Why do I have SO MUCH condensation on my windows!?

This is a great time of year to talk about indoor moisture.

Because we keep our houses more closed up in the winter (unless you live in an area that needs a lot of air conditioning and you keep the house closed up year round) moisture can build up in the warm indoor air. Warm air can hold moisture until it reaches saturation and then it will start to give up that moisture to the cooler surfaces around the home.

Take for example this metal screw that attaches the front entryway door pull handle to the face of the  door.  The staining and moisture is because there is way too much moisture in air at the interior of the home and it is condensing on the cooler metal.  It is bad enough that water runs down and stains the door.


While a little fogging of windows is normal during incidental “steamy moments” like when you do the dishes (does anyone besides me really do dishes by hand?).  If you have condensation on your windows to the point that it starts to run down the glass–YOU HAVE A MOISTURE PROBLEM!

Your windows certainly should NEVER look like the one in this picture–all that moisture and mold is in the living space–not between the panes of glass.


You don’t really have to wonder if you have a moisture problem when your windows look like this–you do have a moisture problem. The next thing will be figuring out why and then doing something about it.

There can be SO many causes of excess moisture in a home that it will not be the purpose of this post to go into great detail about the many causes. This post instead will be about what you can try before you call in the big guns to figure out what has gone wrong with your home.

In the majority of cases it is not the house that is the problem at all–it is the occupants of the home and the fact they do not know how to properly operate the home. Some people’s lifestyles are more problematic than others. If you diligently do the things I suggest and the problem does not go away–then you will likely have to consider other causes that are more related to problems with the house itself.

1. Open curtains and blinds at least a little bit every day. While it may waste a little energy, you don’t want the air that gets trapped behind the curtains to give up its moisture to the cold glass. Adequate circulation of air will prevent this. Condensation is especially problematic in bedrooms that people tend to keep cooler and tend to keep curtains drawn tighter for longer periods of time. Anyone that has slept in a tent in the cold is aware of how much moisture our bodies give off when we are sleeping.

Keeping the entire interior of the home at close to the same temperature is recommended as rooms left unheated will collect the moisture out of the surrounding room’s warm air like a magnet.  Because it cannot hold the moisture, it will store it on the windows and the cold walls behind all the storage boxes in the room. For example if you have block-out blinds or Venetian type blinds–leave them raised an inch or two to allow for air flow to the glass.

Take a look at these two pictures.  Same room, same humidity and temperature levels.  The first one is the results of condensation with the blinds closed, the second one with the blinds open.



While there is still a little bit of condensation of the glass, consistent with moisture levels being too high, leaving the blinds open prevents a worse build-up of moisture.

2. ALWAYS, run the bathroom exhaust fan for at least an hour after every shower. If you have a way of warming the bathroom into the upper 70’s for a few minutes prior to taking a shower, the warmer air will hold more of the moisture from showering and can then more easily be exhausted during and after showering. If you have condensation running down your mirror or the bathroom window after showering, you are not using your bathroom properly. And another thing–get rid of those dang water saver shower heads that atomize the water making the water easier to disperse into the air. There are other types of water saver shower heads.

3. ALWAYS, use the kitchen range hood while cooking and for a few minutes after cooking. Always use the kitchen fan when the dishwasher is running or even while you are washing dishes by hand.

4. No Grow-ops in the house—legal or otherwise. A few house plants will not cause a problem if all other things in the home, including the inhabitants, are behaving properly.

5. Make sure the laundry exhaust fan is used while doing the laundry. If you don’t have a laundry fan–consider having one added.  Modern construction would require one. Another thing about the laundry is that if the exhaust duct is restricted enough to increase drying time, more dryer moisture will find its way into the home. Making sure that the dryer is behaving properly is important in maintaining proper moisture levels in the home.

