As of this tax year, the acronym NFRC is suddenly relevant to John Q. Public.

That's because taxpayers who want to earn a $1,500 home-energy tax credit for replacement windows or energy-efficient exterior doors must choose only those products that the NFRC—the National Fenestration Rating Council—has tested and certified to meet the feds' high standards for energy efficiency.

Energy Star-rated products don't automatically qualify. Indeed, the U.S. Department of Energy advises that most Energy Star windows aren't efficient enough to earn the tax break for buyers. You need to check the particulars of the NFRC rankings, says DOE spokeswoman Christina Kielich.

For taxpayers to qualify for the big new tax credit, windows, doors and skylights need to have official scores of .30 or lower on two NFRC certification tests:

  • The U-Factor, a measurement of how well they keep heat indoors.
  • And the SHGC, short for Solar Heat Gain Coefficient, a measurement of how well they keep the sun's heat out (the better to minimize air-conditioning costs in the summer).

How can you tell which products qualify?

In theory, the answer is simple: Just look for the NFRC label. We've annotated a sample NFRC sticker here with notes on what the various numbers mean.

But labeling is voluntary and recent spot checks at hardware stores around the region revealed that the stickers weren't always affixed to the floor models. Then again, in one store where an NFRC label on a window clearly showed a disqualifying rating of .32, a clerk assured a Daily News reporter that the window was good for the tax credit.

Let the buyer be advised to observe the usual caveat emptor.

To help steer customers in the right direction, both Home Depot and Lowe's are using their own stickers to designate products that qualify for the tax credit. Home Depot takes things a step further, with software at the custom-order desk that's programmed to order only qualifying windows, provided you tell the sales staff that's what you're after.

Still, says Jen King, a spokeswoman for the chain, "It's really important for people to do the homework."

The most direct way to study up is to visit the manufacturer's Web site for an official "manufacturer certification statement" and a chart showing the exact makes and models that came in under .30 for U-Factor and SHGC.

The $1,500 tax credit is a big selling point right now— "It's definitely something that we've been seeing people come in and ask about," King says. So most manufacturers make the information easy to find online. Print out the chart and take it with you when you shop.

Print out a copy of that certification statement, too. You'll need it, along with your receipt, for tax documentation.