HOLLYWOOD (CBSMiami) – It was a close call for two families that live in a Hollywood duplex on Monday morning.

Hollywood Fire Rescue said they received a call from a person at 1925 Thomas Street who said they were not feeling well. When firefighters arrived, they found very high, lethal levels, of carbon monoxide when they entered the residence.

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“The numbers were extreme, they’re high,” said Hollywood Fire Rescue Division Chief Joel Medina.

So high that the seven people inside, including three children, were taken to the hospital as a precaution.

“Basically I heard the engines rolled up as far as the fire department and when I looked outside there were a lot of engine lights and everything,” said neighbor Stacy Williams. “Worried scared, concerned out of my sleep, so definitely I wanted to know what was going on.”

Investigators say the cause was a tankless gas water heater. The device, which was installed without a permit, was being used in a bathroom which is considered a dangerous location.

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“In speaking to the Teco Gas Company they advise that usually tankless water heaters are usually installed outside of the structure or in the garage or vented to the outside,” said Medina.

While inside the home, and clearing it for safety, investigators reportedly found a small amount of marijuana.

Monday wasn’t the first time Hollywood Fire Rescue was called to this home. They were called to the residence three times in the last three days, transporting somebody for each call. Investigators couldn’t say whether they were here for carbon monoxide.

“Carbon monoxide is definitely a lethal gas that can be detected. At this point in time we didn’t have any fatalities and everybody seems to be okay, they’re all being checked out,” said Medina.

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Teco Gas turned off the gas for the home and it was deemed safe for the families to return.