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How To: Eliminate Window Condensation

window condensation

In the winter, condensation on windows is a common issue most of us face. It’s especially prevalent on single-pane windows, but double-pane windows are not immune either. Window condensation doesn’t have to be something you simply accept because there are ways to fight it.

Stopping it completely may not always be possible depending on your individual house and windows, but in this post I’ll lay out a few steps you can take to dramatically cut down on, and in some cases eliminate, window condensation completely.

What Causes Window Condensation?

You’ve heard of the dew point right? Well, in every house in the winter the dew point is at work in the exterior walls of your house and that includes your windows which are the most visible.

Warmer air can hold more moisture than colder air. That’s why when you fill a glass with ice water it always sweats unless you’re sitting outside in subzero weather drinking ice cold lemonade like an insane person. The cold surface of the glass causes the air immediately around your beverage to drop its moisture as it quickly cools down.

The same thing happens in the winter on your windows. When it’s 20ºF outside and inside you’ve got the thermostat sets to 68ºF the dew point will be somewhere between those two temps. The glass on your window will inevitably be the coldest surface on your walls and once the warm moist air inside hits that cold surface it drops its moisture in the form of condensation. Isn’t physics annoying sometimes?

Scarily enough this same process can be happening inside your walls at the same time because somewhere between your drywall or plaster walls and the siding on the outside the temperature crosses that dew point and condensation occurs. That’s why understanding water vapor and its potential issues with insulation and mold growth is imperative before retrofitting insulation into any old house.

How To Eliminate Window Condensation

Now that you understand the physics of condensation how can we work to eliminate it? There are a few ways to solve the problem of window condensation and we’ll dig into all of them. You may not be able to accomplish all of these but you can certainly do some of them to help resolve the issues you are facing.

1. Lower Humidity Levels

The main thing you should focus on is the humidity level inside your house. It will never be a completely arid climate inside your house, but you can do quite a few things to help keep humidity at a healthy level.

According to the MayoClinic the ideal humidity level inside a home is between 30-50%. Anything above or below that can cause issues either in your own health or the health of your home. A humidity level of 40% would mean that at a particular temperature the air is holding 40% of the moisture it is capable of holding. Remember that as temperatures drop the air can hold less moisture so 40% humidity at 80ºF means there is much more moisture in the air than 40% humidity at 60ºF.

Smart thermostats like the Nest Learning Thermostat can track your humidity levels inside so you can see how your house measure up. Tracking this on days when you notice condensation is a great way to track down potential issues.

Ways to Lower Indoor Humidity

  • Get a Properly Sized HVAC – An oversized HVAC system will not run often enough to keep humidity in the proper range because it will run for such a short time. An undersized unit will wear it self out running too long but it won’t have the same issues with humidity control.
  • Upgrade to a Dual or Multistage HVAC – Dual stage or multi stage HVAC systems are better at keeping humidity levels low because they can run for longer periods at lower power usage which maintains more consistent temperatures and humidity levels.
  • Install a Dehumidifier – Whether it’s a whole house humidifier hooked up to your home’s HVAC system or just a small room dehumidifier or two in moisture prone rooms these can help keep that mugginess at bay making your home more comfortable and less prone to condensation.
  • Utilize Vent Fans – Bathrooms and kitchens generate a lot of steam and humidity that disperses throughout the house. Using a bath fan or range hood to suck the hot moist air up and out of the room and keeping it on for about 10 minutes after your shower removes the moisture before it ends up on your windows.
  • Use DampRid – The simplest and most low tech solution is hanging some DampRid in areas that need drying out or that don‘t get good airflow like near hampers, closets, laundry rooms, under sinks, etc. This product sucks moisture out of the air and when it’s lived it’s life you thro it out and hang a new one.
  • Open Your Windows – Not every day has beautiful weather, but when it’s a dry day open up your windows and let that stale, muggy indoor air outside while inviting fresh drier air inside.

2. Open the Curtains

When you open up your curtains you allow more airflow to get to your windows which will carry away any condensation that has formed. If you have interior window treatments like curtains, blinds, plantation shutters, or something else constantly covering your windows then that condensation just sits without a chance to dry out.

Waking up to foggy windows isn’t always a problem if that condensation can be dispersed quickly by getting some air flowing over your windows. That way the windows can dry out and not create bigger issues like peeling paint or wood rot.

3. Install Storm Windows

Installing storm windows is a fantastic and cost effective way to really up the efficiency of your single pane windows. Storm windows are not a one size fits all product anymore. There are interior storm windows and exterior storm windows. Operable metal storm windows and historic wood storm windows.

The variety of storm windows on the market today is so vast that there is a good option for almost anyone. I’ve written a pretty thorough post on how to choose the right storm window so please do check that out here.

Adding that extra pane of glass or plastic will make a big difference in keeping that glass temperature moderated. If you can moderate that temperature enough to keep it above the dew point then condensation solved!

4. Turn The Thermostat Down

Not only will you save on your heating bill, but like we discussed earlier cooler air can hold less moisture. 40% humidity at 70ºF means approximately 35% more moisture is in the air than 40% humidity at 60ºF. The more you can lower the temperature and maintain the humidity the lower your chance of condensation.

That may mean you need a couple extra blankets to keep warm. The trade off may not be worth it but that depends on you.

Wondering what temperature and humidity you need to achieve to stop condensation on your windows? Try this dew point calculator and play around until you find your goal temperature and humidity.

5. Light a Fire

I know I just told you to turn the thermostat down, but hear me out. Cranking up your fireplace, while it can warm up the room also draws moisture out of the air better than most other heating methods, especially steam radiators or boilers.

Keeping a fire burning in the fireplace can both warm up a room and decrease the humidity indoors which in the battle against condensation is a major win. Anecdotally, I have noticed in my own house that on winter nights when the windows are filling with condensation our living room windows stay bone dry when a fire is roaring.

What Should You Do?

In the end condensation can be eliminated to the extent you are bothered by it. Doing just a few of the things listed above will definitely help you resolve some of the condensation issues you’re facing. Really focusing on them in a big way can make huge gains. We all have to find that balance to remove as much condensation as possible, but still maintain our sanity.

Replacing your HVAC system is probably not in the cards, but the next time you are due for a replacement system make sure it is sized properly and consider those dual or multistage systems. The use the other tricks you’ve just learned as you best can to beat back that window condensation.

Good luck and stay dry!

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1 thought on “How To: Eliminate Window Condensation

  1. One of my main areas with a condensation problem is on the inside face of storm windows on 1915 double hung windows. Some storms are traditional, others are metal triple track replacements. I’ve been sealing gaps around the weight pockets, etc. and putting spring bronze weatherstripping around sashes. They some still fog up/frost over. All on the inside of the storm. Where this moist air is coming from eludes me so far.

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