stack extension

[Mr Goodwrench]

Building a wood shed which will also house my OWB (see other post my little woodshed) I will need to extend the stack through the roof, question? my HVAC guys say it will need to be class A chimney pipe??? I'ts just single wall now, should I add on to it with class A, or single wall or replace all of it with class A? also how tall should it be above the roof? to the peak or below? Thanks..........

 

[bass_on_tap]

The 10 foot, 2 foot, 2 foot rule. Not sure if this applies to OWB.

http://www.fireplacesnow.com/venting/10-2FootRuleExplained.pdf