How dangerous are freon fumes for my kitten and guinea pig?

The condo I just moved into doesn't have air conditioning, but the landlady left an air conditioning unit to use during the summer. She said she just stuck it in the fireplace and it vented up the chimney and worked really well for her. I know that guinea pigs are sensitive to fumes; I also have an eight-week-old kitten who was a runt and malnourished the first week of life, so I want to make sure they both stay safe. Does anyone know anything about the effects of freon on pets, or whether it would vent correctly up the chimney and not into the room? I couldn't find anything online. To add to the difficulty, the guinea pig cage is about three feet away from the fireplace.