Novato fire officials say five people -- including a mother, two teenage girls, an infant and another person -- showed up at Novato Community Hospital around 7 a.m. Thursday complaining of nausea, headache, trouble breathing and vomiting.
The five were transported to a Walnut Creek hospital, where they were treated in an hyperbaric chamber.
After the incident, the Novato Fire Protection District sent firefighters to check the family's home.
A fire district spokesman says firefighters measured the carbon monoxide levels in the home at 417 parts per million -- an amount that can be fatal in three to four hours.
Firefighters found a wall heater wasn't ventilating out of the house properly.
