What is Type L vent?

What is Type L vent? Type L vents are designed for venting approved oil-fired and natural-gas appliances that produce draft hood flue gasses that do not exceed a temperature of 570º F (299º C), or 926º F (299º C) for 10 minutes in an over-fire situation. Type L vents should not be used to vent coal- or wood-fired appliances.

Where are L vents used? Type L Vents – Double Wall Metal Vents