Quite few years ago when my friends' parents divorced his father moved into a motel about five blocks from the house where they used to live, together. The motel had a gas in-wall heater on the interior wall between the main room and the bathroom, about a foot and a half from the bed.
It was the perfect little place for a bachelor. The maid would clean the tiny room while he was at work, restaurants and his former home were nearby, and he could cook on a hotplate or in the microwave he bought for the very few times he cooked anything in the 14 years he lived there.
The wall heater was never serviced in that entire time, and why would it be? On cold winter nights it kept the small room cozy and warm, and such heaters have been common around these parts for almost a century. My friends' fathers' last year at the hotel was particularly cold. He came "home" from work on a freezing night, -20 with the wind chill, cranked on the heater and promptly curled up in bed to go back to work the next morning.
That was his last night with us. It seems a mouse tried to make a nest in the stack of that wall heater. In a few hours the room, while cozy and warm, was also filled full of the exhaust gasses that you seem so smitten with, OP.
The man died in his sleep, unaware of his fate until it came for him.