i think, (would have to look to know but i think im right) that pellet stoves are allowed a max of 500F plus ambient temp for exhaust temps at the stove coupler (internal) to pass certification and safety testing.
Thanks for the info. I was asking because the stove vent will be directly vented onto open porch with no verticle rise. The porch won't see much activity during winter months, but I was curious as to what to expect if and when I, or others get close to it.
I thought it would need a rise as well, but according to the dealer, with the Harman 'direct vent wall-pass-through kit' you do not need a rise. It is shown on page 13 of their manual in "Tips for choosing the right Harman Pellet Stove." They do say as you mention that a rise is preferable to prevent smoke from backing into house until fire goes out in stove, or until power is restored. They reccomend a power back-up system for that purpose. That I am looking into right now, and the cost involved. Have not done enough research on them yet, but I'm hearing a ballpark range of $300-$500, depending on model and how many runtime hours you want from it. I guess it is not the ideal set-up, but it is the only location that works for me.
Often times what is allowed and what is the best option are not the same thing. You can direct vent them, but it is not ideal. If you are hooking up battery backup, it seems to make the power loss argument a moot point.