""Boiler has a built in fan for power vent and has a maximum pipe length of 100'.""
That one feature right there is the all important factor I was wondering about.
In the past I have heard of too many folks installing boilers and other things requiring venting but not designed for forced air lateral run outside air intakes and exhaust. only to fins out that they had to have positive flow chambers designed
I can full well appreciate not wanting a hole cut in the roof