When I woke up this morning (a beautiful winter morning), I opened my curtains and noticed that the middle pane was covered in surface condensation, but the two adjacent panes were almost completely clear.

I know that there are various things I can do to reduce humidity in the room, and I will do that, but can anyone explain why the middle pane was so much worse than the others?

Could it be badly fitted? or is it just because it's bigger, further away from the edge of curtains, and therefore subject to less airflow. If it's badly sealed, could it be getting colder than the other two, and the first to get condensation.

Could it also be that water is somehow getting into the window frame?

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  • Are they double pane windows?
    – JACK
    Dec 24, 2020 at 17:30
  • yes - only recently fitted (a couple of years ago)
    – Rich S
    Dec 24, 2020 at 17:38
  • The right & left windows seem to have an inner frame that the center window does not have. That makes me think there is some real difference between them, which could affect the insulating properties/thermal transfer/condensation. Dec 24, 2020 at 17:57
  • @manassehkatz-Moving2Codidact What you’re seeing is the center window is fixed and the other two are operable. The operable panes need an extra frame in order to operate.
    – Lee Sam
    Dec 24, 2020 at 18:12
  • @LeeSam I suspected that might be the case. But in which case they may also be built a little differently, explaining the difference in condensation. Dec 24, 2020 at 18:23

2 Answers 2


Condensation is all about the dew point which is determined by the relative humidity along with temperature at the surface of the window. Although RH is probably consistent across all of the panes, temperature will vary due to air circulation or convection. This could cause one pane to gather condensation and the one next to it to be dry.
This isn't an issue if the condensation is on the exposed surface of the window. If they are double or triple paned and the moisture is between the panes it would indicate a leak in the seal which results in lowered efficiency.

  • it's definitely on the exposed surface.. I've had 'blown' seals before, and it's not that. It just seems so distinct between the panes, I would have expected a curve of some kind where the middle window has more, but the other two have a smaller amount lower down.
    – Rich S
    Dec 25, 2020 at 0:15

It looks like your window curtains open out toward the sides. The most probable reason the center pane saw more condensation is because it was where the center meeting point of the curtains occur when closed. That meeting point is going to allow more warm room air to enter at the center pane than over near the sides. When the natural convection in the room over the night the warm air entering at the center first meets the center pane and any moisture in the air will condense on the cold window. That air is now cooled to a point to when it passes behind the curtains across the outer panes toward the edges of the curtain it has much much less temperature difference compared to the window and thus far less chance of having additional moisture condense out.

If you left the curtains open all night you may find the condensation may be more uniform across all the panes. But on the other hand the difference of air flow at the window surface will be all different in this case, even depending on how the room air flow works, and you could actually see more condensation or none at all.

  • interesting observation.. the curtains are quite 'generous' so I will try to make the 'meeting point' of the curtains over to the right, to see if the RH window gets more condensation.
    – Rich S
    Dec 25, 2020 at 0:12

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