Secondaries activity related to flue height and draft?

Does anyone see a correlation with the secondaries activity related to flue height? I run a Jotul Castine in a 23 ft interior chimney top vented with an insulated 6" flex liner. I have no problem getting secondaries, but they are like jet burners and are pretty much done in a half hour after the primary air is closed down.

I ran a Jotul F 3 a few seasons back, rear vented and had an in-line plate damper in the horizontal run of the snout. It was pretty hard to reach behind the stove to set it, but I felt it slowed the draft and let more heat out of the stove. I can't remember how active the secondaries were.

The F3 was an easy stove to run and very free-flowing. The Castine is a little finicky, but I have it down good. I am just looking to get the most out of it. I don't have a flue thermometer as there is only inches of vertical flue before the block off plate.

Has anyone added a damper and noticed different stove behavior or longer burn times?

 

I get better performance out of my Buckstove 81 with the inline damper on top of the stove. It just gives me much more control of the air going in and out of the stove. I find that it helps me get a more complete burn and with the primary air open a little more you tend to get more combustion at the fuel as opposed to at the top of the stove by the secondary burn tubes. I think the damper allows you to introduce more combustion air to the firebox without greatly increasing the velocity of the smoke (and heat) exiting the stove. This seems to give me a more complete burn.

 

Good points. It seems to be a fine line to get the secondaries lit without closing it back too much causing a smoulder.

If curious if anyone here has a shorter flue in the 13 - 20 foot range, and how their stove runs.

 

I don't think the line is so fine if you have a pipe damper. It gives you a little more flexibility in the burn without wasting heat. Curious to hear others opinions.

 

I have a shorter stack (11? feet total from floor to chimney cap I think) and it's interesting to run. In short, it's kinda sluggish when it's warm outside and I don't require much heat, and once it hits a certain outdoor temp, it runs fine. In fact, with such a short column of pipe/air to heat up, I find it very responsive once it's cool out. As long as you can outsmart a metal box, you'll be fine.

If you look back on some of my previous postings, you can get an idea on my thoughts of draft and short chimneys.

 

Recently installed a double wall stove pipe damper, it's been 10-12 days now. There is a noticeable difference in how it runs. A few highlights.

Very easy to run in high wind conditions, for controlling the burn, and actually being able to get the wood to catch, rather than the draft pulling so hard that it can't get going. My old cheat was throttle back primary air full, and open door slightly to create enough draft to fire up in high wind. But then with normal size wood, it would take off like a rocket eventually anyways. In 30 mph wind, I keep primary air wide open, damper at half, and it starts up like normal. Once it's established, you can open damper, let it get rolling quicker, then utilize the damper to moderate it again. Or just leave it and watch it walk up slowly.

More complete burn of wood in the stove when the weather is cold, by having a good fire, not a raging fire. The draft will end up being whatever you choose, within reason. A raging fire, a spirited fire, a relaxed fire, or a northern lights/ghost flames whisping in the air fire. It's up to you.

Much easier to keep a lower stack temp, as observed by the flue probe. I will say, with the damper in full open position, it seems to add a slight restriction or slow down (more easily noticed when restarting on coals for example) but not a crazy amount. To me, keeping the stack temp lower than normal while achieving the same temps on/in the stove is obviously a plus.

Hope there's something you find useful in there.

 

Sounds like the damper plate is working out for you.

I ended up installing a damper just above the stove. I only had a few inches of space to fit it in. I ended up forging an extended damper rod with thumb lever.





The burn times seem longer and the secondaries are lasting longer. It works good on cold and windy days. Lever up is open, 1/4 turn is closed? It works great on very cold and windy days when the draft really pulls.

 

Yeah, it's not a very big range of movement to go from no damper to full damper, a matter of degrees. I walk in gentle when settling back the draft, it might take 3 adjustments to make half damper (which is only about a 45 degree sweep).

I wish I would have installed one years ago already. Just goes to show what happens when you step outside conventional wisdom.