The appeal is obvious. With new football stadiums costing more than the annual economic output of small island nations, why don’t cities just fix up their old ones for a fraction of the cost?

That’s a bad idea for San Diego, according to the head of the mayor’s stadium task force, the Chargers and Qualcomm Stadium’s manager. The sum total of their opinions make it clear: Renovating Qualcomm isn’t going to happen.

“We don’t really believe it’s feasible,” task force chairman Adam Day said.

There are lots of different reasons why a renovation won’t work here, they all say:

• Qualcomm wasn’t built just for football. When it opened in the late 1960s, the stadium housed both the Padres and Chargers so views for fans aren’t maximized for football. That affects seating and what the team could charge for the best tickets in the house. “The design is dated,” said stadium manager Mike McSweeney. “In order to come in and renovate it, you’d basically have to take it to the ground.”

This is the same reason that most recent stadium renovation can’t serve as a model for San Diego. Five years ago, Kansas City renovated the Chiefs stadium for $375 million instead of spending $1 billion-plus on a new stadium. “The cost issue dictated the answer,” said Jim Rowland, who manages the Kansas City stadium. But Kansas City’s stadium was originally built only for football, meaning it didn’t have the view issues that Qualcomm does. The city was able to keep the stadium’s bowl and just build a new structure around it, Rowland said.

• The stadium is broken. Qualcomm needs about $80 million in repairs, including new plumbing, wiring and a scoreboard. There are also problems that have built up over the years that would be hard to fix. Workers who upgraded the soda machines in the stadium years ago didn’t entirely rip out the previous system, McSweeney said. On really hot days, syrup from the old tubes will leak out the walls and onto the floor, he said. “We can’t see in the cement,” he said.

• Past renovations didn’t work. A previous renovation in 1997 left the stadium with two different foundations that would make earthquake-proofing difficult, Day said. Beyond that, the 1997 renovation led to a money-losing contract with the Chargers and calls for a brand-new stadium just a few years later.

Still, these renovation hurdles have been known for a while. And they haven’t kept stadium watchers from talking about doing it, even people who are friendly to the Chargers.

Less than three years ago, developer and U-T San Diego owner Doug Manchester, the boosteriest of Chargers boosters, said he could fix the stadium for $200 million. In 2009, NFL Commissioner Roger Goodell floated a Qualcomm renovation as well.

For more than a decade, though, the Chargers have smacked down the idea. The last time the city had a stadium task force, the team’s architects said a renovation wouldn’t be much cheaper than a new stadium.

“The only serious studies of renovation that have been done for Qualcomm have concluded that renovation doesn’t make sense for a long list of reasons,” said Mark Fabiani, the Chargers stadium point man.

The local branch of the American Institute of Architects recently came to that answer, even though architects initially thought otherwise. But it wasn’t all for the reasons you might think.

Last month, Daniel Stewart, the local chapter’s vice president, penned an op-ed arguing for a renovation.

“With some imagination and focused design effort, San Diego can capitalize on these great bones and transform it into a state-of-the-art football venue,” Stewart wrote.

After the op-ed published, Stewart and an architect colleague of his, Jack Carpenter, met with Doug Barnhardt, who owns a construction company and is a member of the task force. Barnhardt explained some the site’s renovation difficulties – facts that gave the architect group pause. Carpenter left the meeting convinced that a renovation wasn’t going to happen. He still believes that it’s physically possible, but opposition from the Chargers and the task force meant the idea was dead.

“The politics are going to upstage the economics,” Carpenter said.

But Day, the task force chairman, believes the economics make his case. Day told me that his group has done some rough calculations on the cost of a renovation. He figures it would cost $100 million to fix the stuff that’s broken, $150 million to $300 million for earthquake-proofing and another $200 million to $300 million to give the stadium all the modern restaurants, wide concourses, restrooms and other upgrades the team wants.

“Why would you spend $700 (million) when you can spend a few hundred million more and get a brand new facility?” Day said.

I reminded Day of the task force’s recent presentation to a City Council committee, which listed a new stadium price tag as between $700 million and $1.5 billion. Isn’t a $700 million renovation a lot less than $1.5 billion new stadium?

Day said he expects a new stadium will end up in the middle of the cost estimate. Think $1 billion or so.

“I don’t think there’s anyone in our committee thinking you need to spend $1.5 billion to get everything you need for a stadium here,” he said.

Still, a roughly $400 million gap between the cost of a renovation and a new stadium isn’t nothing. Back in 2003, when the Chargers pitched a new stadium as part of a redevelopment of the Qualcomm site, the price tag for the whole thing was $400 million.