Fire Chief John McArdle said the family was given oxygen treatments on scene and later checked into Anna Jaques Hospital in Newburyport, Mass., where they received additional treatment.
Fire crews measured carbon monoxide levels in the house at 100 parts per million, McArdle said. Detectors usually sound at 35 parts per million. Levels become deadly at 400 parts per million.
The Fire Department often responds to carbon monoxide calls only to find batteries are low or the detector is broken.
"In this case, a potential tragedy was averted by a $25 or $35 detector," McArdle said.
McArdle returned to the house later in the afternoon to check levels again and asked the gas company to check the home's heating system.
Carbon monoxide, which is odorless, is created through the burning of fossil fuels. Exhaust from kerosene water heaters and oil furnaces are usually vented outside, but occasionally problems can arise, McArdle said.
He encouraged every homeowner to have fire and carbon monoxide detectors, which should be placed in or near bedrooms.
The family affected yesterday, whose name McArdle could not release, was conscious and OK.
Early symptoms of carbon monoxide poisoning include headaches and flu-like symptoms that can often be overlooked, he said.