Direct air is becoming increasingly important when installing a stove in a relatively new house. This is due to the fact that new builds are virtually air tight and very little heat and therefore air is allowed to escape.
Direct air will allow the stoves main combustion air to be taken from outside the building. This makes the stove more efficient and safer because it is not using the warm air it has just created or the air that the rooms occupants will need to breath.
A typical stove consumes between 14 to 25 cubic meters of combustion air every hour and a typical UK living room has an approximate volume of air around 40 to 50 cubic meters, so a stove operating in a modern draught-proof room could quickly present problems. In a new dwelling an external air supply to the stove ensures that there is an unlimited flow of combustion air which will help with the effectiveness of the flue up-draught thus also helping to avoid the potential escape of dangerous emission such as carbon monoxide.