Do Frosty Windows Need Replacement?

We’ve all seen it: condensation gathered on our windows, dripping onto the window frame and sill. If it is cold enough outside it can quickly turn to a frosty, icy scene. It may be pretty, but it can cause serious damage to window components, walls, and insulation. Time to replace those windows, right? Not necessarily.

Window condensation problems can have several causes, but the primary reason is fairly simple: more moisture than the air can hold at the cold surface of a window. Just like rain, fog, or snow, when the air temperature gets low enough the water has to condense somewhere – and your frosty window is the result. But is the window frozen because it is leaky and cold, or is there too much moisture in the air?

There are three basic things to do before spending money on new windows: control moisture production, tighten and insulate, and ventilate.

Control Moisture Production
The easiest (and most inexpensive) way to address frosty windows is by evaluating your indoor humidity levels. For about $30 you can get a simple hygrometer that can tell you the humidity levels in your house. The proper indoor air humidity for winter is somewhere between 15% and 40%, depending on the outside air temperature – the warmer it is outside, the higher it can be. Anything over 45% indicates excess moisture in the house.
 
There are many origins for high inside humidity and they can add up to significant quantities in combination. Among the sources are:

  • Human activities, including cooking, showering, washing and drying clothes, inside firewood storage, humidifier usage, numerous houseplants, and simply breathing.
  • Faulty appliances or equipment, such as unvented heaters or clothes dryers, blocked chimneys, insufficient combustion air for furnaces or water heaters, plumbing leaks, or inadequate or improperly installed kitchen or bathroom vent fans.
  • Improperly adjusted systems, such as humidifiers set too high.
  • Moisture infiltration, through ground water seepage, poor foundation drainage, or leaks in roofs or walls.

Seal Air Leaks and Insulate
Although a little more expensive than reducing moisture production, tightening up your home can reduce window condensation problems and can pay real dividends in lower energy bills.

If there is not enough attic insulation, or if there are air leaks around plumbing or electrical wires entering the attic (attic air leaks) heat can flow out through the top of the house, drawing cold air in at the lower levels, even through windows and doors that may be relatively airtight. Gaps around window panes, poor or missing weather stripping, or inadequate caulking can all lead to window and door units that permit cold outside air to leak air in or out, cooling them sufficiently to permit condensation to form. Air leaking through the top of the house may also be drawing moisture up from the basement.

After the attic is adequately insulated and attic air leaks are sealed, windows and doors can then be sealed with new caulking, weather stripping, or by applying shrink wrap on the interior side or heavier plastic on the exterior. If windows need more repair, there are refurbishing options (like insulated sash replacements) that are somewhat less expensive than complete window replacement.

Provide Proper Ventilation
After reducing the sources of moisture, sealing air leaks, and insulating, you may still have condensation or frost on your windows. Homes that have been well-insulated and tightened up have fewer places for air to move freely from the inside to the outside. This is good for controlling heat loss, but it also traps moisture inside the house, increases indoor air pollution concerns, and contributes to those iced-up window panes.

Ventilating the living space may be the next project to tackle. Bathrooms and kitchens usually have vent fans to remove moisture and indoor pollutants, but unless you have a source for fresh air to balance what was exhausted, air can be sucked down chimneys, interfering with the safe operation of your furnace or water heater. Vent fans should not be run for more than 15 minutes or so; after that they are removing mostly heated air.

So, if you are experiencing wet or frosty windows, try reducing your indoor moisture levels, insulating and sealing your attic, sealing up the windows you already have, or installing ventilation systems. You may not need new windows to take care of your icy winter panes.

For more information, go to the Energy Info Center link at the Minnesota Department of Commerce website: www.energy.mn.gov or call 800-657-3710.

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