Energy efficient windows in Utah.

Start with the U-Factor

The U-Factor measures how fast a window lets heat escape. Lower is better. On the NFRC label it runs from about 0.20 to 1.20, and the windows worth buying for a Utah County winter sit near the bottom of that range.

Both Utah window rebates draw the line at 0.22. Rocky Mountain Power's Wattsmart program and Enbridge Gas ThermWise each require a U-Factor of 0.22 or lower, and ENERGY STAR uses the same 0.22 ceiling for its Northern climate zone. A window rated 0.23 can look identical on a sample board and miss every rebate.

How a window gets to 0.22

• Low-E coatings. A microscopically thin metallic layer on the glass that reflects heat back into the room in winter. The U.S. Department of Energy points cold-climate buyers to gas-filled windows with low-E coatings.
• Gas fill. Argon or krypton sealed between the panes, which slows heat moving across the gap.
• A third pane. Triple pane adds a second sealed gap. Many of the windows that land well under 0.22 are triple pane. They weigh more and cost more.
• The edges and the frame. Heat leaks faster at the edge of the glass and through the frame than through the middle of the glass, so the spacer and the frame matter as much as the glass.

Some double-pane windows reach 0.22 with an extra coating on the room-side glass. Others need the third pane. The label settles it.

Double pane or triple pane in Utah County

Triple pane earns its cost on the exposed spots: bench lots that take canyon wind, big west-facing glass, bedrooms on a busy road, and rooms that never match the thermostat. In Lehi, Highland, and Alpine, the lots near the canyon mouths and the Point of the Mountain are usually where it pays off first.

On a sheltered lot with modest windows, a double pane that meets 0.22 is often the better use of the money. Either way, get the U-Factor of the exact window on your quote, in writing. If the number is not on the quote, you do not know what you are buying.

Frames: vinyl and the alternatives

Vinyl frames insulate well, never need paint, and come in a wide range of sizes, colors, and prices. Heavier-wall vinyl holds its shape better in large openings and on windy lots. Fiberglass and wood-clad frames cost more and suit some homes, especially older ones where the look matters.

Tilt-and-turn windows in Utah

Tilt-and-turn windows are the European style. Turn the handle one way and the top of the sash tilts in for air. Turn it the other way and the whole sash swings into the room like a door. The locks pull the sash against the gaskets at several points, so they seal tight, and both sides of the glass clean from inside the house.

Because they swing in, plan around blinds, furniture, and deep sills before you order. Not every window line offers them, so ask early if you want them, and get the U-Factor in writing like any other window.

How to read the NFRC label

• U-Factor. How fast heat escapes. Lower is better. For Utah's rebates, 0.22 or lower.
• Solar Heat Gain Coefficient. How much of the sun's heat gets through. Low numbers block it and high numbers let it in. ENERGY STAR's Northern zone sets a floor of 0.17.
• Visible Transmittance. How much daylight comes through. Higher is brighter.
• Air Leakage. How much air gets through the window itself. ENERGY STAR windows show 0.3 or lower.
• Condensation Resistance. Higher numbers resist condensation better, which matters on a cold January morning.

Keep the stickers. ThermWise asks for the NFRC sticker from each window with the rebate paperwork, along with the dimensions of every window.

What it means for your rebate

On a qualifying home, Wattsmart pays up to $50 per window, and ThermWise pays $2.50 per square foot of window on gas-heated homes. Only windows at 0.22 or lower count for either one, and new construction does not qualify for either one.

Rebate approval is made by the utility. The full conditions, deadlines, and a dated change log are on the rebates page.