Since high efficiency furnaces draw air directly from outside the furnace itself does not require a fresh air intake in order to replace inside air that otherwise would have been drawn from the room the furnace is located in.
Furnace air intake inside or outside.
There are two types of airflow furnaces a downdraft or downflow furnace and an updraft or upflow furnace.
To keep smoky air outside close the intake using the damper.
Most people do not clean around the furnaces so that is usually the main cause however if the area around the furnace and the unit itself is cleaned regularly or yearly this will not really be an issue.
The air passes through the filter of the unit and quickly passes over the supercooled coils inside.
Fresh air is brought in from an outside intake hood and dispensed in the return air duct.
The other air loop is through the ducts in the house.
On the other hand if you were using the inside volume of air in the house for combustion it would be pulling it into the furnace and sending it right outside.
Due to high efficiency furnaces having their own fresh air intake no air is drawn from inside your home.
Houses are not airtight though.
This return air intake grille typically includes some type of filter to keep dust and debris out while allowing air to pass through.
Typically a furnace will suck air from inside of the house probably the vent behind your couch pass it over the heat exchanger and blow the now hot air out of the vents in your rooms.
The furnace is now a closed loop system pulling air from the outside and then sending it back out with the combustion gases.
The flow of air.
Unfortunately the fresh air intake you have described is the second type and does not provide direct combustion air to the furnace room as it is directly connected to the return air plenum for.
It is easy to install a fresh air intake for a furnace.
This typically does not pull a significant amount of air from outside because that would waste a lot of by displacing heated air to outside.
Usually these small filtered vents help improve air quality since the air outside is typically fresher than the air outside.
It is then heated by the furnace and distributed through the home.
The issues with having the intake air being taken from inside the envelope of the structure is that normally the intakes will suck up a lot of dust from the basement.
High efficiency furnace combustion intake from inside or outside.
But during a wildfire they can pour unhealthy air into your home s interiors.
Typically the fresh air intake will be located in your attic or ducted to the return side of the home s central air handler.