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question about high elevation capillary tubes in new windows

As some of you know, I'm in the final stages of designing my next home. The site is at 4,400' elevation so some of my windows must have capillary tubes. That's something I always check for clients who live at elevation but this is the first time I've had to deal with it personally. Fortunately, most of my windows are large enough to not require tubes at my elevation (larger IG units are naturally more tolerant of pressure changes).

This technical document from Cardinal (Cardinal makes the IG units for my windows) explains difference between capillary tubes and the much larger breather tubes that some window manufacturers use. In particular, it says capillary tubes cannot be sealed. Apparently, breather tubes are designed to be sealed at the site.

Although the impact on u-value is relatively small, I'm concerned that cap tubes could lead to internal condensation. I'm sure many of you have seen how windows with failed seals develop ugly stains/haze over time from condensation cycles. The Cardinal document seems to gloss over this...
Capillary-tubed units are designed for the purpose of relieving pressure associated with high altitudes, that is, mountainous areas typically with low humidity. Installation of a capillary-tubed unit in any other environment may significantly reduce the longevity of the unit. Because of the reduction in unit longevity, Cardinal IG recommends only installing capillary tubes in high altitude applications, and minimizing the use of capillary tubes whenever possible.
This is NOT comforting. Yes, it's dry here but dew points approach the interior cooling set-point during our seasonal monsoon.

Anyone have experience with windows with capillary tubes?


  • David ButlerDavid Butler Posts: 3,889
    I just spoke with an engineer at Cardinal IG. He said moisture staining is unlikely to occur with cap tubes, especially in my area, since the tube ID is so small (a few hundred microns).

    It's not because the moisture can't pass but, as noted in the above linked document, the small tube diameter and long length act to slow down (dampen) the exchange rate. Equalization at the site takes on the order of 48 hours. After that, local pressure differentials are relatively small in comparison, thus reducing moisture migration to the point that it can easily be absorbed by a desiccant installed within the IG unit.

    I still hate giving up a few points of u-value since windows with cap tubes don't get argon fill.
  • David ButlerDavid Butler Posts: 3,889
    Turns out I may not need cap tubes after all. So far, Andersen is the only manufacturer I've looked at that requires cap tubes below 5,000 feet for some of their windows. Since close to half of my windows would require cap tubes above 4,000 ft, that may be reason enough not to go with Andersen.

    OTOH, anyone building a home at a higher elevation may benefit from their method of stipulating cap tubes restrictions by size and elevation. Some of Andersen's larger units can be ordered with argon up to 10,000 ft!