Cause of occasional poor secondary combustion - Mansfield

[mikeathens]

Not sure if this has been discussed before; if so, I wholeheartedly apologize. Couldn't find anything with a search...

This is my first real use of my Mansfield, since I got it in the latter (warmer) part of last season. I am a total psycho when it comes to checking the chimney for smoke, and have noticed that I've got pretty good smoke coming form the chimney about as often as not. I'm always tweaking the primary air to try to optimize things, and sometime don't have any luck correcting the "problem". Don't get me wrong, this puppy heats great, and gets me a good 8 hour sleep, even when temps get in the teens (if my daughter wasn't kicking me all night).

A couple of things - I don't have a moisture meter, but I am assuming that my wood is dry (mostly red oak, walnut and black locust, down for at least a year, and split and stacked under roof approximatley 12 months ago - never would suspect this, but know it will come up if I don't mention it.) Chimney is straight up - 4' of single wall connector, and 12' of prefab above that. I have a flat roof, so only about 2' of the chimney is "enclosed"...10' of it is completely outside.

I've noticed that primaries respond better to about a half load of wood. When I load it to the rafters, I get flame out the sides and front of the load, but there is no activity from the secondaries. I started messing with my flue damper last night, and it appears to be helping somewhat to "slow" the burn. Oddly, even when there seems to be a lot of nice secondary action going on, I still occasionally see lots of smoke...huh??

I rewatched the "top down method" video (can't remember what that Canadian video's called) and noticed when she's starting a new load from coals, EVERYTHING is raked to the front of the stove, leaving a nice bare floor. Could the fact that I leave coals over the entire bottom of the stove be causing some of my problems (like making the wood in the rear smoulder)? ...OR... Could the fact that almost ALL of my chimney (other than connector pipe) is outside be causing problems?

I had borrowed a draft meter from the stove shop last year when I installed the stove (I can't remember the reading), but it was within spec, so I didn't have many concerns with draft at the time. could be a cheap-o worthless meter, I guess (plastic crap with little floating balls in it).

Any ideas? Any others have this same thing happening and figure out the culprit? Granted, it was only about 45 out last night, which I'm sure didn't help, but I have noticed this in colder whather also.

FYI, my typical operating scenario is 400-600 in the stack (probe thermo), and 400-500 stove top. I usually have to leave primary air open 100% for 30 minutes, and the slowly ratchet it down until it's about 25% open. If I close it all the way, I'm almost sure to kill the fire.

 

[struggle]

It kind of sounds like a lack of draft to me. I have no problems getting secondary burn with a 25' chimney liner plus the additional 4' going to the stove.

When I reload a leave the coals spread out unless I am getting to many coals then I rake them forward. For over night burns I rake them forward and load.

As for smoke I always seem to have a short wispy trail of it coming out most of the time it is burning and only when it gets completely down to coals does it stop. I have tested my wood with a el-cheapo harbor freight meter and it shows 10% and on wood I was having problems getting heat out of it showed 24% so it seems to be reading right.

I think the smoke you are seeing or at least I see is from the hot air hitting the cold air and it creates a little steam action. I only cleaned my chimney once last year at the end of the season and brushed only about 3/4 of a gallon of very fine black ash out of the pipe.

I like to run the stove in the 500-525 range. My probe temps on crazy secondary burn can hit 1000 if I let it run.

When I reload the stove in the morning I usually take a few scopes of ash out and the spread the coals and fires back up with only leaving the door open for less than 5 minutes. I also use a pipe dampener for once it is running strong.

 

[mikeathens]

When I get my addition put on the back part of the house, it will include a 10/12 pitch roof. That means the chimney will run through insulated area for about 14' with only 3' or so with outside exposure. Unfortunately, that's a few years off. Seems like when I run the stove hot, it will do really well.

Those chimney temps you are getting a a little hot for my taste - though I'm sure I could replicate that. About how much is your primary air contol open when that's going on?

 

[struggle]

When it gets to 800 on the chimney probe I cut the primary all the way closed and it maintains secondary for quite some time after that until it is just a pile of coals. I can even just rake all the coals into a pile and secondary will take off again but just in solid blue flames lazy like.

I like to do a near 1000 degree to serve as a chimney cleaning I guess you could say. Once it hits that temp it the stove will soon climb to 600 if left alone but I will aim a tower fan toward it to cool the stove down so it does not hit 600.

I normally after loading will taper the primary back once the probe reads 650-700. My cruising probe temp will usually be around what the stove temp top is or slightly above that so 500 on the stove would be around 550 on the probe with active secondary burn.

 

[JonOfSunderland]

I posted this same exact problem last night...

https://www.hearth.com/talk/threads/30127/

The post has the details of the situation, but for me it appears to be a slightly wet wood situation. I also regularly run 1000 degree flue temps to "clean" out the chimney. Then when the stove gets up between 500-600 stove top I slow it down.

 

[mikeathens]

Well, thanks for the replies. I guess I do think it is a draft issue now, since I've really thought about it. Though I am buying myself a cheapo moisture meter for myself for christmas just to be sure. I don't expect to find that my wood is >20% moisture content.

Does anyone know how to remedy this issue, or am I just stuck with it until I get my new roof on? I literally have 10' of my total 16' chimney outside. It is braced and I think it would be a real task to add anymore pipe sections to it (I have nothing else to brace additional sections to). Any advice? Anyone know how to either add an insulating "blanket" to the existing chimney, or otherwise improve draft? I've briefly thought about an insulated chase, but discounted that right away since i'd be tearing it right back down in a few years. Plus, it would look super-stupid.