How much chimney to add for elevation

[Hoozie]

To start off, I'm probably overthinking this, but here goes

I'm at ~4200'. I currently have 10' of Class-A Duratech from the ceiling through the attic, and ~6' of DVL with two 45°s from the stovetop to the ceiling, for ~16' total. Englander calls for 15' from the floor, so 12.5' from the stovetop, at sea level.

Simpson says to add a couple inches per joint, then another "30-60%" to the chimney at higher elevations. (gee, real specific there, lol)

ICC/Excel says to add a foot for each 45° piece, then 4% per 1000' elevation.

Doing ICCs math, I'm about a foot short of the 12.5' at sea level equivalent.

My main 'issue' has been losing secondaries towards the middle of the burn. I get smoke out the chimney, and if I shuffle the box around, then I get open flame for a while, with a bit of smoke still. I think a little more draft may help keep the secondaries a bit longer?

So, think I should add the 1' section? Go for broke and add a 2'? Currently I have 3' sticking out right near the peak, so I can technically add the 2' without needing bracing.

Or is there a better rule of thumb for how much chimney you should add at higher elevations?

 

[Grisu]

I would buy some cheap single wall stovepipe from a hardware store, stick that on a nice day on top of the chimney and see by how much that improves the burn. You could try a 2 ft section and if that makes a noticeable difference, proper class A will only make it better, not worse. If 2 ft helps but you feel the draft could still be better, I would try adding 3 to 4 ft of class A.

 

[Hoozie]

I forgot about the ~15" of single wall I still had from my previous chimney "install." I put that up yesterday, and it does seem to draw a little better, but eventually the secondaries still die and I get lots of smoke until I open the air back up.

I do have a 3' section of duratech I can use*, assuming I can get the adapter ring thing off it I'll probably do that, and spend the $100 on bracing rather than new pipe.

I guess one worry I had was getting too much draft if I add 2' or 3', but then I realized unless I add another 15', that probably won't be an issue

*3/4 of the pipe is painted black, so it'll have to go in the attic under the current sections