https://www.cpsc.gov/Safety-Education/Safety-Education-Cente...
https://www.cpsc.gov/Safety-Education/Safety-Education-Cente...
(All time low 380ppm -- 10% above the world average during my birth :-( , highest 1620ppm)
[1]: https://www.abe.iastate.edu/extension-and-outreach/carbon-mo...
* The boiler's flame is visible (through a slit).
* The system doesn't have a separate supply stream -- it takes oxygen from the flat.
An CO sensor seems obligatory to me: after the chemney sweeper (obligatory in Germany) measured 10,000ppm CO in the exhaust stream (defect, not normal operation), I didn't want to depend on a 25y+ boiler's electronics alone.
CO kills relatively fast. Even if rare, I don't want to die caused by a rare event that could have been avoided by spending ~50€ (here)
We had one a new one that just beeps when high. Except it didn’t. Delayed medical treatment for months since it never went off.
Gas company guy showed us how high levels in house was and the alarm was silent. Even with fresh batteries.