units. The two panes of glass are joined with a sealant. These sealants lose integrity after many years, which creates weak points around the edge of the glass unit and allows moisture to enter between the two panes of glass. This occurs naturally and cannot be prevented as high summer temperatures cause the air between the panes to expand and contract during the winter, causing sealant to become weaker over time.
How can misted windows be fixed?
Misted glass needs to be replaced. You would need to contact a professional to replace misted window glass. New glass will usually last over 10 years, before showing any sign of mist. Keeping humidity in check will reduce the chance of glass becoming misty. Also keeping window sill, frame and seals clean helps glass units to last longer.