The State of Tennessee Chattanooga State Office Building is located in downtown Chattanooga on McCallie Avenue.

The polar cold enveloping the Tennessee Valley is taking its toll on people and structures.

Workers on the fourth floor of the State Office Building on McCallie Avenue say they reported to work Wednesday to a chilly 48-degree workplace.

Pupils at Thrasher Elementary were invited to bring blankets to school Thursday because a broken boiler was letting the biting cold creep into some classrooms and other parts of the building.

Heating units across the valley are failing -- or just unable to keep up with extremely low temperatures -- and the Tennessee Valley Authority is urging residents to dial back the thermostats until at least this afternoon.

WRCB meteorologist Paul Barys says temperatures this morning will hover around 10 degrees, and will likely feel colder because of wind chill.

"Probably some cold spots will get down to 0 [degrees], so you are looking at single digits in some areas," Barys said.

Today's warmest will still top out below freezing, at 29 degrees. Lows of 17 and 19 are expected for Saturday and Sunday, while highs for the two days will be 44 and 48 degrees, respectively.

TVA is asking residents across its seven-state region to dial the thermostat back a few ticks. Extreme cold stresses the power system, and the utility hopes to avoid power failures.

"When it's below 20 degrees, each time the temperature drops one degree another 400 megawatts of electricity is needed. That's almost as much as one of our larger hydroelectric dams," said Tim Ponseti, vice president of transmission operations and power supply. "Setting your thermostat two to three degrees below normal [overnight Thursday] and Friday morning can really help TVA manage the high power demand during this challenging time."

John Pless, spokesman for the Electric Power Board, said 68 degrees is a good conservative temperature setting, and residents may want to lower their thermostats by eight degrees when they leave the house.

In homes and businesses, prolonged cold weather can wear out heating systems, because units run constantly to keep buildings warm, according to Clayton Cornell, president of Reliable Heating & Air Co.

"But most of the time, it's people's perception. Most of the units in the Tennessee Valley are rated [to heat a home] when it's 20 degrees or warmer," Cornell said. "Even a perfectly functioning unit in 5-degree weather won't keep a home at the 72 degrees the resident may want. Nothing's wrong with it. It just can't keep up."

That might have been the issue at the State Office Building.

An employee said Wednesday she reported to work at 8 a.m. and the thermostat read 48 degrees on the fourth floor. By 9 a.m. that was up to 60, and the temperature rose steadily throughout the day. Meanwhile, employees in other parts of the building said it was cozy.

Kelly Smith, spokeswoman for the state's general services department, said Thursday in an email that keeping the climate steady in the aged building has been an issue. But by late afternoon the "conditions were comfortable" on all floors. The department's engineering manager will inspect the heating and cooling system today, she said.

At Thrasher Elementary, cold air was blowing from vents in some rooms Wednesday, according to Gary Waters, who manages facilities for the school system. But the boiler problem was repaired by Thursday morning, he said.

Principal Regina Brock said she doesn't know who suggested students should bring blankets, but it wasn't a schoolwide directive.

"We've been warm and toasty today," she said Thursday.

Contact staff writer Louie Brogdon at lbrogdon@timesfreepress.com or at 423-757-6481.