Here's a little test for savvy home remodelers and students of the Realtor magazine/National Association of Realtors annual Cost vs. Value Report:

Of the 35 projects listed therein, which one came closest to 100 percent this year?

In other words, for which project would homeowners regain almost every dollar spent when they sold the house?

Not a major kitchen redo. Not the bathroom. Or the roof. (The Cost vs. Value ratio for that is only 56 percent.)

Not even windows, vinyl or wood, exceeded the 66 percent mark.

If you guessed, bravo: It's a steel entry door.

Replace an existing front door with a new steel door, and you will, the report says, recoup 83 percent of its cost.

If the door is made of fiberglass, the ratio is reduced to 61 percent.

The 2013 Cost vs. Value survey did not include wood doors. The probable reason, those interviewed said, is that wood doors are so much more expensive than fiberglass and steel. (The door businesses contacted for this article do not sell wood doors.)

The data, which are based on contractors' estimates, are compiled annually by Realtor magazine and the Realtors group, based on responses from a members survey. This is the first time in six years that the overall percentage has improved.

The Cost vs. Value Report has been around for at least 25 years, but it's only been since 2009-10 that exterior-door replacement projects have been included.

The reason?

Two words: Curb appeal.

"There was some interest [in curb appeal] in 1977," said Dave Radulski, the year he ventured into the door-selling business. "But it's not like it is now."

Radulski is sales manager for P.J. Fitzpatrick Inc., which has several locations in the Philadelphia region.

It's hard to say whether the current Cost vs. Value ratio will hold up over a long time, Radulski said. Thus far, no real trend has emerged.

In the 2009-10 report, for example, a steel-door replacement returned to a home seller in the Philadelphia area almost as much as was spent on it: 97.5 percent.

In 2010-11, the percentage was nearly the same, but the next year, it dropped to 67.1. And now it's back up again, to 83 percent.

The return on fiberglass doors, which are more expensive and better insulated, did not fluctuate as much.

But the question still hangs out there: Why steel?

Steel doors are utilitarian - not exactly your Sunday-best kind of material.

"It does surprise me," said John Matusik Jr., co-owner of B&M Custom Cabinetry in West Deptford.

Fiberglass looks good, he said, but steel is just a plain door: "It doesn't pop, it has no warm feeling."

Matusik said fiberglass is more valuable than steel; people upgrade to fiberglass, not the other way around.

"Steel is usually reserved for the side or the back. Maybe it's for security."

True, said Drew Miller, owner of Drew Miller Custom Builder in Collegeville. But a door, in general, tells a prospective buyer what the seller of the house is like, he said: They "knock, ring, look and judge."

Or, he said, they do virtual tours online. "They cross a property off without going to see it."

Homeowners who are ready to sell should inspect their door's weather stripping, secure the hardware, and clean up the threshold, Miller said. "Nobody likes leaky doors; it's a security issue to them."

Ron Lomonaco, an owner of Guida Door and Window in Philadelphia and Boothwyn, recounted this tale:

About six years ago, an elderly man came into the Boothwyn store. He told the staff he had lost his wife and needed to sell his house.

"He wanted to do something to have curb appeal," Lomonaco said. So the elderly man bought a door with sidelights, nice hardware, and expensive glass.

When he sold the house, Lomonaco said, the new door was not only an important reason, "but he got every penny back. . . . His idea worked."

Paul Bondy, president of Exit Realty in Ambler, said the reason the Cost vs. Value ratio is so high is that the front door says home:

"The homeowner makes it his. If you are not making that emotional connectivity, forget it."