Overhead furnace vent pipe sizing question

[martincc]

Hello, I just picked up a used Olsen KAS100 overhead has heater for my detached garage. I have a gas fitter coming to pull the gas permit and install the gas line. I plan to do electrical myself with a city inspection and also install the roof vent myself. My question is regarding the roof vent. The outlet on the furnace is 6", do I need to run a 6" vent or can I go to a 4"? 4 seems to be more available here in Calgary AB. Also, had to find info on codes here. The exhaust for the unit is straigt up, can I just run the pipe straight up from the unit, through the roof, or does it need a bend for some reason? It will be 2 ft away from anything at its final point, low sloping roof. Anyone have any links to manuals on this unit, hard a hard time finding anything. thanks! If anyone is from Calgary, where is the best place to find vent pipe?

 

[csp]

You can step up in sizes, but never down. If it's 6" coming out of the heater it needs to stay 6" or larger all the way out.

 

[martincc]

any idea where I cna buy this? Seems impossible to find in Calgary.. home depot does not sell it. Is a stright up design ok, no bends are necessary?

 

[csp]

Find a HVAC supply house.

Straight up is preferred.