For double pane windows, this is the seal that separates the two panes of glass and holds in the air or gas that resides between the panes. You can tell that a seal is broken if moisture has entered the cavity between the panes resulting in fog or water streaks on the inside of the glass, rust at the bottom inside the pane, or the traces of past moisture in the form of dry drip marks or streaking.
In Colorado, double pane windows are quite common due to their insulation benefits. During an inspection I sometimes find at least one double pane window with a broken seal. Usually on the south side of the home where the sun does the most harm.
This can be somewhat unsightly, but does the window need to be replaced? Well, that’s a judgement call.
Most of these windows are filled with Argon gas, which is a better insulator than air, but only slightly. The insulation value of plain air between the panes of a window is about R2. With argon gas intact, the insulation value is about R3. To put this in perspective, the walls in your home are likely insulated to an R9 to R12 value, and your attic should be insulated to R38 (in Colorado).
The “R” in R value stands for Resistance, or Thermal Resistance. The higher the number the better the unit or material resists the transfer of heat. For instance, resisting heat transfer from inside your home to the outside in winter (keeping you warmer), or heat transfer from the outside to inside in summer (keeping you cooler). So even though the window may have a broken seal, the R value doesn’t change that much. Yes it is a 33% decrease (from R3 to R2), but an R value of 3 to begin with is not that significant.
So should the window pane be replaced? It’s your call. Energy efficiency may not be the driving factor. Visibility, or the lack thereof, could be.
Also, only the glass double pane itself need be replaced. Not the entire window with frame and all. Most window panes can be removed and replaced for only a few hundred dollars including labor.
Here are some helpful links if you want to learn more about window options and their energy saving properties.
Is it a worth the extra cost to buy windows filled with argon gas? Click Here
Compare Thermopane Windows (multiple panes, argon gas, krypton gas, Low-E) Click Here
