Energy-efficiency updates don’t come close to saving homeowners their promised energy savings, according to a surprising new university study. The study, not yet peer reviewed, is questioned by the federal Energy Department, which plans to release its own study soon.

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NEW YORK — Home-efficiency measures such as installing new windows or replacing insulation deliver such a small fraction of their promised energy savings that they may not save any money over the long run, according to the surprising conclusion of a University of Chicago study.

The study, which used data from a random sample of 30,000 low-income Michigan households that were eligible for an Energy Department home-weatherization program, found that the projected energy savings were 2.5 times greater than actual savings. As a result, energy bills didn’t decline nearly enough to eventually pay for the initial cost of the upgrades.

“The problem is that the real world is screwy,” said Michael Greenstone, an energy economist and head of the Energy Policy Institute at the University of Chicago. “The models project much larger savings than are realized by homeowners.”

The study, conducted by Greenstone and University of California at Berkeley economists Meredith Fowlie and Catherine Wolfram, has not yet been reviewed by a panel of peers.

But Greenstone says he is finding similar results in a second study of middle-income homes in Wisconsin. If his findings are correct, they could undermine the rationale for billion-dollar federal and state efficiency programs and call into question a long-held understanding that making existing homes and businesses more energy-efficient is among the cheapest ways to reduce emissions of carbon dioxide.

States are expected to expand efficiency programs like the federal weatherization program in the coming years to meet regulations now in development at the Environmental Protection Agency to reduce emissions from power generation.

“It’s urgent we find out which (programs) reduce carbon emissions at least cost,” Greenstone said.

The researchers found that while homeowners saw their energy use fall by 10 percent to 20 percent after the upgrades, that put them in position to save just $2,400 in energy expenses, far less than the average $5,000 the upgrades in the study cost. The researchers calculated that it cost the federal program $329 for every ton of carbon dioxide it saved. The government estimates the cost to society of a ton of carbon dioxide is $38.

The Energy Department said in a statement that the program, which it says has upgraded more than 7 million homes and is saving families $300 million a year, has been shown to work by previous national studies. Oak Ridge National Laboratory is set to release its own study on the program this summer that “should show that families are still saving more money in energy bills than money spent updating their homes,” according to Energy Department spokesman Eben Burnham-Snyder.