It’s so hot, many people won’t venture out of their air-conditioned homes, even for ice cream.

The thermometer inched above 100 at the Dairy Queen in Antioch on Sunday, which you would think would be a good thing if you happen to be in the business of selling New York Cheesecake Blizzards in Antioch.

But even in the ice cream racket, it turns out that there is such thing as too much hot air, according to Dennis Kim, who manages the DQ on East 18th Street.

“It’s not too busy,” Kim said at about 4 p.m. “I like the temperature between 85 and 95. When it is over 100, people stay home.”

All over the Bay Area Sunday, folks were adjusting to unusually hot weather, which ranged from the 100s inland to the low 70s along the San Francisco coast. In San Francisco, that meant leaving the sweater at home. In Oakland, that meant an emergency trip to the

hardware store.

“How many fans walked out the door today? I’d say at least 20,” said Mario Chavez, a salesman at Markus Supply Ace Hardware, at 625 Third St. in Oakland. “I got a few left, not many, but more coming tomorrow. The heat is just starting. It’s going to be hot for a while, boss.”

By 10 a.m. Sunday, the temperatures hovered around 80 degrees in San Francisco — about 20 degrees above average for a morning in June. Temperatures kept rising in the Bay Area throughout the day. Record highs of 97 were recorded at airports in both San Francisco and Oakland, while Livermore and San Jose also smashed previous milestones. San Jose hit 103 and Livermore 106.

“This whole heat event will be the most substantial heat wave we’ve had this season,” said Charles Bell, a meteorologist for the National Weather Service in Monterey.

San Francisco hit 88 degrees Sunday, beating the record set in 1993 for June 18, but Bell said the existing record for the day “is not really that high.” Saturday’s historic high is 95, while Monday’s is 92.

Breaking any records Monday is “very unlikely,” Bell said. “Sunday’s heat is probably the peak for the entire event,” although the heat wave is expected to last well into the week. By Friday, Bell said the high pressure system lingering overhead will move toward the east, allowing cooler weather to work its way back in.

“It’s not an unprecedented heat wave,” Bell said. “We typically will have several periods every year where we’ll get very warm to hot weather . ... Usually we’ll get this two to three times a year.”

But just because it’s happened before doesn’t mean the weather-weary Bay Area residents are prepared.

“Be careful about leaving children and pets in cars, and please be aware that the vehicle will heat up to a dangerous level very fast,” he said. “Take plenty of breaks, and drink water.”

There were cases and cases of cold water Sunday afternoon at the Gene Friend Rec Center in San Francisco’s South of Market neighborhood, where about 100 congregants from the City Life Church on Sixth Street gathered to eat chicken and ribs after the 11:30 service.

“Just kicking it with the family on Father’s Day,” said the Rev. Marquez Gray. “We brought in extra tents because of the heat — most people are sitting in the shade. But it’s not bad — San Francisco has a nice cool breeze, unlike the East Bay.”

Around the corner on Sixth Street, where there are a lot more places to buy cold beer than ice cream, double-scoop bowls of Mitchell’s Grasshopper Pie were in high demand at Icu Market Deli. “We are the only place on Sixth Street with Mitchell’s ice cream,” said manager Willie Jay. “There are places in the mall with ice cream, but they don’t got Mitchell’s. We’ve been getting groups coming in all day — a lot of couples.”

A Spare the Air alert was in effect for the Bay Area on Sunday as the combination of high temperatures and traffic exhaust threatened to create unhealthy air quality. The California Department of Forestry and Fire Protection also issued a red flag warning for the Central Sacramento Valley, which means the area’s hot and dry conditions made it vulnerable to wildfires.

The heat, and the increased reliance on air conditioning that came with it, also taxed the Bay Area’s power grid. As of 8:30 p.m., more than 43,000 PG&E customers were without power, including 18,131 in the East Bay and 13,551 in the South Bay.

Trisha Thadani and J.K. Dineen are San Francisco Chronicle staff writers. Email: tthadani@ sfchronicle.com, jkdineen@ sfchroncile.com Twitter: @TrishaThadani, @sfjkdineen