Air to Air Heat Exchanger Expectations
 

Since my home was built to a higher energy standard of the day (late 1990's), and supposedly tighter construction methods, they installed a fresh air duct to the heating system. When it comes on (via a timer), the high cfm bathroom fan in the upstairs bathroom begins. It was set for 10 minutes every three hours. I thought that was a bit excessive.

After I had a energy audit done with the blower door test and high tech thermal imaging device, I know that the house is not as tight and insulated as it could be.

With that in mind what should one expect with a heat exchanger? I found one with 50% efficency on a Mitsubishi unit for sale locally. The unit is only $45 but after reading this, maybe I should make my own?

You can build one with efficiency as higher than 90%.
DIY ventilation heat exchanger

You can calulate the heat you're loosing via that fan running. It might be a lot less than you think. A DIY HRV would improve things though.