Our plan was to use a 3/4" bit and drill a series of several holes around a 6" circle and chip out the middle. BUT, we found this nifty little tool to rent at one of the local rental places. It's a 6" core bit that's 15" long!!!! It has a compressor-like attachment that suctions the drill contraption to the wall, and a vacuum and water attachment that sends water to the bit (see the hose running to it?) We were finished drilling both holes and packed up and ready to return it in less than 2 hours. SWEET!
In the picture below you can see one hole already drilled on the right, and Kenny is working on drilling the second hole on the left.
Here's a close up of the system.
Here's a close up of the piece after we pulled it out of the hole. You can see the 2 5/8" thick ICF foam on either side and the 8+ inches of concrete in the middle. Not to mention that we also had 1" thick of stucco from the exterior that's not shown, and 5/8" of drywall from the interior that came off the foam when we pulled the piece out. 
What's an HRV? Well, basically it's a way to get fresh "make up" air into the house. Most of the time, houses get fresh air from incidential air infiltration - leaks in the home's envelope. Since our house is so tight, there's no way for us to get fresh air except for opening the windows - which is not very energy efficient. So, an HRV brings in fresh outside and and exhausts stale interior air. When the two airs pass each other, there is a heat exchanger that takes the heat from the stale air exhausts and gives it to the incoming fresh air. This is a way to preheat the incoming fresh air so that it doesn't affect the temperature of the house and it makes your heating systme work less. This is an energy efficient way to get fresh air into the house during the winter and hot parts of the summer when the house is closed up.
