Paramedics were called to a trailer in the Candle Lake area at around 9:40 a.m. CT on Saturday.
A 34-year-old man and a 32-year-old woman along with three children – including a 6-month-old baby – had varying signs of CO poisoning like vomiting, headache and lethargy.
The family was cared for by paramedics and then taken to Victoria Hospital in Prince Albert, Sask.
WATCH: The dangers of carbon monoxide
Parkland Ambulance officials said they had lit the furnace in the trailer for the first time this season and failed to remove the winter covers from the vents. Without proper ventilation, dangerous levels of CO built up.
Officials reminded people that every home or trailer should have a working smoke and CO detector.
Candle Lake is approximately 215 kilometres north of Saskatoon.