Student here. I’m having a little trouble understanding this, please correct me!
As I understand things, connecting a fuel burning appliance to a masonry chimney was common when the appliances were around 60% efficient. Now that appliances are >80%, they need their own vent to the exterior of the building. This is because the combustion air can condense in the flue, potentially causing moisture problems (also containing toxic gases that may seep into the building).
Appliances that are 80% efficient, burning natural gas or propane must use a metal B-Vent.
Appliances that are 80% efficient, burning oil or gas, must use a metal L-Vent.
Appliances that are 90% efficient, must use a plastic PVC vent.
Appliances that use electricity as a “fuel” do not need venting to the exterior of the building.
Is this correct?