The alarm at the 6-story building alerted hazmat crews to the scene.
More than 130 people were evacuated from the 57-unit apartment building.
There were no reports of any injuries.
Many residents were ushered onto warming buses while hazmat crews shut off the heat and worked to ventilate the building.
The American Red Cross was on hand to provide food and water to displaced residents.
A Fire Media Affairs spokesman said carbon monoxide readings were over 200 parts per million when firefighters arrived on the scene.
Investigators say a faulty furnace may be to blame for the high levels of carbon monoxide.
