Murphy Brothers Blog

Cold MN Days: Condensation on inside of windows???

We recently installed some new Low E, Argon windows for a client (a second project for them), which increased the energy efficiency of the home. The homeowner emailed asking about condensation on the windows on our cold Minnesota days. I thought I might post my response, as I have had a few questions on this over the years.

 “Basically any relatively air tight home (like yours) will get condensation on the windows on a brutally cold night. Older (draftier) homes don’t usually have this issue. Controlling your relative humidity in the home is the best way to manage it….which you can control through that humidifier you have and by monitoring the amount of humidity household activities add to it. The usage in your home adjusts that humidity…so when you take nice long showers/baths, you will want to run the bath fan for a good while. If you hang up laundry to dry, boil water without venting or have lots of plants, they can also add humidity to your home. I also get ice and condensation on my windows on really cold days as well…and I need to turn the humidifier all the way down on those cold days for it to dissipate. It is good to keep the water/ice off the windows. Also, you probably already know….but keeping air flow to the windows is good too. Sometimes windows are covered all the time and the condensation and lack of air flow to them can build up mold on any wood jambs. Blowing air over the interior glass acts just like a car defroster does…so air circulation is good (ceiling fan or setting the furnace on “Fan” for periods of time). The temperature of the inner glass surface is at or below the dew point for the amount of humidity in your inside air. The humidity of your indoor air is quite possibly much higher now with your new windows because the air leaks around your old windows were eliminated once the new windows were installed. Cold, drier air that leaks into your house from the outdoors lowers the relative humidity indoors. This is one reason people have static electricity problems in drafty homes during the winter months. Dry air makes it very easy for the static sparks to transfer from your hands to grounded objects.

You can purchase a decent hygrometer for under $50.00 if you want, it is a tool will allow you to get accurate readings of indoor humidity. You can do daily readings and then look around to see if you have things that add too much water to the air. Minimize the number of indoor plants you might have. Run kitchen exhaust fans if you boil lots of water when you cook. Be sure to operate bathroom exhaust fans during bathing activities. Those types of things will help manage it. So, yes, it is normal to have the ice build up on a cold day, but do what you can to get it off the windows so you protect your investment.

Hope this helps. :)”

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