East Hampton Town Chief Fire Marshal David (Buzzy) Browne said work was being done at the 12 Huntting Road house when a blaze erupted there on the morning of Sept. 25.
The heater was affixed to the basement ceiling with a 3-by-4 feet metal grate on the floor, Browne said.
A tarp that had been placed down on the floor completely covered the floor grate. "Being as old as it was there was some considerable rust in the exhaust area," Browne said.
The thermostat was set very low, as the insulation was stripped from the walls, Browne said, adding that temperatures dropped to 50 degrees that night. "With the grate cover it pushed all the heat down and out to the exhaust, pushing flame out around the edges, igniting the wood framing of the floor," he said.
"Once the framing burned enough the heater dropped down onto the basement floor, leaving a large hole in the first floor," Browne said.
The East Hampton Fire Department, which was called at 8:19 a.m., made a quick stop on the fire. Browne said it can be repaired.
No one was in the house at the time of fire. No injuries were reported.