When I was working in cabin insurance years ago, I spoke to an elderly client who was worried about carbon monoxide dangers in their home.  They had recently moved to a new state & had to rent a cheaper & older cabin for a year while their custom cabin was being built nearby. Although the older cabin is in unbelievably good shape considering it’s 70-year age, the oil furnace inside is questionable.  At the time, both of us were heading into late Autumn/early Winter weather & my client was worried about dangers of carbon monoxide fumes & whether or not they could disfigure anything in the home, which would prompt them to update their renter’s insurance. On the hand I was able to reassure the man that potential carbon monoxide fumes would not disfigure his belongings, since it is a light & smelless gas & is essentially benign to non-residing organisms.  But, I unfortunately had to warn the man that his life was what was genuinely in danger. All gas burning appliances—be it a oil furnace, an oven & range, or even a water heater—produce drastically small amounts of carbon monoxide when running respectfully. With oil furnaces recognizably, if they get dirty over time & are not cleaned respectfully, cracks will slowly form in the heat exchange & will allow more carbon monoxide to seep into your indoor air. Since it is smelless, the only way you would suppose is detecting the early flu-like symptoms before exposure becomes fatal, or you install carbon monoxide detectors alongside your smoke detectors.  Thankfully, several newer oil furnaces have auto-shut off safety features that chop power to the plan if it detects leaks in the heat exchange. This reassured my client & encouraged him to invest in a new oil furnace & multiple carbon monoxide detectors to be safer.