My co detector is mounted about 1/2 way up the wall and about 5 feet from the stove per it's instructions. But it is designed for RV, not household use
But, it occasionally trips off if I am cooking and don't have enough ventilation. It's sorta a reminder to add ventilation if I forget.
For those that try to use the generally unsafe practice of cooking flower pots for heat, it will go off.....
As far as your
furnace, externally vented furnaces should not trip it off unless there is a CO leak and you will want to know about that. I can't comment on older panel type heaters.