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?