Wood heaters and fireplaces require an efficient flue system and simple physics will tell you that combustion requires oxygen.
So it is logical that the air consumed by combustion needs to be replaced.

Ambient air (external) will be required to replace that which is consumed by the combustion process.
Ambient air is air outside the dwelling and it needs to enter the room the fireplace is in.

The Condor Draftmaster system is designed to allow ambient air into the room on demand.
The air is preheated via the flue system prior to entering the room replenishing oxygen the fire has consumed.

The entire system is fabricated in stainless steel and is supplied with custom roof flashing fabricated to suit roof pitch.
The flashing also provides structural strength to the installation

The Condor system has a manually adjustable ceiling vent, designed to control air ingress, incorporated in the system.
This can be closed at any time but usually at end of season.

History

The concern for replacing the air was not as wide spread as it is today.
Houses of the past were not sealed as well as the build of today and therefore did not have the issue of negative internal pressure caused by combustion.

Added to that most homes has external wall venting which allowed air to enter on demand.