Drop from an 8" to a 6" Stainless PreFab chimney?

[RedOak]

OK, I would some input from the soapstone crew. I have the Hearthstone Mansfield that I installed at the beginning of this heating season and am getting good heat output and decent extended burns. My only concern is my stack temps can run in the 600-700+ degree range for an hour or two after I crank it back and get the beginning of my secondary burn. Good rolling flames, plenty of heat (400-475 stove top). After an hour or two I end up with the blue phantom flames from the secondaries and my stack temps drop to 400-500 range. I have extremely good draft - so good that I ended up with two dampers in line - so I am wondering if I am loosing an excessive amount of heat up my chimney. The stove is new and all gaskets are good.

So my question is, do I switch from my 8" SS chimney to a 6" like it was designed for? I can't be the only one who has dumped a Mansfield into a larger chimney. It isn't really broken, so do I try and fix it anyway?

 

[crazy_dan]

with 2 dampers in the flue I don't believe yo are losing much heat out the stack. As far as going with a 6" it is up to you if you are happy with the heat output and performance of the stove then I wouldn't spend the money. and the higher than normal flue temps if the thermometer is below the dampers then it could just be holding the heat that would normally go out the stack. I am wondering what the temps are above the dampers?

 

[RedOak]

The probe thermometer is above the damper section of pipe

For all I know I could have been running high stack temps for the last 20 years and not known it. I just started monitoring the stack as it is a completely different beast than the VC Defiant I was running prior.

It just seems like I am one of the few who see this high a temp...

 

[swestall]

I'd not worry about that at all. The 8 inch area is actually larger and with the 6 inch output on the stove, you are likely to have a weaker not stronger draft. What was happening without the in line dampers? That's a really strong draft if you close down two dampers and still have good pull.
What is a good overnight burn?
How high are the dampers and the probe thermometer? It doesn't seem like those temps are really excessive at all.

Isn't the Mansfield a dream? This morning when I drove down the driveway to leave for work, I glanced up at the stack and could see just a hint of heat wave. Every time its like that; a far cry from that other stove. Every time I'd drive down the drive with it there would be some level of smoke; especially in the morning when I didn't have a few hours to get it Everburning to some degree.
What a relief it is to have a stove that heats like a bear, runs like a champ and leaves you feeling secure that you aren't dumping creosote in your stack. Ya gotta love'm....

 

[RedOak]

I just assumed I would pull a stronger draft by the shear volume of the larger 8" chimney. Hmmmm...good point.

Without the dampers I had a hard time getting a decent burn time and with the recommendations of people on this forum I installed a probe thermometer about two feet above the stove before it transitions to class A double wall. The two dampers are below this, not ideal but I had few choices at the time. I have good overnight burn, plenty of coals on the morning and a toasty house unless it gets windy and in the single digits. That's why I am hesitant to change my formula - its working out pretty well as it is. I am just concerned seeing the probe that close to the red zone when everyone else seems to have much lower temps. Saturday night I loaded it up with some really dry oak and it seemed like it took forever to bring the stack temps down to what I am comfortable with. Almost considered plugging the secondary inlets with gloves. I bet my chimney is pretty clean though!

I love the Mansfield now, but what a difference from cast iron. I had so many "bad" habits to break during the transition and was frustrated after putting out that much coin and not seeing that much of an improvement over the VC. You seemed to have made the switch much better than I.

 

[swestall]

Well, we just have to lay back now and ride the learning curve. There are a lot of differences. One thing is getting up to 450-500 and staying there. I find I can keep the secondary burn going shut down all the way once it is hot. And, it will hold 450 after a while. At 450 it is heating the house very well, more so than the Defiant did running at 500-600: I think that is because the Defiant really goes up and down over and over while the Mansfield gets there and stays there.
Of course, running shut down all the way with temps of 400-450 isn't flat out but it is good for the long burn. BB said today that he runs with the Englander at 1/4 to 1/8 if I interpret his comments right. He said that he gets a good burn time, a bit hotter stove (it is steel though) and he has less coals. I do have many coals burning closed down.
The Defiant was so bad that this is a dream. And, it operates pretty easily versus most others I know of. I almost went for the Equinox or PE-T-6. I'm glad I got this.
Tonight when I came home there were very few coals as it was warm here today and I only put three splits on the fire to burn during the AM then burn off coals before I got home. I scooped out the ash, raked up some coals that were left and broke half a super cedar in three pieces. Over that I put a couple pieces of small split, and three medium splits with one fairly large on top. I lit it off with a small piece of paper and let it go: in 30 minutes it was all ripping. Quite a difference from struggling with kindling, paper and all.
So, now its time to experiment with draft settings and just see what works best with that stack. Don't let a bad burn frustrate you, just tweek things and move toward your optimum from there.