Still having problems with Jotul Oslo

[Nonprophet]

In this thread, I mentioned some problems I was having with our new/used Oslo, primarily that the stove seems starved for air. So, taking advice from forum members I totally re-did our chimney, going from 8" single wall pipe (outside too!) to 6" double wall/class A pipe. Needless to say, it was not cheap!

The first fire we lit after re-doing the chimney burned well, but it was only 28 that night so I expected it to do well. Here in our part of Oregon, we have fairly mild winters, I'd say our overnight lows average between 28-36. The past couple of nights have been more typical, overnight lows of 34, 36, and 38 last night. The bottom line is that while there has been some improvement, I still don't think our Oslo is performing very well.

For example, last night it was 36. I started a fire with very dry 2x4 lumber scraps. Even once they were burning well, I have to keep either the front or the side door cracked for at least 15-20 mins or else the fire will go out. I got a decent bed of coals going, then added several smaller splits of VERY dry Doug Fir (12-14%) and really got the fire going adding more split over a 30 min period. Basically, I was trying to get the stove as hot as I could as fast as I could. After another 35-40 mins (doors shut air wide open) the firebox was raging! Still, I was only able to get the stove top corners up to 600--it just won't get hotter than that. The center griddle was 650-675, but the corners hovered around 600. I brought the air down to 1/2 and the secondaries kicked in just fine, and I was gradually able to get the air down to 1/3 or so--any lower and the secondaries would peter out.

The Oslo put out a good amount of heat and within 90 mins or so the Yurt was up to 72 inside with 36 outside--not bad. Still, I can't understand why it won't get hotter. Our Defiant/Encore (using the old 8" single wall flue) would often-times try to get away from us--easily reaching 750-800 degree stove top temps! Again, the wood isn't the problem, I'm ONLY burning 2 year old very dry Fir or 3 year old very dry Cherry.

Just for the heck of it, I went ahead and drilled a few more holes into the "inspection plate" cover (some people call it the doghouse) to try and let some more air in. It's been pretty warm today so I haven't built a rager, but one noticed improvement is that starting the fire I can put in paper and kindling and actually shut the door within 5 mins and not have the fire go out--a nice improvement, but I'm not sure what, if any effect it will on stove-top temps once I'm really trying to crank it. I think my draft is fine, i.e. no back-puffing, no smoke entering the room, etc., but still the stove seems starved for air.

To clarify, here is our new flue/chimney set up: 6" double wall black 45 from flue collar to 24" of double wall black stove pipe to another dw 45, through an 18" section of 6" class a (horizontal/thimble) into a class a 6" "T", then straight up with 12' of class a 6", then 4' of 6" single wall (wanted to test extra height before spending more money on class a pipe!!) then china hat. That gives me 19' of chimney---should be more than enough............

Any ideas???


NP

 

[Shari]

The ideal heat range for the Oslo is 400-600 so I would say you are right where you should be. Any higher than 650 I believe is considered 'over fire' for the Oslo.

Shari

 

[fbelec]

don't know anything about jotul's but 600 or 650 sounds ok. you can't be comparing it to the vermont castings. every stove has different running temps. 650 or higher on my hearthstone 2 would be overfiring it according to the heathstone wood tech. how long does it burn for you when your running at 600 or 650? is it keeping the house warm? check your thermometer put it in your oven set at 400 and see if it matches

 

[Nonprophet]

The ideal heat range for the Oslo is 400-600 so I would say you are right where you should be. Any higher than 650 I believe is considered 'over fire' for the Oslo.

Shari

Well, that's good to know! I've been reading through numerous Oslo threads here and it would seem that most people can get up to 500-600 and start turning the air down and still maintain 550 or so pretty easily. The best fire I've had so far I got the stove top up to 600, and started backing down the air--the secondaries were firing right away. I usually start by backing the air down to 1/2 and that will maintain the secondaries just fine, but anything below 1/3 air (unless the firebox is just jam-packed) will just smolder with no secondaries. It seems from reading other Oslo threads that most people are able to maintain the secondaries with 1/4 or even less air, is that a correct observation?

Thanks!


NP

 

[Nonprophet]

don't know anything about jotul's but 600 or 650 sounds ok. you can't be comparing it to the vermont castings. every stove has different running temps. 650 or higher on my hearthstone 2 would be overfiring it according to the heathstone wood tech. how long does it burn for you when your running at 600 or 650? is it keeping the house warm? check your thermometer put it in your oven set at 400 and see if it matches

Yeah, thermometers check out using my IR, so I think the readings are pretty accurate.

