Instructions – Correct Installation of Capillary Tube

Definition

A capillary tube (also known as a “breather tube”) is a narrow tube inserted into the spacer between the two panes of a dual-pane window. Its purpose is to equalize pressure between the inside and outside of the sealed unit.

This is especially important when shipping by air freight, as air pressure decreases at higher altitudes. It is also crucial when transporting dual-pane units to high-altitude locations.

You can find the capillary tube extending from an outer corner of your dual-pane window unit.

Vertical Installations

Your windows are delivered with open capillary tubes, which must be sealed before installation. Follow these steps:

1. Apply silicone sealant in mild weather (50–70°F).
2. Seal the tube by applying a drop of silicone sealant to the opening.
3. Keep the window unit standing vertically.

Ensure the capillary tube is positioned at the top of the window, pointing downward. Do not install the window with the tube at the bottom.

If the tube needs to be cut for installation, steps (1), (2), and (3) still apply.

Important: Capillary tubes must be sealed within 10 days of receiving the window.

Horizontal/Sloped Installations

The same instructions apply for dual-paned horizontal (e.g. skylights) or sloped installations as for vertical installations, though position of the tube at installation is not critical.