Two people were taken to the hospital after exposure to high levels of carbon monoxide in Northwest D.C., officials said.

About 7:50 a.m. Thursday, an ambulance was sent in response to a call about a sick person at a home at 921 Ingraham St. NW.

When firefighters arrived on the scene, they suspected that something wasn't right and called for a full carbon monoxide unit, said Ed Smith, president of the D.C. firefighters union. Initial carbon monoxide readings were high, D.C. Fire and EMS spokesman Battalion Chief Brian Lee said.

Two people were taken to the hospital in stable condition, Lee said, and others were treated at the scene.

The cause of the carbon monoxide issues was a malfunctioning furnace, Smith said.