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Outside Cold Air Return on Furnace A/C

We just purchased a home built in 2003.  One thing we found that I have never seen before is a 8″ return air duct work that comes from the outside of the house to the main truck on the return…

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We just purchased a home built in 2003.  One thing we found that I have never seen before is a 8″ return air duct work that comes from the outside of the house to the main truck on the return side of the heating A/C unit.  The duct work does have a manual damper which I closed for the time being.  From what I understand, this is to supply fresh air to house.

1.)  When should the damper be open?  All year around – summer and winter?  Should the damper be slighy open?

2.)  Also I found a timer on the side of the heating and A/C unit  (ones where you would use on christmas lights).  Im not sure what this timer is for.  

Thanks   John from Ridgefield Washington.  

Our Answer

I’m not surprised you’re unfamiliar with this type of duct.  It's there to supply fresh air to the heating and cooling system, but is only typically seen in commercial buildings, or in super energy-efficient homes where you have to mechanically exchange inside with outside air to keep it healthy. 
When that's done, it's done through an additional device called an air-to-air heat exchanger – a component by which all heat systems work.  Heat exchangers prewarm air to about 50 degrees before it reaches your HVAC system, so that your system isn't tasked with elevating the temparature of outside air from as low as subzero to comfortable room temperature.  Without a heat exchanger, a system is incredibly inefficient. 
Since this is not a typical HVAC system, you'll need to contract with a good HVAC pro, and have it examined from soup to nuts.  The good news is that you need a pro regardless, in order to keep your HVAC maintained. 

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