I understand it is safer and more efficient. Just for knowledge reasons I am asking. We converted to natural gas and lined the chimney. The old boiler had about 3 feet of vent pipe. It went up 2 feet and elbowed 1 foot into the brick chimney that went up the center of the house. When we first moved in I installed CO/smoke alarms in every room that the chimney traveled through just in case of cracks or leaks in the chimney walls. When we converted I was told natural gas must be piped up the chimney. I'm curious is co from natural gas different from co from oil? isn't carbon monoxide the same either way? :confused: Would have every one in the house slept "very well" if you know what I mean if we had vented the new boiler the same as the old?