Tale of Two Stoves

[Tomasacio]

My problem is a relatively new Jotul 500 Oslo stove that in the past 2 years has begun to over-fire and run away on me with regularity. However the story has its nuances.

In November of 2001 my wife decided that it was time to retire our trustworthy Consolidated Dutchwest stove and get something a bit more fashionable. We decided on the Jotul. We actually got two, one for the basement and one for the main floor. We also decided to have our two tile flues stainless steel lined and insulated. The flue from the basement is about 35 feet in length while the flue for the other stove is about 25 feet. The only difference between the two is that I had the flue installers extend the s/s liner etc down to the original clean out door in the basement and T-connect the stove exhaust to it. The basement stove connects to the flue liner at the bottom, while the stove in question has a ten foot drop to the bottom(plugged with fiberglass insulation to stop air flow from clean out door). I did this so I could clean the flues myself without having to move the stoves out and back every year as they suggested.

Within the past two years the main floor stove will occasionally get to roaring and be impossible to slow down with the single air flow lever provided. The stove in the basement although not used as much performs always perfectly. I have heated with wood for about 30 years now and never felt so hopeless with a fire. I have taken off the shroud that covers the air vent lever twice to make sure it works properly. It does. I have repeatedly fiddled and adjusted the ash pan door to make sure I wasn't leaking air there. This stove just acts like it has an unlimited air jet and it seems to be from the lower right corner of the stove front, where the front door and ash pan hinges are; they are not loose, and the seals appear to be functioning properly.
The event appears to get started after loading new wood into the side loading door; the fuel gets a rush of oxygen and starts a sucking that I cannot shut down. It roars like a chimney fire and my wife more than once has tossed water onto it to slow it down since she does not feel comfortable going to bed the way it is.

There are a few other points that I could add but none seem significant to my problem right now. Also this was not a problem the first 3-4 heating seasons, it developed with time. It is also not a constant but seems to becoming more regular. My stoves do not have flue dampers because it was recommended not to, though I've always used them in the past. I cannot help but think that there is something not right with this stove but Jotul does not give me any contact information that I can find for me to look into this.

Thank you for any help you may provide. T

 

[webbie]

It certainly sounds like an air leak, but then again it could be an over drafting chimney. If it were mine, I WOULD install a stack damper just for experimentation, and then perhaps find a "set it and forget" it setting - possibly only a little closed.

Here is a way to test for air leakage - use a butane lighter of sorts and hold it near where the panels mate - if it gets sucked in hard, then you do have an air leak. Another way is to put a very bright light inside the unit and turn all the lights off and see if you can see any light in the joints.

If and when you locate air leaks, these are very easy to fix. No need to rebuild the stove (in most cases). Check back here after you explore a bit.

Note that draft can vary extremely with weather, so the fact that it didn't happen before is not a big variable....you may still have an over draft.

Also, explore the path for the secondary air in that stove. Is it fixed, or does it vary with the draft setting of your lever? Some stoves have a fixed (always on) secondary air inlet, and maybe yours is letting in too much air and acting as primary and secondary (damper may fix this also).

 

[begreen]

I would start with a solid metal cap on the bottom of the pipe. I don't trust a wad of fiberglass for a tight seal. From there on I would follow Craig's advice. Look very hard for an air leak. I would start with a very close inspection of the ash pan door gasket and the seal where the ashpan is bolted to the stove body.

 

[Gooserider]

Echo the need for a SOLID seal on the bottom of the flue pipe, not a hunk of fiberglass.

Next I would do a "dollar bill test" all the way around the doors paying particular attention to the areas you think are leaking... Have you changed the gaskets on the doors lately? Gaskets ARE "wear items" that need periodic replacement, typically every 2-3 years w/ regular use.

Another thing I would try if the above doesn't solve the problem is, when the stove is running away, get a stick of incense (or a cigarette), turn off as many blowers and fans as you can so that you have still air around the stove, and slowly wave the incense around the stove (Invocations to Hestia, Goddess of the Hearth are optional at this point %-P ) and see if the smoke gets pulled into any cracks or leaks - you have a cast iron stove, and it's possible that you have developed a bad seam that's leaking air into the firebox.

BTW, your wife throwing water in the stove is a very bad idea - it could damage the stove, and also has the potential to be EXTREMELY dangerous for her - do a search on "BLEVE" for an explanation as to why this is...

If she must throw something on the fire to slow it down, try baking soda.

Gooserider

 

[Tomasacio]

Thank you all for the quick responses. To start, the water thing bothered the heck out of me too, I will buy her a big box of A&H;to use next time. I will try this weekend to check for draft leaks with a flame and reexamine my gasket seals and hinges. I WILL put a damper in the short pipe as I have always felt that helped me control my burn more finely; why do they recommend NOT installing one? Where can one find a metal end cap to fit over the 6" flue liner? However I experimented and thought that the chimney draw was WORSE with the end open and improved dramatically when closed (plugged with fiberglass). Maybe I should unplug the end of the flue liner when the fire begins to run, that might at least slow the draft? What do y'all think? Maybe even open the ash door too?

What exactly is "overdraft"? I always thought that if I had a high quality "airtight" stove I could choke it off by closing my air supply controls. I was not aware that there was a secondary air supply. How might I go about tracking this down? Would it be indicated on the schematic?

