At least 100 people were evacuated from the facility and an adjacent hospital.
Hollywood Police Chief Tomas Sanchez said the Rehabilitation Center at Hollywood Hills facility has been sealed off and police are conducting a criminal investigation.
Cristina Bichachi, the former business development director at the Rehabilitation Center at Hollywood Hills, told the Associated Press that the air conditioning went on the fritz "many, many times" during the three years she worked there.
Police have started a criminal investigation into the deaths.
Calls to the owner and other officials at the Hollywood home were not immediately returned, but the facility's administrator, Jorge Carballo, said in a statement that it was "cooperating fully with relevant authorities to investigate the circumstances that led to this unfortunate and tragic outcome".
High temperatures were forecast to reach the upper 80s Fahrenheit (low 30s Celsius) in Florida's two biggest cities, Jacksonville and Miami, and the mid-80s F in Atlanta over the next week or so, according to meteorologists at AccuWeather. "I don't know if she is dead or alive", Ms. Mitchell said.
Then there are those who die from carbon monoxide poisoning because they run generators in enclosed garages or inside their homes. The deputy was overcome by fumes while approaching the home and called for fire rescue.
A total of eight others died in Georgia and the Carolinas. Thousands of anxious residents who evacuated have been pressing to be allowed to return home.
"Most of the patients have been treated for respiratory distress, dehydration and heat-related issues", Randy Katz, a spokesman for Memorial Regional Hospital, told reporters.
Restoring power is still a top priority in Florida.
The number of deaths blamed on Irma in Florida climbed to 13 with the carbon monoxide deaths, in addition to four in SC and two in Georgia.
Irma earlier left a trail of destruction in the Caribbean, where almost 40 people were killed.
"We've got a lot of work to do, but everybody's going to come together", Florida Gov. Rick Scott said. Reacting to the number of casualties, Mr Trump said: "When you think of the incredible power of that storm, and while people unfortunately passed, it was such a small number". He and his wife, Deb, have been without power for six days. About 110,000 people remained in shelters across the state.