In the US at least, high efficiency home gas furnaces bring in their own combustion air from the outside so they don’t bring drafts into the house. They also do

In the US at least, high efficiency home gas furnaces bring in their own combustion air from the outside so they don’t bring drafts into the house. They also don’t have flues throughly the roof. The exhaust gas is cool enough that it goes out wherever is convenient through a PVC pipe parallel to the intake pipes.