Triple Threat

High-performance windows as easy as 1, 2, 3

People of a certain age may remember the memorable scene in the 1984 mockumentary “This Is Spinal Tap,” when the daft rocker Nigel Tufnel thinks his guitar amp is louder than anyone else’s because his dials go up to 11, not 10.

It’s tempting to ponder “Spinal Tap” when you think of triple-glazed windows, the newfangled technology that’s seen as the future of energy-efficient glass openings. But are the windows just another version of a dial that goes to 11?

Triple-glazed windows feature three panes of glass and have all the other well-known, high-performance attributes and features: low-E, gas insulation, warm-edge spacers and films. The windows are said to be ideal for cold climates because of their resistance to heat loss, but some manufacturers claim the products are also effective in warm regions.

Now making in-roads in the U.S. market, triple-glazed windows will soon become the norm. The EPA just upped the standards for 2013 windows that want the Energy Star certification, so products will have to meet new performance criteria for U-factor — the rate of a window’s heat loss — and solar heat gain coefficient (a.k.a. SHGC) — which measures how well they block heat from the sun.

But triple-pane windows are pricey, costing about 25% more than double-pane units, and some wonder if they are worth the premium. Fortunately, window performance is relatively easy to measure and to calculate for return on investment.

“Adding a second or third pane of glass has substantial effects on window performance,” said Florian Speier, founder of Zola Windows in Boulder, Colo.  “For example, using Zola Windows’ U-values, triple-glazed units have twice the performance of double-glazed units. Whereas double-pane offers about a five-fold performance increase over single-pane.”

Said John Lewis, head of code and regulatory affairs for Simonton Windows in Columbus, Ohio: “If the consumer is after the very best thermal performance, then triple-glazed units are the clear choice.”  

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