If this is a problem with draft why does the other stove with the longer flue not do the same thing? I hesitated to call the dealer because I am not sure that they would be able to add anything to this discussion.

Any further thoughts gentlemen. I greatly appreciate all the good suggestions. Tom

 

[Gooserider]

Thank you all for the quick responses. To start, the water thing bothered the heck out of me too, I will buy her a big box of A&H;to use next time. I will try this weekend to check for draft leaks with a flame and reexamine my gasket seals and hinges. I WILL put a damper in the short pipe as I have always felt that helped me control my burn more finely; why do they recommend NOT installing one? Where can one find a metal end cap to fit over the 6" flue liner? However I experimented and thought that the chimney draw was WORSE with the end open and improved dramatically when closed (plugged with fiberglass). Maybe I should unplug the end of the flue liner when the fire begins to run, that might at least slow the draft? What do y'all think? Maybe even open the ash door too?

What exactly is "overdraft"? I always thought that if I had a high quality "airtight" stove I could choke it off by closing my air supply controls. I was not aware that there was a secondary air supply. How might I go about tracking this down? Would it be indicated on the schematic?

If this is a problem with draft why does the other stove with the longer flue not do the same thing? I hesitated to call the dealer because I am not sure that they would be able to add anything to this discussion.

Any further thoughts gentlemen. I greatly appreciate all the good suggestions. Tom

There are two or three reasons why chimney dampers generally aren't reccomended on EPA stoves..

1. Most people don't need them! A stove with normal draft levels, installed properly, etc. shouldn't need a stack damper, and often one can be misused to cover up other problems (such as an air leak in the stove) by treating the symptom of over-firing rather than looking for the "root cause" problem.
2. If you have a low draft setup, a chimney damper represents an additional flow restriction, even when open.
3. Your stove is designed to have a certain minimum amount of airflow through it at all times in order to ensure clean burning and compliance with EPA standards. The fear is that a stack damper would be mis-used to shut the stove down below this point, probably in an effort to extend burn times, which would cause it to go into the creosote and pollution producing "smolder mode" of most smoke dragons.

Your local stove shop should be able to supply you with a cap - make sure you get as exact a measurement as you can on the opening to ensure that you get the right one. If you just have the bare end of the liner presently, you might also need to get the liner termination adapter as well.

Over draft is what it sounds like - your stove was engineered with a certain amount of draft in mind - regrettably most stove makers won't tell us just what it was. Having drafts that pull a lot more or less than the reccomended amount can cause problems, appropriately referred to as over and under drafting, respectively.

Gooserider

 

[Tomasacio]

Thanks Goose, I'll be working on it T

 

[Tomasacio]

Ok so if any one is following. I covered the stove pretty carefully with a candle flame. I caught a slight draft on the hinge side of the front door. How severely could this be magnified in an over draft situation? , which is what I think I am dealing with given the discussion here. I have a new narrower, insulated flue that could super heat. Still not sure why I do not get this same phenomena from my twin stove in the basement but my next step is a damper at the stove exhaust and a real end cap on the clean out end of the flue liner. Tom

 

[MountainStoveGuy]

your twin stove in the basement is in a different pressure plane in the home. Basement stoves will ALMOST ALWAYS act different then the exact same stove installed in the main floor of home. The basement has more negative pressure then the main floor making the stove have to work harder to draft. I agree with the above statements that this is most likely a overdraft situation on the main floor, expecially when i read about a 25' chimney.....

 

[Codeman812]

BLEVE is a very bad thing, we firefighter really cringe with the word

BTW, your wife throwing water in the stove is a very bad idea - it could damage the stove, and also has the potential to be EXTREMELY dangerous for her - do a search on "BLEVE" for an explanation as to why this is...

If she must throw something on the fire to slow it down, try baking soda.

Gooserider

 

[Gooserider]

BLEVE is a very bad thing, we firefighter really cringe with the word

BTW, your wife throwing water in the stove is a very bad idea - it could damage the stove, and also has the potential to be EXTREMELY dangerous for her - do a search on "BLEVE" for an explanation as to why this is...

If she must throw something on the fire to slow it down, try baking soda.

Gooserider

That is my understanding Codeman, can you expand any further, particularly If I'm correct in my understanding that throwing water in the stove is a scenario that carries a significant risk to it? - If I'm right I'd like to know a bit more so I can better describe why in the future, and if I'm wrong, well, it's good not to give bad info :red:

Getting back to the original question, it takes surprisingly little leakage to cause an overfire situation - when I first put in my Encore, (It is also on a 25' first floor chimney) it was getting much hotter than I liked on my first full load fire, even with the air turned all the way down. Doing the "dollar bill test" I found one door gasket that would touch the bill but not really put any drag on it, and that the bottom edge of the ash door wasn't closing tight. Fixing those two leaks were enough that the stove now responds much better to the controls, though I am thinking about where I could put a butterfly damper given that I don't really have any connector pipe in my setup. I find that while my air control works, other than starting from cold, nearly all of the control action is in the first little bit of movement. Looking at my air control from the side, minimum air is about 4:00, maximum is about 10:00 - after putting in a full load and charring it w/ full air, I can go from "embers w/ an occaisional flame" at 4:00, to "90% of the flames I got on max air" at about 6:00. i would love to see if adding a damper would give a wider range of control useage.

Gooserider