The Sunday night two-alarm fire was ruled accidental, officials said on Thursday.
The fire was caused by a malfunctioning heater in the attic, Fire Chief Michael Roberts said. The cost of damage is still currently unknown.
The house fire on Browning Road in the Short Hills section of Millburn was quickly extinguished by firefighters with little visible damage to the home and no injuries.
Fire officials declined to speculate on the cause of the 5 p.m. blaze, which caused damage to roof of the single-family split-level home.
The fire was contained to the home and was extinguished by 6:30 p.m.
Firefighters remained at the scene accessing the damage but fire officials said they were recommending the family not stay in the home overnight.