Officials yesterday investigate the deaths of three people at 345 Blackstone St., Providence, on Monday.

The Providence Journal / Kris Craig

PROVIDENCE — Carbon monoxide poisoning killed a family of three who were found dead in their South Providence house, Dr. Thomas Gilson, the Rhode Island chief state medical examiner, ruled yesterday.

No foul play is suspected, he said.

The police and Rhode Island State Fire Marshal Frank Sylvester said carbon monoxide accumulated in the family’s house, at 345 Blackstone St., because a basement furnace for the heating system was improperly installed shortly before New Year’s Eve.

No licensed plumber could have done the installation “because it is so wrong,” said police Maj. Stephen Campbell. For the time being, however, the police have refused to divulge how the installation was flawed or to answer certain other specific questions about the heating system.

Carbon monoxide forms as a lethal gas when a carbon fuel burns with insufficient air. It can leak out and build up dangerously when it is not properly vented, and because it is odorless, tasteless and invisible, it can collect unnoticed as a family sleeps.

The police found the bodies Monday, after a relative raised an alarm. While the victims’ identities have not been officially determined by the medical examiner, a neighbor and a friend have said that Sonia M. Flores, 46, also known as Sonia M. Aleman; her 14-year-old son, Ryan Aleman; and Flores’ boyfriend lived in the house.

Ryan was a ninth-grader at the Shepard campus of the Met School downtown. Acting on the assumption that he died, Mayor David N. Cicilline and Police Chief Dean M. Esserman yesterday morning commiserated with Ryan’s grieving classmates and teachers at the school.

“It was very sad,” Esserman said.

The deaths were discovered after a grown-up son of Flores who is serving in the Navy called a neighbor and said he could not get in touch with the family. He asked the neighbor to check on them, and after the neighbor got no response, the police were summoned. Officers entered the house at midday Monday and found the victims.

Ryan lay dead in a first-floor bathroom, his mother in a second-floor bedroom and the boyfriend in a second-floor bathroom, according to the police.

Due to the condition of the bodies, the medical examiner must rely on dental records to make a positive identification, Campbell said. Neither the medical examiner nor the police have said when they died.

The carcass of a pet rabbit, which had been caged in the basement, also was removed from the house. A private veterinarian was contracted to do a necropsy of the rabbit to determine its cause of death, Campbell said.

Officials yesterday continued to examine the heating system of the single-family house — the police said it is a forced hot-water baseboard system with a gas-fired furnace — and to analyze the air inside. There is no chimney on the roof of the house but a metal furnace vent pipe protrudes from the side.

The house was sealed overnight Monday through early yesterday and the system was left running in order to test the carbon monoxide level, according to Campbell.

Representatives of the gas utility company, National Grid, and city plumbing and mechanical-systems inspectors returned to the house yesterday. They were joined by an unnamed consultant who has been retained by the city.

The gas service to the house was disconnected yesterday, as firefighters stood by as a precaution, and the police said they plan to have the furnace removed today.

Sylvester, whose office is assisting with the investigation of the accident, came to the scene yesterday afternoon. He told news reporters that the furnace that was recently installed was new, but the police pointedly have declined to say that. He said he does not know who did the installation.

The house had smoke detectors but not carbon monoxide detectors, according to Sylvester. The state Department of Health and Sylvester advised Rhode Islanders to install carbon monoxide detectors in their homes and garages.

“You can’t see it. You can’t smell it. You can’t taste it,” Sylvester said of carbon monoxide. It is as important, if not more important, for a household to have carbon monoxide detectors as smoke detectors, he added, because smoke, at least, is visible.

If anyone suspects a carbon monoxide problem, contact the local fire department, the Health Department said in a statement. The department recommended a Web site for more information about carbon monoxide poisoning: http://www.health.ri.gov/topics/carbonmonoxide.php.

gsmith@projo.com