Massachusetts fire officials are investigating what sparked a blaze at a townhouse in Brookline early Thursday morning.
The fire broke out at 2:35 a.m. at 5 Carlton St. and quickly reached 3-alarms.
Crews were able to knock the fire down at the two-unit townhouse and residents of both homes were able to escape safely.
The exact cause of the fire remains under investigation but authorities think it may have been caused by a faulty heating unit in the basement of one of the homes.
Fire officials said damage to the building is estimated at $1 million.
