Bill Payson of Lee isn't too worried about all this talk of a heat wave.

His house, built in 1774, always seems to stay pretty cool even without an air conditioner, so he has no plans to put one in before temperatures approach 100 degrees today and Thursday.

“If it gets too hot, I go down into the cellar,” he said. “There's always something to do down there.”

With temperatures expected to soar into the upper 90s and humidity levels on the rise, heat advisories are in effect for parts of central and southern New Hampshire until 7 p.m. today.

Forecasters said the combination of high heat and humidity could make it feel like 103 degrees.

“Everybody will want to go out to the beach, but I would avoid staying out there too long. Drink plenty of fluids and if you feel like you're getting too hot, seek the air conditioning,” said Stacie Hanes, a meteorologist with the National Weather Service in Gray, Maine.

The warmest temperatures of the year will arrive on the first day of summer and stick around until at least Thursday. Hanes said Friday's highs will reach the upper 80's to near 90, but temperatures will drop by the weekend through next week.

The heat comes at a time when most students have finished up classes for the summer. Summer break began for some schools last week, while others wrapped up early this week.

Tuesday was the last day for students in Raymond. This first summer heat wave wouldn't have been a problem for students still attending at Iber Holmes Gove Middle School because, unlike most, the school was built about six years ago and is fully air conditioned.

“It makes a big difference. We've been pretty fortunate when we've had a heat wave,” said Principal Ellen Small.

Companies that install and service air conditioners said they've been getting calls for tune-ups in recent weeks and they expect they'll increase once the heat arrives.

“Usually when it gets up to 90 degrees, everyone calls in at once. We had 50 calls in a day once,” said Alex Sherrill of Key Heating and Air Conditioning of Portsmouth.

Some people who haven't arranged for their air conditioner to be serviced may get a surprise.

“A lot of people are turning them on for the first time and they're finding out they don't work,” Sherrill said.

Air conditioners and fans are still available at area hardware stores. How long that remains the case remains to be seen.

“I'm sure they'll come in and try to wipe us out,” said Ryan Wheeler, a sales associate at Aubuchon Hardware in Nashua.

The Home Depot in Seabrook had plenty of fans and air conditioners in stock Tuesday, according to sales associate David Deschenes.

He said he's always surprised when he sees people showing up to buy air conditioners for the first time.

“I would think everybody in the world would have an air conditioner,” he said, “but there are people from the old school that don't particularly like air conditioners for the noise level.”

But newer air conditioners are much quieter than they were 10 years ago, Deschenes said.

Cheri Smith of Kensington hopes the heat breaks before her daughter's wedding, which will be held at her home Saturday.

She said family members from southern California were expected to arrive at the same time as the heat. They're used to heat, but not high humidity, she said.

Smith isn't the only one coping with the sticky weather. Jennifer Schultz of Epping said her husband plans to get the air conditioner installed before the heat hits.

“I hate it,” she said.

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Jason Schreiber may be reached at jschreiber@newstote.com.