A small fire in the commercial building at 55 Post Road West was quickly extinguished Tuesday night before causing serious damage.
Firefighters were alerted to the fire just before 9 p.m. Tuesday when employees reported a burning odor had been detected in the structure.
Three engine companies with a total crew of six firefighters and one officer were dispatched to the scene.
At the building, two employees told firefighters they smelled something burning in a rear stairwell.
Firefighters discovered a small fire burning in a first-floor bathroom, which was doused. Smoke was then ventilated from the building using fans.
The cause of the fire, which was investigated by the Fire Marshal's Office, was a door that ignited while it was propped open against a wall-mounted heater.
All fire units cleared the scene shortly after 10 p.m.