The mercury hit 103 at Logan Airport, making it a tie for the hottest day since 1926.
And the Boston Fire Department had to fight a three-alarm fire in the heat.
The blaze, in a three-story duplex at 1953 Columbus Ave. in Egleston Square, sparked a traffic nightmare, but no residents were injured. A firefighter was taken to a hospital with chest pains, however.
The Boston Fire Department Tweets that the damage is estimated at $250,000. The Salvation Army is assisting those turned out of their homes by the blaze, according to the department.
The blaze was apparently caused by someone carelessly disposing of a cigarette on the third floor back porch, according to the Fire Department. Twelve residents were displaced.
In the accompanying video at above right, a fire official explained that because of the heat, firefighters worked in shifts of no more than 15 minutes. That drove some of the need to take the call to three alarms, he said.