Length of vertical flu / vent

I have a forced air furnace in my attic. The exhaust vent comes out the side and immediately turns 90 degrees to vertical. The total horizontal run is probably 1-2 inches. Do I need a full 5 foot vertical vent pipe? It sticks up about 4' past my roof ridge and looks like a great way to attract lightening strikes.

You need to follow the manufacturer's instructions and any local code issues. Normally, the inspectors look at the installation instructions (or should) to verify you did it right. Can't get any more specific, but one of the pros may.