Advantages

Combustion heated homes benefit from drawing combustion air directly from the outside using sealed and insulated ductwork.

The advantages of this are:

1) Conservation of warm indoor room air.

2) Reduced infiltration of cold outside air through cracks in windows, doors etc...  When combustion air is drawn from a heated basement room, it returns to the outside through a chimney after combustion in the firebox. This loss of air depressurizes the interior of the building, with pressure recovery through leaks to the outside. Bringing combustion air to the firebox through an insulated and sealed duct solves this problem.

Savings

A home furnace, rated at 80,000 Btu/hour, may operate at a cycle of 50%. To support this combustion 24 cubic feet of air per day, more or less, depending upon how much your furnace runs. Savings will originate from retaining warm indoor room air and particularly from reduced infiltration of cold outside air. Drafts are eliminated or greatly reduced. Savings may be 5-10 cents on the dollar for the heating costs of the typical home.  A heating bill of $200 per month, you could realize a savings of $10-20 per month.