Known as the silent killer, carbon monoxide has made its mark on the winter season in New Haven.

Fire Marshal Joseph Cappucci said that New Haven is seeing more carbon monoxide-related incidents this year. He attributed the increase to heavier use of furnaces in face of recent cold temperatures. The trend has prompted city officials to inspect housing codes in New Haven buildings more attentively.

“This winter, we are seeing an increase in carbon monoxide calls at the fire department,” Cappucci said. “What makes it tough [to prevent these occurrences] is the cold snap and the snow, so now the furnaces are working harder.”

Over the course of thelast few weeks, multiple cases of carbon monoxide-related events have displaced at least 28 New Haven families from their homes. A recent case at the apartment complexes in DeDiego Court., near Union Station, evacuated the all building units on Jan. 15, said Mary Coursey, the spokesperson for Northland Investment Corporation—the company that owns the apartment complexes. The New Haven Register reported that another occurrence in 534 Smith Ave. hospitalized nine residents on Dec. 19.

Erik Johnson, the executive director of the Livable City Initiative—a branch of the Office of Economic and Business Development — said that city officials are calling for a closer look at housing codes in New Haven buildings.

“We need to enforce the housing code and remove people from unsafe situations,” President of the Board of Aldermen Carl Goldfield told the News last week.

Current building regulation in New Haven requires carbon-monoxide detectors to be installed in multi-family homes, said Johnson, and that not having proper ventilation is a building code violation.

The city intends on fining Northland based on an investigation that found 212 boilers with improperly installed vents in DeDiego Ct., he said, which also contributed to high levels of carbon monoxide. Johnson said that the city has told Northland to find a permanent solution to its building code violations by Feb. 11.

Northland responded by asserting the company’s dedication to its clients.

“Throughout our period of ownership we have worked closely with the City and LCI staff on improving the quality of life at [DeDiego Court],” Coursey said in an e-mail on Jan. 27. “We have invested nearly $2 million to date in capital improvements and have vastly improved the community living standards left in place by the previous owners.”

Jessica Garcia, a resident at DeDiego Ct. who recently moved back home, said that she thinks Northland failed to provide enough explanation regarding the incident.

“They didn’t give us any answers,” she said. “Somebody from the other building got sick and the Fire Department [evacuated us]. I felt homeless.”

WTNH reported that all units were notified they could move back to their homes on Jan. 25.

But Coursey told the News on Jan. 27 that nine families still remain in area motels.

Caroline Kornegay, another resident, said that the level of carbon monoxide in her apartment reached 1000 parts per millions, a level that would usually require immediate attention.

A similar incident in Waterbury which sent 20 elementary school students on Jan. 4 was also due to a combination of improper air circulation and increased furnace use, said John Cross, the school inspector for Waterbury Public Schools.