Which Low-E Coating Suits Austin Summers

On a house that sees ninety degree highs on well over a hundred days a year, the coating on the glass matters more than the frame it sits in, and the running record window replacement austin fish tommy holds shows the same pattern on every street from Tarrytown to Mueller. A replacement window in Austin, TX gets judged by how much afternoon sun it keeps out of the room, and that is a coating question first.

What the coating does to the glass

A low e coating is a layer of metal oxide thinner than a hair, laid on one surface of the glass inside an insulated glass unit. It reflects long-wave heat while letting visible light through. Two panes with the coating on the right surface behave very differently from the same two panes bare. The coating faces the gap, never the room side of the inner pane and never the outdoor face of the outer pane.

Soft coat and hard coat

Soft coat low e is sputtered on in a vacuum chamber and sealed inside the unit. It is the stronger performer for blocking solar heat gain, and it is the usual choice for a hot climate. Hard coat is baked onto the glass while it is still hot, so it is tougher to handle but lets more heat through. For a sunny Texas wall, soft coat with a low shgc wins almost every comparison.

One layer or several

Single-silver coatings cut some heat. Double and triple silver stacks cut a good deal more and still look fairly clear. The stacks differ in tint as well: some read faintly blue or green when the sun hits the glass at an angle. Holding a sample against the existing glass on the sunniest wall shows the tint better than any spec sheet.

Where it goes on each window

On a double hung, both sashes carry glass and both need the same coating, or the two halves look mismatched from the street. A picture window beside a casement should match both.

Frame material changes the result

A vinyl window and a fiberglass window both hold the glass steady, but a dark clad window or an aluminum window with no thermal break conducts heat around the glass, and the coating cannot fix that. A composite frame or a wood window with exterior cladding stays cooler to the touch on the south and west faces. The coating handles radiation; the frame handles conduction, and both show up in the same summer bill.

What the label should say

Every unit carries a label with a u factor and an shgc. For a sunny Austin wall the shgc is the number to push low, while the u factor can stay moderate because winter rarely lasts. A low e coating with an argon fill and a warm edge spacer rounds out a unit that stays comfortable in July and does not sweat at the edge during the occasional freeze.