Our family recently stayed at a newer home in Maine that used oil heat and hot water. The home had a constant odor of oil combustion, apparently due to heating the hot water, but the odor became very strong when the heat was turned on due to unseasonably cool weather.
I examined the heating system and observed a hole about ½ inch diameter in the exhaust vent, likely drilled out for a test probe, close to the burner. This was where the odor was coming from.
The owner insisted the open probe hole was not a cause for alarm, was common practice, and “helped the exhaust gases vent easier” through the exhaust piping.
I think he is mistaken, and Carbon Monoxide poisoning would be a risk.
I’d like to hear the experts weigh in.