What kind of a meeting was this? The eff. does not drop due to pulling combustion air from with in the building vs outside. Think about it , the combustion air has no thing to due with eff. of the furnace. The eff. of a furnace has to due with how much of the total heat can be taken out of the exhaust gas along with other factor's. The main way that GAMA ( the company that determine each and every furnace's eff. independent of any manufacture) is the temp of the flue gas. On a high eff. furnace the flue temps are in the 85-100 degree area and a 80plus furnace the temps. range in the 300 range. I might be a little off on the temps but that is the easiest way to explain. I hope this helps.

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Well thats my 2 cents.
Brian Kelly
Kelly Home Inspections