If these heaters malfunctioned there would be a federal consumer protection safety alert, a freeze on the sale of the heaters, and lawsuits galore. Can't recall seeing a single issue EVER for millions of these heaters sold.
This model is tiny. Check out the dimensions.
IGNORE doom & gloom gossip. File it along with comets, asteroids, Nessie, Sasquatch, and "Honest Used Car Salesman".
Hundreds of people have used hundreds of CO detectors trying to get a alarm. Same for O2 shortage -- good luck. If you're worried and have 16 people on a sleepover crack a window. These heaters DO need a couple of feet clearance to the front and overhead.