How do I prevent condensation on my windows? (Windex-edition)

October 25, 2018 10:00 PM

I cleaned my dirty windows with Windex during the daytime. They looked great. Now it's night time and my windows are all fogged up and streaky! Why and how do I get rid of it?

I tried to wipe the condensation away thinking it still had Windex residue but it comes right back. My thermostat says room temperature is 70 degrees with 60% humidity. The bathroom is located at the opposite end of the apartment so I do not think that would cause a spike in humidity after a shower. The windows never fogged up like this before I cleaned them. What can I do to fix it?

posted by joeyjoejoejr to Home & Garden (10 answers total)

It probably helps to understand why condensation happens, if you don't already. Humidity is water in the air. Indoors, some of that water is just there (same % as the outside), and some of it comes from people breathing, cooking, drying clothes indoors, burning gas (if you have it), and using hot water (showers/baths). When that water vapour in the air hits a cold surface, it cools and turns from vapour to liquid, forming condensation droplets. This is why cars use an electrical heater to warm the windows and turn the condensation back into water vapour suspended in the air.

So, realistically, your three main fixes are:
1. Vent the air in the apartment (using extractor fans, or opening door and windows),
2. Reduce the amount of water you're adding to the air (see above),
3. Reduce the humidity artificially with a dehumidifier.
4. Raise the temperature in your home to cause the windows to warm (assuming your windows are well-insulated - otherwise you're just wasting a lot of energy)

There are probably ways to make the condensation droplets 'stick' less to the windows, but all that means is a puddle on the windowsill, so not ideal.
posted by pipeski at 1:55 AM on October 26, 2018 [1 favorite]

Best answer: When your windows were dirty, the condensation most likely formed a film and did not show so much. Now they're clean, and the surface tension is no longer being lowered by the dirt, and so now droplets form on the clean glass. They are much more visible than an even film.

If this is the beginning of heating season where you are, it's understandable that your windows will steam up more now; that should stop once the air inside gets drier. More information here.
posted by Too-Ticky at 2:00 AM on October 26, 2018 [3 favorites]

The bathroom is located at the opposite end of the apartment so I do not think that would cause a spike in humidity after a shower.

If your bathroom isn't being vented by an extractor fan for at least ten minutes after your shower, I can find lots of reasons to disagree with that assessment.
posted by flabdablet at 2:10 AM on October 26, 2018 [2 favorites]

Best answer: Try this: rub a bar of soap on the window. You don't have to cover the entire window; just get a bunch of streaks on it. Then use a clean cloth to polish it clear. It's an old diver's trick.
posted by Kirth Gerson at 3:39 AM on October 26, 2018 [5 favorites]

I've also heard using newpaper (old school newsprint) instead of paper towels leads to streak free glass
posted by exparrot at 5:27 AM on October 26, 2018

Seconding bar of soap on the glass, or shaving cream if that's easier to apply.
posted by JoeZydeco at 7:41 AM on October 26, 2018 [1 favorite]

60% is a very high indoor humidity reading. If you have exterior venting (bathroom or oven) you need to run it. Below 50% is recommended.
posted by The_Vegetables at 9:14 AM on October 26, 2018

Seconding the use of the 'invisible' plastic film. You put it up, and then heat shrink with a hair dryer. Can't hardly tell if it's there.

We have all new windows on the house except for the french door, which is a heavy single pane. I put the film on (looks at watch) just about this time of year to prevent condensation and heat loss. Works like a champ.
posted by BlueHorse at 7:30 PM on October 26, 2018

Many people find using newspaper to clean windows helps with streaks. You can use newspaper when they are wet with condensation, at this point you don't need any more Windex.
posted by theora55 at 9:03 AM on October 27, 2018

Came for the soap thing. Same thing you can do with bathroom mirrors. You wipe them down with shaving foam and magically they don't fog up nearly as much. (Then you just end up getting one of those heated no-fog mirrors for the shower and don't bother.) Windows are *too* clean.
posted by zengargoyle at 1:08 PM on October 27, 2018 [1 favorite]