It's been awhile since we've really had to fire up those home furnaces.
And after a long summer of not being used, those furnaces might not work so well when they're suddenly sprung into action.
Officials on the scene in Middleton Tuesday night say that's basically what happened at this duplex.
They say one woman was taken to the hospital and later transferred to Milwaukee after a problem with the chimney led to high carbon monoxide poisoning in her apartment.
"What we found is the chimney had collapsed on itself while they had worked on it some time ago," said Chief Aaron Harris, Middleton fire department, "Not allowing the gases to be properly ventilated from the home."
Officials say carbon monoxide poisoning can and does happen at any time of the year, but winter can be especially dangerous when homes are tightly closed up.
That's why the experts strongly suggest getting your heating systems checked out every year, before the cold weather hits.