Here is a diagram from the IBC boiler installation manual showing the specifications for the venting.

The downward facing pipe is the fresh air intake and the upward facing pipe is the exhaust.  After the renovations, my house is much more air tight and, as a result, the boiler typically runs at 30 to 40 percent of it maximum output when the fan coil is providing heat to the house.  At this low level of output, the exhaust comes out with very little force - "leisurely" is probably a good description.  

The problem is that there's an soffit attic vent directly above the boiler exhaust.  It's probably seven feet away so I didn't think it would be a problem - it turns out I was wrong.  The exhaust ended up getting sucked into the vent by the whirlybird spinning on the roof.  Here's how the whirlybird looks now:

Luckily, I had a short piece of leftover vent pipe that I placed in the 45 degree elbow to direct the exhaust gases farther away from the house.  This spring I'll have to implement a permanent solution.