Westborough Public Library patrons' use of the building will change for the fall starting Sept. 19.

But, they'll feel more comfortable in the building starting around Dec. 4.

The heating, ventilation and air conditioning replacement project will result in the building's meeting room, often used by tutors, closing Sept. 13.

Some book stacks may be unavailable at times, too, says Karen Fay, vice chaiman of the Westborough Public Library Board of Trustees.

However, a roughly 30-year-old system will go out the window when the project ends, she says.

"It's about to die at any second. It actually did die at one point," being "out for a couple of hours during the summer," Fay says.

"It's a couple of months past where we wanted it to be."

Crews will work from 7 a.m. to 3:30 p.m. weekdays, and some weekends, Fay says.

Most of the demolition will occur from 7 to 10 a.m., she says.

Noise and air quality will be tested daily, Fay says.

Library officials will post news of unanticipated changes in hours or services on the library's website, and Facebook and Twitter feeds, she says.