Once I turn down the primary air to 50% or so it will hold at 500-525 on about a 1/3 load for about 3 hours before needing more wood--this is 3 year old Cherry I'm putting in there. Most of my wood is cut at 16" or larger, and the Oslo needs 14" pieces for a N/S burn, so I've been doing E/W burns. The longest burn I've gotten so far was about 6 hours loaded about 3/4 full with enough coals to start up again in the morning. One thing I really like about the Oslo is that it holds heat for a loooooooong time--i.e. if I let the fire go out in the AM it will still have a 90 degree surface temp 4-6 hours later.


NP

 

[fbelec]

other than your air control only down to half it sounds like it's running fine. 6 hours on 3/4 load is good.

 

[SWNH]

I started a fire with very dry 2x4 lumber scraps. Even once they were burning well, I have to keep either the front or the side door cracked for at least 15-20 mins or else the fire will go out. I got a decent bed of coals going, then added several smaller splits of VERY dry Doug Fir (12-14%) and really got the fire going adding more split over a 30 min period. Basically, I was trying to get the stove as hot as I could as fast as I could. After another 35-40 mins (doors shut air wide open) the firebox was raging! Still, I was only able to get the stove top corners up to 600--it just won't get hotter than that. The center griddle was 650-675, but the corners hovered around 600. I brought the air down to 1/2 and the secondaries kicked in just fine, and I was gradually able to get the air down to 1/3 or so--any lower the secondaries would peter out.

Been there, done that...still do that. In this weather (mid 30s), it take me an hour to get things going well enough to leave it alone. I rarely get the stove top to 600 (only once got to 650). Mostly around 500...plenty to warm the house even on the coldest days.

I like the idea of more holes in the air cover. I plan to do the same. It should only affect things when the lever is wide open.

 

[begreen]

So what's the "problem". Sounds like this is a great improvement from the previous reports.

 

[Rob From Wisconsin]

Wow, people are spoiled.....

I would have been happy to have been able to maintain my Oslo
at 450 degrees, but that became rare.

Sounds like you have no problem at all.....

 

[logger]

Wow, people are spoiled.....
I would have been happy to have been able to maintain my Oslo
at 450 degrees, but that became rare.
....

What the heck was the problem with your stove/wood? My Oslo stays around 450-550 when in use. I can get it up to 700 if need be, but only did that once. Getting the stove to 600 shouldnt be a problem. If it is, something is wrong. I burn all sorts of wood and one thing about cherry is that although it burns pretty good, its tough to get the stove really hot with it. I'd buy a few bags of store wood and fill her up just to make sure its not the stove at fault. If it still wont get past 550, theres definately a problem that needs to be fixed.

 

[Fsappo]

Your stove is working fine

 

[firefighterjake]

Seeing no problem here . . . the Oslo secondaries should kick in once you get the stove top temp at 450-550 . . . I wouldn't recommend going over 650 degrees stove top temp. You're getting heat, long burn and secondaries . . . other than the fact you're not able to shut down the air control to a quarter mark (and some folks may not be able to do so due to the climate, stove set up, etc.) it seems as though there are no real issues here.

I should mention that when I start up from a cold stove the first fire generally doesn't seem to really pump out the heat or get going quite so quickly . . . where I tend to notice the heat more is when I reload the stove after getting it going . . . for some reason (maybe because there is more room for wood vs. kindling) the reload seems hotter and seems to take off quicker.

 

[Rob From Wisconsin]

Wow, people are spoiled.....
I would have been happy to have been able to maintain my Oslo
at 450 degrees, but that became rare.
....

What the heck was the problem with your stove/wood? My Oslo stays around 450-550 when in use. I can get it up to 700 if need be, but only did that once. Getting the stove to 600 shouldnt be a problem. If it is, something is wrong. I burn all sorts of wood and one thing about cherry is that although it burns pretty good, its tough to get the stove really hot with it. I'd buy a few bags of store wood and fill her up just to make sure its not the stove at fault. If it still wont get past 550, theres definately a problem that needs to be fixed.

