Usually direct vent means it exhaust vents into the living space, as in there's no flue. They sometimes say its 100% efficient because there's no loss out the flue. Of course you are also getting 100% of the carbon monoxide.
All furnaces with blowers have a heat exchanger to keep the carbon monoxide out. Even the run of the mill 78-80% efficient ones built in the last 25 years.
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