Any ideas on why a cold air return vent for a furnace would be connected to a flex pipe that is drawing fresh air from an exterior vent to the basement of the home? Interesting, the exterior vent was sealed with what appeared to be aluminum tape.
The furnace was 93% efficient which had fresh air and exhaust PVC pipes installed to the exterior. In addition, high and low combustion fresh air vents were installed near the water heater.
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Outside air piped to the return is called fresh air/make up air. It’s to equalize the negative pressure on the house from bath fans, drier vents,range hoods ect. By sticking in the return the air gets conditioned before dumping in the house. Without it the outside air will sneak in every crack and crevis,still the same amount but unconditioned
A poor’s man HRV.
Living in my house gives the same, albeit drafty, effect. 
This was a brilliant Idea from CMHC as a means to keep good IAQ in a house. At one point it was the way to go according to them. Now everyone that employed this design has switched out to a HRV, which can capture more than 90% of heat lost through the exchange process.
http://www.cmhc-schl.gc.ca/publications/en/rh-pr/tech/96215.htm
