Firefighters responded to a report of possible carbon monoxide poisoning at a home at 426 Carmel Ave. at about 7:30 a.m., fire authority spokesman Matt Lucett said.
Two adults and a child had evacuated their home complaining of nausea, headaches and an altered level of consciousness.
Firefighters treated the three victims at the scene and took them to a hospital for further evaluation, Lucett said. They were later released.
Firefighters took air samples in the home and reported finding moderate levels of carbon monoxide.
PG&E crews were called to the scene to investigate and determined the source of the leak to be a furnace that was emitting the odorless gas into the home, PG&E spokesman Joe Molica said.
The leak was fixed, and the family was allowed to return home. Molica said that PG&E offers free appliance screenings in order to detect possible leaks.
"We're happy to come out and ensure that a customer's appliances are working correctly," Molica said.
Appointments for free inspections can be made by calling (800) PGE-5000.
The utility company and fire authority also recommend that homeowners install carbon monoxide alarms to prevent accidental poisoning.