The Oslo Nuclear Reactor

Oct 24, 2017
34
Adirondacks
I know you guys love your Oslos’s but I’ve got a story to tell! Scared the crap it fo me! I loaded my stove before bed two half burned white oak logs close to charcoal state but still holding together. Loaded an additional 3 big splits of oak. Primary was 1/2 open and left it that way for 5 minutes. Closed the primary completely an watched the fire grow normally about 20 minutes late I had great secondaries and some yellow flame on the logs but not much at all. So far so good. Everything normal. I fell asleep in my chair and woke up about 1/2 hr later to blistering heat and what looked liked a nuclear reactor in meltdown. Remember primary was closed. Everything in the firebox was burning at once. The flames filled the entire firebox and looked like plasma more than flames. Secondaries were turbulent, blue and blowing HARD against the front glass. All the wood was being consumed at once in a conflagration. A fire that should have lasted 6-8 hrs was down to coals in 30 minutes. Never saw this before. Not with this F500 or my previous F600.

I have a 30’ straight run of double wall up through my roof of the great room. Temps are hovering around zero F outside. Like I said primary was closed. This was all secondary air. I don’t think Jotul had this situation in mind when they designed the stove. Gaskets are all good. The stove was well behaved this afternoon when temps were about 25F. I did nothing unusual. This has to be an overdraft! Never seen one before but I can’t imagine it can get much worse. No signs of any parts of the stove glowing. Certainly scared the sh*t outa me. Should I install a key damper to control the draft?
 

begreen

Mooderator
Staff member
Nov 18, 2005
79,592
South Puget Sound, WA
Yes, with a 30' stack it sounds like a key damper is needed.

What was the stove top temp during this flame out? Did you notice the flue temp?
 

EatenByLimestone

Minister of Fire
Jul 12, 2006
7,159
Schenectady, NY
Yup, was cold last night. I'm up at schroon, so probably not too far from you. My load last night went up fast too, but with not as much excitement.
 
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Ctwoodtick

Minister of Fire
Jun 5, 2015
1,123
Southeast CT
It always a good idea to load wood only once stove burned down to coals. Sounds like you put in a good amount of wood when stove top was already pretty hot. This can lead to what you described (along with 30ft being a very tall stack).
 
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SpaceBus

Minister of Fire
Nov 18, 2018
3,023
Downeast Maine
Just turn down the air sooner next time. A damper wouldn't be a bad thing either.
 

EbS-P

Member
Jan 19, 2019
206
SE North Carolina
I’ve been wondering if you can overfire with the primary air full closed. Even with a flue that meets draft specs it seems possible.
 

Sawset

Minister of Fire
Feb 14, 2015
624
Palmyra, WI

SpaceBus

Minister of Fire
Nov 18, 2018
3,023
Downeast Maine
I reload hot on my not Jotul Oslo and as long as I'm quick with the air control it is always as controllable as ever.
 
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DBoon

Minister of Fire
Jan 14, 2009
1,144
Central NY
What SpaceBus said - if you are going to load with a lot of coals in the stove and/or a hot stove condition, you have to be aggressive about turning it down early. I had this happen once or twice and had the stove top get to 750 degrees F for a half hour or so with blower on maximum, and it is no fun.
 
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bholler

Chimney sweep
Staff member
Jan 14, 2014
19,400
central pa
I know you guys love your Oslos’s but I’ve got a story to tell! Scared the crap it fo me! I loaded my stove before bed two half burned white oak logs close to charcoal state but still holding together. Loaded an additional 3 big splits of oak. Primary was 1/2 open and left it that way for 5 minutes. Closed the primary completely an watched the fire grow normally about 20 minutes late I had great secondaries and some yellow flame on the logs but not much at all. So far so good. Everything normal. I fell asleep in my chair and woke up about 1/2 hr later to blistering heat and what looked liked a nuclear reactor in meltdown. Remember primary was closed. Everything in the firebox was burning at once. The flames filled the entire firebox and looked like plasma more than flames. Secondaries were turbulent, blue and blowing HARD against the front glass. All the wood was being consumed at once in a conflagration. A fire that should have lasted 6-8 hrs was down to coals in 30 minutes. Never saw this before. Not with this F500 or my previous F600.

I have a 30’ straight run of double wall up through my roof of the great room. Temps are hovering around zero F outside. Like I said primary was closed. This was all secondary air. I don’t think Jotul had this situation in mind when they designed the stove. Gaskets are all good. The stove was well behaved this afternoon when temps were about 25F. I did nothing unusual. This has to be an overdraft! Never seen one before but I can’t imagine it can get much worse. No signs of any parts of the stove glowing. Certainly scared the sh*t outa me. Should I install a key damper to control the draft?
Yes with a straight up flue that tall you need a key damper maybe 2.
 
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firefighterjake

Minister of Fire
Jul 22, 2008
18,971
Unity/Bangor, Maine
Not much I can contribute that hasn't already been said . . . i.e. when to load, when to turn down the air, flue damper, etc.

