i see that some pellet stove manufacturers allow for reduced clearances(18”) from windows if an OAK is used. However, when I look at pellet vent manuals they say that 4 feet is needed. No mention of OAK. Does one set of instructions trump another regarding clearances? Also (and this may be a dumb question) can pellet venting and OAK be put through a foundation wall if it’s above grade (and clearances outside are met)?