Calgary police say the man's death is not considered suspicious.
Carol Henke (HANK-ee) with the Calgary fire department says a concerned person called for help after hearing a vehicle running for quite awhile.
She says the colourless, odourless gas had leaked into three attached townhomes.
Nine people in those units were assessed and seven were taken to area hospitals.
Adam Loria with Calgary's Emergency Medical Services says the seven people, including four young children, were not in life-threatening condition.
Henke says firefighters who responded to the call did not hear any working carbon monoxide alarms in the neighbouring townhomes.
"It's a reminder to everyone, especially when you live in attached units, you can't control what your neighbours do," she said.
"For the safety of everyone's family, it's really important to have those working alarms."
— With files from CFFR