Usually the stove is pretty controllable, but once in a while (2-4 times a year) I see the Oslo go thermo-nuclear on me (usually when I stuff it with smaller, high BTU wood too early). When this happens I can get some control by using a small piece of aluminum foil to partially cover the air inlet on the back bottom of the stove . . . then it gets pretty psychedelic as the flames typically turn blue to violet and go all slow-mo like.
 

begreen

Mooderator
Staff member
Nov 18, 2005
79,592
South Puget Sound, WA
I kept a big foil ball to stuff into the Castine's outside air intake for this purpose. Like you I only needed it a couple of times and they were when I was experimenting and learning the stove.
 

webby3650

Master of Fire
Sep 2, 2008
10,521
Indiana
I remember those days of the often times uncontrollable and unpredictable Stove. I’ve been super spoiled by my Blaze Kings I guess. Load it and forget about for a LONG time.:)
One thing to check: Fine ash can accumulate at the back of the ashpan floor, it can get really compacted overtime and prevent the ashpan door from sealing as well as it should. It’s hard as a rock and can be overlooked. Just a thought.
 
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EbS-P

Member
Jan 19, 2019
206
SE North Carolina
With the short legs and tight clearance to the firebrick I’m not sure I could even reach my air intake when the stove is roaring hot. I’ve considered practicing on a cold stove to see if it’s even possible. Probably should.
 
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webby3650

Master of Fire
Sep 2, 2008
10,521
Indiana
How high did the temperature on the stovetop go?
 

edyit

Minister of Fire
Nov 30, 2014
819
Wilmington NY
yeah it was cold here last night, -3F this morning, combine that and a tall chimney and as others have said you'll want a key damper to tame things
 
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Oct 24, 2017
34
Adirondacks
Thanks all! I will wait until the firebox cools down before a reload. I reloaded earlier than usual to get to bed. I will put in a key damper for emergency use. I felt helpless. The use of really dry oak made the situation worse in prolonging the burn and adding to the temperature in the firebox. I inspected the stove and all looks good. No cracks.

My wife cleaned the stove and put the thermometer in the middle of the cook plate not in the corner where Jotul recommends it. It was reading 560 the borderline between green zone and red zone. I didn’t have my IR thermometer with me for accurate temps. I now question the accuracy of the stovetop thermometer. I will be checking it against my IR when I find it.
 

begreen

Mooderator
Staff member
Nov 18, 2005
79,592
South Puget Sound, WA
560º is not too hot for the stovetop. Our Castine operated regularly in the 650-700º range during cold weather. Good idea to check the accuracy of the thermometer with the IR.
 

webby3650

Master of Fire
Sep 2, 2008
10,521
Indiana
That certainly doesn’t sound like a panic situation. The oval will run way hotter than the corner where the thermometer goes. What temps are you used to seeing?
 
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Highbeam

Minister of Fire
Dec 28, 2006
16,474
Mt. Rainier Foothills, WA
When you’re unable to cool things down, they always seem to be super hot and running away! Plus your adrenaline and heart rate.
 

Sodbuster

Minister of Fire
Sep 22, 2012
1,191
Michigan
I know the smell, and I can relate to the heat, but these stoves are harder to break than you think. I've seen welds (not in a stove) glow to bright red, and be fine.
 

Stinkpickle

Feeling the Heat
Jan 13, 2015
375
Iowa
With the short legs and tight clearance to the firebrick I’m not sure I could even reach my air intake when the stove is roaring hot. I’ve considered practicing on a cold stove to see if it’s even possible. Probably should.
Yeah, I don’t think I would be comfortable without a way to completely choke it off in such a situation.
 

webby3650

Master of Fire
Sep 2, 2008
10,521
Indiana
When you’re unable to cool things down, they always seem to be super hot and running away! Plus your adrenaline and heart rate.
If it were in fact too hot, then ya. It’s always best to be overly cautious, if things are installed properly though, it will be fine. I’ve had it happen, it can be scary.
 

Sawset

Minister of Fire
Feb 14, 2015
624
Palmyra, WI
What I used to see were not so much stove top temps getting out of hand, but the flue temps. In real cold weather, it's not uncommon at all to have stove tops 500-650. Maybe a little higher, a little. The problem comes in, at least here, is when the fire box is hot, putting out lots of well needed heat, then adding some dry fuel, that would immediately offgas and create more heat. More heat may be good, unless the stack temps are already high to begin with, which they were. They go higher, and shortly too high. It's not so much running away, but more the the temp is cycling up, and in this case, too far up. I used a welders mitt to cut the air in back, and down would come the flue temp. Over time, I realized that allowing the stove to run down a little, 400f is that point, where any of those flue temp rise issues remained well within range. It happened a couple times the first few years, none since.
threelittlefish, do you not have a flue thermometer?