When we wake up in the morning, we're observing a significant amount of condensation on the bedroom windows around the edges on the inside (inside the house not between the panes). We had new windows installed in the spring, and we didn't have this issue last winter.

Is it likely that there's a draft around the windows keeping the windows cold? If so, how do I detect and/or fix that?


  • We have an electric radiator that we keep near the windows that we run typically for 2 hours starting when we go to bed
  • We have thick curtains that we draw closed when we sleep
  • We sleep with the door closed to block sound
  • Thanks everyone for the great answers so far. I've started experimenting with your solutions and I'll let you know what I find. Commented Jan 28, 2011 at 14:30
  • Are the new windows single or double pane? Gas filled? Low-E?
    – Bryce
    Commented Dec 4, 2013 at 9:24

11 Answers 11


I would guess that the problem is not a draft from the windows, but moisture in the room, probably caused by having two people sleeping in a closed room.

The warm, moist air in the room will hit the cold window and water will condense. To eliminate the problem, get more air circulation - open the door, or open the window a tiny bit. At least try it for a couple of nights to see if that solve the problem.

  • thanks, I'll try the cracking the door over next couple of nights. Too cold to crack the window. Commented Jan 26, 2011 at 21:01
  • 3
    This works partially when it's not too cold out. Even with the door cracked, the heat up and the ensuite exhaust fan on I was still getting some condensation on days when it was -29 Celcius (approx. -20 degrees Fahrenheit) outside. I may have to accept some condensation on super cold nights. Commented Feb 16, 2011 at 15:31

Chris is on the right track. A single a pane window is R1, the most expensive double pane window money can buy is R2.4. Not much difference, huh? Glass gets cold, excessive moisture in the room is condensing on the glass, that simple. Either stop breathing or get some air moving through the room or lower the humidity in the house or that room with a dehumidifier.

  1. Get a small Hygrometer, anything will do, less than $10 works well
  2. If you have up to %50-%55, you should not get condensation on double pane windows.

I had single pane that was totally wet every morning; I could fill a glass with the amount of condensation on that window. Replaced it with double pane and now there might only be a bit condensation on the lowest half inch of the window (lower -> colder).

Condensation happens as a factor of:

  1. Indoor air relative humidity
  2. the difference in temperature between the inside and outside air.

If you keep your house warmer, and that in turns heats the inside surface of the window, you will get less condensation. That is why people explained that if you do not cover your window with curtains you are less likely to get condensation. That is because the inner surface of the window now gets heated by the inside air. When you cover the window, you are increasing the insulation for the house (good thing) but that is because you are no longer hearting the inner window surface. So, the inner window gets colder. When it gets colder, the air in the room comes in contact with it and cools down.

When Air cools down, this is where it is important to understand relative humidly. The humidity you measure is relative. Relative to the air volume. I hope everyone remembers that the volume of the air changes as a function of its temperature. So, if you measure 60% humidity at 70 Degrees, you will see that when the air cools down to lets say 50 degrees the humidity will rise (don't know the formula, but lets say it can rise to 75%).

So why do you get condensation?

  1. because the surface of the window is cold (either draft, it being single pane or badly insulated double pane, or it is simply cold in your house)
  2. And because when the air in the room reaches that , its relative humidity approaches 100% and you get water.

Things you can do

  1. lower humidity (measure it first) by ventilating the house when outside humidity is lower
  2. keep humidity low by using external air fans when showering and cooking
  3. improve the windows insulation (but you said it is new, so I guess you tried that. unless you bought a single pane window...)
  4. Improve window insulation by using Bubble Wrap (I tried it, it works!)

If you find that your in-house humidity is high (70-80%) all the time and you cannot get it down.. we have the same problem (-: I wish I knew what to do about that.


Try leaving the curtains open during the night just as an experiment. I bet they will not build any condensation. This happens to use with our roman shades. The curtains act as an additional layer of insulation, and it gets really cold between the window and curtain. Somehow this barrier causes the condensation our house.

  • You are unlickly to get match condensation if you don't have a humidity problem on double glazed windows.
    – Walker
    Commented Jan 27, 2011 at 16:01

We had new windows installed in the spring

Your old windows would have let in lots of drafts, you now don't have enough ventilation. If the new windows have trickle vents use them in all the rooms, otherwise get legal advice over the fact that substandard replacement windows have been fitted.

Also don’t dry washing inside unless the dryer is vented to the outside and check that your extractor fan in the bathroom removes all he steam from the shower before it gets out of the bathroom, likewise for the extractor in the kitchen. Check that all fans do vent outside rather than into your loft, best to check you get feel the air coming out of the outside vent, as there may be a hose not connected.


Sounds like your new windows are much better than your old ones, and the house is now much tighter than it was. This is a common problem in well sealed houses. We have Anderson double pane low E windows, and they fog up inside when we boil things on the stove in the winter. The best solution is natural ventilation. Try leaving the window open a crack behind those heavy drapes. We have a fairly powerful kitchen vent fan, and I keep the fireplace air inlet open a bit all year to provide replacement air. You do want to solve that fogging problem because that excess moisture could start rotting your new windows; unless the are vinyl clad.


Windows don't cause condensation. Warm air holds more moisture than cold air.The air in your house is warmer in the center of a given room. As the air moves toward the outer walls of your house it cools holding less moisture. Your window glass cools faster than your walls do (walls also absorb moisture but glass doesn't) so you see the effect on the window glass first. It's also in your plaster walls and possibly in the insulation inside your walls. Cold air leaking in around your windows will also cool the existing air and form moisture on your windows.

You can have this checked by a professional. Might be cheaper than new windows. Storm windows can also help but remember they can also fog up in between the storm window and the regular window. Consult a specialist, not a window sales person. Those not making a living on selling windows.


Quite simply your home is now warmer than before. No air gaps around windows. You'll notice it's only in the bedroom and en suite bathroom.

Your body puts out this moisture at night and your new windows are highly efficient.

All is good.

Don't worry.


You asked "Is it likely that there's a draft around the windows keeping the windows cold?" and the answer is that it's the opposite! You have lost the draughty old windows which had enough ventilation to prevent condensation.

The answer is nearly always: More heat and/or more ventilation.

Oh, and watch any activities you do indoors which creates moisture. Had one client who insisted there was a problem in her utility room only to find out from another house member that she spent hours in there ironing with her gigawatt steamer iron system...

And another (from abroad somewhere) who used to steam food from her home country for hours on end...


My guess is that the frame isn't well-insulated or the windows aren't two-paned.

Condensation is caused by things being cold, so what you basically need to find out is why the windows are cold.


I recommend getting a humidistat or hygrometer to monitor the humidity in the house. The colder it gets the less humidity you want in the house, because of the condensation problem you describe.

Here is a list of humidity levels based on temperature:

Outside Temperature, Indoor Humidity

  • -10F, 20%; 0F, 25%; 10F, 30%; 20F, 35%; 30F, 35%

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