Your question does not have an easy answer but I'll give it a shot.You may already know the following but I'll include it for those who don't.
- Condensation happens on a surface when the temperature of that surface is below the dew point of the air next to it.
- The dew point is the temperature of air at which the humidity is 100%.
- As the temperature rises, the humidity drops. As the temperature falls, the humidity wants to rise but can't because it's already 100%, so the excess water vapor settles out as liquid water on any cooler nearby surface.
- Another way to say this is that cold air can hold less water vapor than warm air.
Two ways to reduce condensation
There are two ways that you can reduce the amount of condensation forming on a window:
- raise the temperature of the window surface (a warmer surface is less likely to be below the dew point of the adjacent air) or
- reduce the humidity in the interior air (lower humidity has a lower dew point).
Raising the temperature of the surface of your storm window is relatively impossible without turning down your furnace and putting on a sweater, so that leaves lowering your indoor humidity.
Lower your indoor humidity
Look at where you might be generating moisture inside your home:
- showering without a fan running,
- boiling water,
- a broken dryer vent.
To the extent that you can, reduce the amount of water that's evaporating inside your home.
If that doesn't help, you need the services of a professional Energy Auditor who can find routes where outside water may be getting inside your home.
- As counter-intuitive as it is, air sealing your home - plugging all the little holes where air gets in and out - can lower your interior humidity.
- This particularly helps when your condensation problems are caused by air entering from a damp basement or crawlspace.
Good luck, and come back and tell us what you've found that works.
We're all still learning and I'd love to hear about it if you solve this problem.
For more information:
Read "Our aluminum-frame windows are harboring condensation and mold. Can you recommend window solutions for a damp environment?" a Q&A answered by Steve Saunders.