why does an outside air intake make a furnace more efficient?

Question

why does an outside air intake make a furnace more efficient?

In: 2

Answer 1

Fire needs oxygen which is part of the air around us to burn. If you provied the air from inside a room, there might

a) be less oxygen in the air due to humans and animals using it up and

b) the airflow towards the fire is slowed down due to the minimally lower pressure that begins to form when the fire in the burner uses the air to get the oxygen and then pushes the smoke out of the chimney.

When you provide the air from outside the building, the air flows more easily and thus doesn’t slow down. It makes it easier for the fire to “breathe”.