Do gas stoves or fireplaces require a chimney?

Some do and some don’t. There are essentially three kinds of gas stove or fireplace vent configurations. One is natural or “B” vent. This means the appliance requires a vertical (through the roof) vent termination. The second is referred to as “direct-vent”. This means the vent can terminate horizontally (on a side wall) or vertically. The third is referred to as “non-vented”. This means there is no chimney requirement. Non-vented are not certified in Canada.