I wasn't totally sure, but we ended-up selling it & replacing it with a generic steel-box stove.
The cheap replacement stove ended-up out performing the Oslo.
I eventually ran-into the person I sold my Oslo to & he voice similar problems.
I felt bad for him, because he really depended on wood heat.
We have since moved to a different house & purchased another stove.

 

[logger]

The cheap replacement stove ended-up out performing the Oslo.
I eventually ran-into the person I sold my Oslo to & he voice similar problems.

Then there was something wrong with that particular stove. I've ran numerous stoves and our Oslo is by far the most enjoyable and effective stove I've burned.

 

[CarbonNeutral]

Mine ticks on nicely at 400, got it to 630ish before, can get it to 500 with a good load of dry wood no problem at all. It heats the house nicely, even in the 400 range (450 in the center)

 

[Battenkiller]

I burn all sorts of wood and one thing about cherry is that although it burns pretty good, its tough to get the stove really hot with it. I'd buy a few bags of store wood and fill her up just to make sure its not the stove at fault.

Funny, I just started my stove (basically a cold start) with way less than 20 pounds of cherry and it got all the way to 750ºF on the center of my griddle top in about 20 minutes, and that's with shutting the air down halfway after about 5 minutes. Had to leave the room it was so hot, which is why I'm online instead of working down there. In my experience, well-dried cherry is a hot and intense (albeit somewhat short-lived) heat source. I always start my stove with cherry to get it hot real fast, then throw on the ash and hickory to get it to last all day.

Just curious.... Why would store-bought wood be better than his 3 year-old cherry? For starters, the store-bought wood could be anything, maybe even cherry... or worse (right down to poplar). And don't count on it being any drier than what comes out of a covered 2-3 year-old outside stack. Kiln-dried firewood doesn't stay kiln-dry for long (if it ever really got there in the first place). It quite quickly reaches equilibrium with the ambient relative humidity of the storage facility. I can't imagine anyone warehousing kiln-dried wood in a heated spaced just to keep it "kiln-dry". Within a very short time in an unheated warehouse, it is back up to 12-15% MC, same as naturally seasoned wood. Same thing happens with furniture grade wood, which is why experienced woodworkers always bring their wood out of storage and into the heated shop a few weeks before starting a new project.



Anyway, if I bought a stove and 400º was considered cruising, I'd get another stove. Physics will tell you that a stove like the Oslo, with about 20 sq.ft. of surface area, will only put out about 25,000 BTU if every square inch of the thing - including the bottom - are at 400ºF. That's about 1/3 of its rated maximum. If it was all at 600º, it would be putting out about 57,000 BTU. Of course, stoves are never that hot all over, so total heat output is even less.

I wonder how hot Jotul would have to get an Oslo to get it to put out its supposed max rated 70,000 BTU? It'd have to be in the range they consider to be "overfire" for sure.

 

[CarbonNeutral]

Anyway, if I bought a stove and 400º was considered cruising, I'd get another stove. Physics will tell you that a stove like the Oslo, with about 20 sq.ft. of surface area, will only put out about 25,000 BTU if every square inch of the thing - including the bottom - are at 400ºF. That's about 1/3 of its rated maximum. If it was all at 600º, it would be putting out about 57,000 BTU. Of course, stoves are never that hot all over, so total heat output is even less.

I wonder how hot Jotul would have to get an Oslo to get it to put out its supposed max rated 70,000 BTU? It'd have to be in the range they consider to be "overfire" for sure.

Not saying you're wrong, but what calculation did you do to get these values. Equally, while of course manufacturers' specs are to be taken with a pinch of salt, I'd be surprised if they went as far to use an overfire temperature to provide their BTU rating. Just measured the Oslo - you're about right on the sq ft - I calculated 21.5 sq ft based on flat surfaces. Given the patterns and shapes, I would guess that it's more like 25 sq ft.

 

[oldspark]

I burn all sorts of wood and one thing about cherry is that although it burns pretty good, its tough to get the stove really hot with it. I'd buy a few bags of store wood and fill her up just to make sure its not the stove at fault.

Funny, I just started my stove (basically a cold start) with way less than 20 pounds of cherry and it got all the way to 750ºF on the center of my griddle top in about 20 minutes, and that's with shutting the air down halfway after about 5 minutes. Had to leave the room it was so hot, which is why I'm online instead of working down there. In my experience, well-dried cherry is a hot and intense (albeit somewhat short-lived) heat source. I always start my stove with cherry to get it hot real fast, then throw on the ash and hickory to get it to last all day.

