Near overfire

[BradleyW]

Hi, just had a little scare last night that I thought you guys could shed some light on. We loaded up the Jotul F55 about 80% full and things were going as planned. We had shut the air down around halfway, the stovetop temp was in the 550 range and the stove pipe was around 450. We then shut the air down to around 25 or 30%. This is usually where we end up because we have a poor draft--16 foot chimney with two 90 degree turns. About five minutes later I go over to the stove to check it one more time and the stove is in near overfire: stove top at 800 degrees, stove pipe even hotter. I immediately opened the door all the way (thank you, Hearth.com) and the fire cooled down. Fortunately I don't think any damage was done. There was no glowing red, only a little "new stove" smell from the high temps not achieved previously. I just don't know what happened. When I looked at the wood about 30 minutes later it looked like one of the splits was almost disintegrated, while the others looked normal, like they were still mostly solid. The wood was a hardwood mix, a couple oak, probably mostly maple. Any thoughts on why that happened? This is our second season with the stove and we've never seen anything like it.

 

[prezes13]

Maybe this load of wood was drier what you were used to burn? Did you load it diftently than usual? If you are used to load e/w and loaded n/s there will be difference. Was it colder outside? That would increase a draft there is a lot of possibilities.

 

[TheRambler]

What was the stovetop temp at reload. If it was already at 550 when u shut the air halfway then that sounds like you loaded when the stice was quite hot/ onto a very large coal bed.

If that was the case this would explain what happened; as the wood off gased rapidly and the stove went into inferno mode with the air still open a good bit.

 

[BradleyW]

We loaded the wood like we usually do, n/s, and the stove wasn't as full as we sometimes load it. The wood was from the same lot of wood we've been using all fall, so while I can't attest to the individual pieces, as a group the wood has been pretty consistently 20% moisture on a fresh split. The stove was actually pretty cool when we reloaded, around 300 degrees.

 

[Huntindog1]

What was the stove pipe temp? You say even hotter than 800. That tells me alot of heat was flushed up the flue.
Make sure your dont load a large load of high BTU fuel on a very hot coal bed. Its a feel of your pants kind of thing
if you sense ths are firing up faster and might go too high shut the input air down quicker. Sounds like the draft is fine.
As alot of draft issues clear up when it gets colder.

But 800 stove top temp isnt all that of an issue but if the pipe was hotter than that, then that is an issue, as sounds like the door didn't shut good or something like that. As it points to too much air coming in. Sure 800 stove top your need to slow it down.

 

[rippinryno]

this is wierd, i've not actually concerned myself with overfire. I'm curious to know how a person could identify this so I'm aware in the future in case this happens. I've been heaping my stove and letting it burn with pretty good draft. Since my stove has a blower that blows around the firebox, i wonder if this prevents over fire? That or else the stove design doesn't allow for it. My stove has 2 knobs on the front that i can use to adjust draft pull. I usually have them about halfway open so that the stove is constantly feeding the flaming and running at a fast and hot pace. When i dampen it down, i tend to get more smoke and less heat.

i am glad i read this as it's something that i think many can learn from, so many people just loadn and load and then walk away. My stove install is only 1 month old so I tend to not reload at all if i know i'm going to be leaving anytime soon.

 

[Nick Mystic]

When my Jotul F600 is 300F coming off a burn I still have a very large and hot coal bed. I usually don't reload until the stove is a bit cooler unless it's down in the 20s and the house is cooling off fast without a hot fire burning. Once things start to get out of control the temperature can climb extremely fast, which is why I always keep a very close eye on things after a reload. A couple of experiences like you described usually makes an impression on folks in this regard. Good luck.

 

[branchburner]

stove top at 800 degrees, stove pipe even hotter.

How are you measuring pipe temp? Is this an external, single wall temp or internal?

 

[BradleyW]

External single wall temp with a magnetic thermometer. Not sure what the high temp is on it but I think it was basically maxed out.

 

[branchburner]

So to me a flue temp that high hurts the theory that the stove simply "took off" as a result of a hot reload. I don't see the flue temps spiking to those levels without another additional cause, like either a chimney fire or more likely an excessive influx of air that both stoked the fire AND pushed the extra heat up the flue, like Huntingdog said..

Is it possible after the reload that a coal or small piece of wood got lodged in the door when it was closed, leading to a temporarily faulty seal? That could have provided the "blast furnace " conditions and super-hot flue. Otherwise, it seems odd this would suddenly occur when your reloading procedure and type of fuel was nothing out of the norm.

I assume normally your flue temps would drop to the 300f range at 20-30% air supply?

 

[Woody Stover]

Has it got an ash pan door? Could it have been not completely closed? Did you look at the door/ash pan gaskets? Air intake control couldn't get dislodged somehow, could it?

 

[BradleyW]

So to me a flue temp that high hurts the theory that the stove simply "took off" as a result of a hot reload. I don't see the flue temps spiking to those levels without another additional cause, like either a chimney fire or more likely an excessive influx of air that both stoked the fire AND pushed the extra heat up the flue, like Huntingdog said..

Is it possible after the reload that a coal or small piece of wood got lodged in the door when it was closed, leading to a temporarily faulty seal? That could have provided the "blast furnace " conditions and super-hot flue. Otherwise, it seems odd this would suddenly occur when your reloading procedure and type of fuel was nothing out of the norm.

I assume normally your flue temps would drop to the 300f range at 20-30% air supply?

This seems like a possibility. Blast furnace is a perfect description of what happened. It basically seemed like we had never turned the air down at all, even though we were slowly shutting it down like always. The other thing this made me think of is what if something got into the air input and when we shut it down that last time made that not function properly and essentially open it all the way back up? Is that even possible?

 

[BradleyW]

Has it got an ash pan door? Could it have been not completely closed? Did you look at the door/ash pan gaskets? Air intake control couldn't get dislodged somehow, could it?

There isn't an ash pan, but maybe it was the air intake control. It is working correctly now, but maybe it was dislodged temporarily?