6.  Don’t hang laundry to dry indoors.

7. Make sure that all exhaust fans are functional–just because they turn on and make noise does not mean they are doing the job they are there to do. A simple test is to cover the entire grill with tissue and see if the fan uniformly holds the tissue in place. Make sure you do this test with any doors to the room closed. Doors with inadequate clearances for air to move into the room as the air is exhausted may render the fan non-functional. Improving clearances may be necessary. Another test is to put the tissue on the floor near the bottom of the closed door and then turn on the fan–the tissue should be forcefully sucked into the room away from bottom of the door.  Really tight homes may want to think about whether the whole house has adequate means of bringing fresh air into the home when exhaust fans are operated.  All of this can be further complicated by not having direct vent gas appliances.

8. If you are going to cook and bathe in your home it is imperative that you maintain an indoor air temperature above 65 degrees F. I know we all have energy consumption considerations but if you keep the home at 64 degrees (or areas of your home at 50 degrees) and save $200.00 a year in heating costs and cause $2000.00 in water damage you have not accomplished much in terms of saving money. Health costs may also be affected as keeping homes cooler may result in poor indoor air quality conditions.  This cost/benefit ratio is even worse if we are talking about keeping isolated portions of the home cooler. Just heat your home–it will reward you for it.

So, try these things–if you still have nasty looking windows like in the picture above–call a qualified home inspector or indoor environment specialist to figure out what is going on.

By Charles Buell, Real Estate Inspections in Seattle

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  1. Hello Charles very good topic this time of year. You probably left it out on purpose but HRV’s are used in new builds more these days. Some jurisdictions have them in the codes. I’m finding that even my installer has limited knowledge of HRV’s. What’s your take on them.

    From Doug

  2. My eyes got moist just reading this. Good points!

    And I have never seen a laundry room exhaust vent in my life or inspection career, and did not know they exist. In my house the laundry room is dead center and beside the garage. I don’t know how one could be installed even if I wanted it!

    • Charles Buell says

      Laundry exhaust fans have been required in WA State for quite a while. No matter where the laundry room is in a house it will have joists that cross it that run to the exterior wall of the house. Very easy to install—no different than a central powder room or bathroom.

  3. Mayhap! But as I said, until this post I never knew they existed!

    Given the structure of my house, it would not be “very easy to install” in our laundry room, having to cut through 12 or 15 floor I-beams! And the tubing would have to be over 30′. Methinks the cost/benefit would be way out of whack…

  4. You would have to see the house. One direction would be into the garage wall (not ceiling) with a bedroom overhead with joists in the other direction. The other way would be a hallway which abuts the staircase from the third level to the basement.

    Of course, I did have that post about regulating away staircases in favor of fire poles, because it would save the number one source of household accidents. Super idea – a Billy Jays original. Now, yanking out those stairs I could indeed put in the now-much-touted laundry room vent (which nobody, and I mean nobody, else in the area would have). When you are the only one with something, you are indeed special!

    • Charles Buell says

      Gotcha Jay, that would all get handled at the design stage and it would be spelled out on the plans how the venting would run. It would get figured out because it is required. Obviously retrofitting older homes can be problematic for sure.

  5. One thing I noticed an awful lot this summer, which could be contributing to some people’s poor ventilation, is paper wasps building nests in the hood of the exhaust fan covers which severely restricts the outflow of air from bathroom fans terminating through roof decks. Seems they made the screen the perfect size for these guys.


  6. I wish I wish that I had read this when we lived in North Dakota! Having lived in the Willamette Valley most of my life, severe cold was really new to me. I never felt good from the moment we moved into the house, but when it started getting cold, things got bad. I also started to notice that the condensation was so bad it FILLED the whole window track! Not knowing what to do, I ran every vent fan day and night and wiped up/out the water every morning, drying the microfiber rags in the dryer each day. I asked my husband who had grown up in Alaska if this was normal. Offhandedly he assured me his mother always did this. Note to self: double check with mother-in-law sooner. Long story short, our air exchanger was not functioning at all! The problem was that even with the air exchanger fixed, it was only better, not great. That I where I learned the importance of a well built house. If I had to do things all over again, I would pay to have a building inspector look at my house, even though we were renting. I could have at least found out what all was wrong with it and maybe fixed some!

    • Charles Buell says

      If you are having so much condensation at the windows that the track is filling up with water, there is something wrong with the way the house is managing moisture. Call a qualified Building Performance professional to sort it out.

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