The fire in a downstairs storage room at 10 Meyer Road spread to adjoining drapes and other combustible materials, Fire Chief Christopher Gray said.
The homeowner smelled smoke and called the fire department but was able to extinguish fire with water at about 5:50 a.m. before firefighters arrived, Gray said.
"A few more minutes and it would have been a different story," Gray said.
The room sustained moderate smoke damage, and flames damaged one of the three aquariums in storage, with the total damage estimated at $1,000, Gray said.
No injuries to firefighters or the home's residents were reported.
Gray said that the house was difficult to access because it is situated well below the roadway and that a San Rafael police officer was on the scene before firefighters arrived.
Gray reminded residents to turn off heating units when they are not used under recommended conditions.
