Adding up

A slew of heated races and millions of dollars of out-of-state campaign contributions are fueling an unprecedented barrage of political ads. The 11 p.m. newscast of WCVB (Channel 5) on Thursday, for example, featured 16 political spots.

Daytime slots are just as popular: WCVB received 60 requests from political campaigns this week for the 35 available local ad spots on the syndicated talk show “The View.’’

“We try to avoid putting people running for the same office in the same commercial break,’’ said Andy Hoffman, Channel 5’s general sales manager, who oversees the scheduling of the ads. “In effect, it becomes impossible. There are not enough commercial breaks and too many advertisers. It’s been absolutely crazy.’’

The overdose of political ads is reminiscent of January’s special Senate race between Republican Scott Brown and Democrat Martha Coakley, but there are more this time because there are many close races and contentious ballot issues.

Bruce Mittman, president of advertising and marketing agency Mittcom in Newton, estimates that about $25 million has been spent on political ads in the Boston TV market since the summer.

“This is like hitting the lottery if you are on TV,’’ said Mittman, who is a partner in Community Broadcasters, which owns eight radio stations in New York State.

But what is a boon to the bottom line of TV stations can be a headache for their sales managers.

They are cramming so many political ads into their day and evening newscasts that they have to turn away regular advertisers and offer to run their ads on a station’s website or after the elections are over.

“Imagine the Southeast Expressway in a nasty snowstorm at 8 a.m., that’s what it’s like to buy [political ad] time now,’’ said Tobe Berkovitz, a political advertising professor at Boston University. “It gets to the point where you call up a station and say, ‘What have you got left.’ The inventory has been gobbled up.’’

Under federal guidelines for broadcast political ads, stations must sell ads to candidates at a rate lower than a typical advertiser pays. But the cost per spot depends on the station, the time of day, and the program during which the ad will air.

TV stations also can charge outside groups such as special interest groups a higher rate than candidates. In Boston, a 30-second spot on a popular prime-time network show such as Fox’s “Glee’’ or CBS’s “Criminal Minds’’ can cost as much as $25,000 for a political ad, according to two TV and advertising industry executives.

Most TV stations rely on an automated “traffic’’ software program, which handles the placement of ads. Sales representatives input the ads the station has sold. Depending on the demographic that the advertiser desires to reach and the availability of the time slot, the computer assigns a random rotation for the ads into a morning program, newscast, or network show.

A traffic manager or the general sales manager at the station makes sure that the schedule meets the client’s expectations, such as running frequently and not too close to other ads with similar products. But with so many political ads, these traffic managers are monitoring the rotation of the ads more closely to make sure that the candidates are getting fair treatment. For example, if the computer program assigns several spots by the same candidate back-to-back, the traffic manager or sales manager steps in to adjust the order.

But that has also been a challenge. “Sometimes they buy so much that you have only so much room,’’ said Chris Wayland, general manager and vice president of WHDH-TV (Channel 7), which sold out of ad inventory last week. “You can’t separate them because there is nowhere else to run them. You run into situations where every single break is a political ad and there is nothing you can do about that.’’

WFXT-TV (Channel 25) sales staff are also having to make room for the political ads over their regular clients. A spokeswoman for WBZ-TV (Channel 4) declined to comment on the station’s political ad spending.

At WCVB, Hoffman has been performing a delicate balancing act of managing local advertisers’ needs and those of the political candidates. When there is more demand than supply, Hoffman said, federal guidelines provide a pecking order to help facilitate the process. Top priority goes to federal candidates, followed by Massachusetts gubernatorial candidates, state candidates for offices such as treasurer, attorney general, and secretary of state, New Hampshire candidates, and issues.

“Every regular advertiser we deal with has had their schedule disrupted,’’ Hoffman said. “We are trying to squeeze everyone in and treating everyone fairly.’’

Johnny Diaz can be reached at jodiaz@globe.com.