3 or 4 inch vent pipe kit for Harman XXV pellet?

[BKSinAZ]

Free standing cast iron Harman XXV, single story home.
Directly out, then up thru roof installation.

I would prefer to save money, but do not want problems. 3 or 4 inch?

 

[DAKSY]

If you exceed 15 Feet of run, Harman recommends switching to 4"...
You can switch to 4" anytime in the run, before 15 feet, or you can
switch right at the stove adapter.

 

[smwilliamson]

If you exceed 15 Feet of run, Harman recommends switching to 4"...
You can switch to 4" anytime in the run, before 15 feet, or you can
switch right at the stove adapter.

It's not 15 feel but 15 EVL . Add 5 for t's and elbows, 3 for 45 degree elbows, multiply by 1.5 for each horizontal foot and .5 for vertical and add it up. If you are under 15 3" is fine otherwise increase to 4"