What can daily low level carbon monoxide poisoning do to you over time?

CO is no good: Cigarette smokers get a dose of co with every drag. Most cigarette related pathology is not due to co however. Higher levels as from faulty gas space heaters can cause nausea, visual disturbance, headache, cognitive dysfunction, aggravation of cardiovascular disease and, if long enough exposure even death.

Uncertain: We don't know the effects of low level co poisoning over time. It surprises many people to hear that smokers can have 10-12% of their blood saturated with carbon monoxide or even more in heavy smokers. Since it displaces oxygen from red blood cells, there are probably some long term consequences such as premature aging, but it hasn't been studied in a way that we can be certain.