Just curious.... Why would store-bought wood be better than his 3 year-old cherry? For starters, the store-bought wood could be anything, maybe even cherry... or worse (right down to poplar). And don't count on it being any drier than what comes out of a covered 2-3 year-old outside stack. Kiln-dried firewood doesn't stay kiln-dry for long (if it ever really got there in the first place). It quite quickly reaches equilibrium with the ambient relative humidity of the storage facility. I can't imagine anyone warehousing kiln-dried wood in a heated spaced just to keep it "kiln-dry". Within a very short time in an unheated warehouse, it is back up to 12-15% MC, same as naturally seasoned wood. Same thing happens with furniture grade wood, which is why experienced woodworkers always bring their wood out of storage and into the heated shop a few weeks before starting a new project.



Anyway, if I bought a stove and 400º was considered cruising, I'd get another stove. Physics will tell you that a stove like the Oslo, with about 20 sq.ft. of surface area, will only put out about 25,000 BTU if every square inch of the thing - including the bottom - are at 400ºF. That's about 1/3 of its rated maximum. If it was all at 600º, it would be putting out about 57,000 BTU. Of course, stoves are never that hot all over, so total heat output is even less.

I wonder how hot Jotul would have to get an Oslo to get it to put out its supposed max rated 70,000 BTU? It'd have to be in the range they consider to be "overfire" for sure.

I read in another post about the moisture in the wood reaching equilibrium withe the ambient relative humidity of the building, please explain this to me as it seems like you are saying the moisture content of the wood will be the same as the surrounding air and I do not think that is the case but not sure if that is what you are saying.

 

[CarbonNeutral]

A post I found here (you do believe everything on the internet don't you?): http://nepacrossroads.com/about15468.html

has this table:

Temperature of Surface Fahrenheit -------------- Total Energy Transferred BTU's per hour per foot

80* ------------------------------------------------------ 15 Btu's / Sq.Ft.
100* ------------------------------------------------------ 51 Btu's / Sq.Ft.
150* ------------------------------------------------------ 168 Btu's / Sq.Ft.
200* ------------------------------------------------------ 315 Btu's / Sq.Ft.
400* ------------------------------------------------------ 1230 Btu's / Sq.Ft.
600* ------------------------------------------------------ 2850 Btu's / Sq.Ft.
800* ------------------------------------------------------ 5430 Btu's / Sq.Ft.
1200* ----------------------------------------------------- 9370 Btu's / Sq.Ft.

So 25sq feet puts out 30,000 BTUs per hour at 400F, while 600 puts out 71,000 BTUs, not in the overfire range for the Oslo, assuming the table is at all accurate.

Addendum: There certainly is something odd with that data - can't believe there's that double inflection in the line.

 

[BrotherBart]

I should mention that when I start up from a cold stove the first fire generally doesn't seem to really pump out the heat or get going quite so quickly . . . where I tend to notice the heat more is when I reload the stove after getting it going . . . for some reason (maybe because there is more room for wood vs. kindling) the reload seems hotter and seems to take off quicker.

That is because the stove top heats up faster than the rest of the stove body Jake. By the time you reload the stove body temp has come up to close or the same as the top so you have more iron radiating heat. And the firebox temp has stabilized so the new wood takes off faster.

 

[Dakotas Dad]

Interesting bit of heat data.. the biggest thing I see is that at least on my stove, the temps are far from even over the surface of the stove. When my top center stone is cruising at 400-450, my side lower stones are running about 500+, I don't know what the back is doing, because of the heat shield and blower, but it's pretty warm. I may try to get a probe against it with the blower off this evening, if we get the stove that hot. Interestingly, for all the hearth ratings required, the bottom really doesn't give off much heat.

Another thought is that it's all a bit relative when talking stove surface temps, since different brands/types/styles all vary so much. I see so many people on here talking about getting their stoves way hot.. and I know my stove manual says 600 MAX. I think, if the thing heats your space to satisfaction, doesn't smoke or dirty the glass.. your good. Think of the millions of people who heat or have heated their homes for eons, never knowing for a moment any more about stove or flue temp then "man that's hot".

 

[begreen]

Hearthstone soapstone stoves have a lower temp limit than cast or steel stoves. The recommended operating range for the Oslo is 400-600, but it can run at 700 if you need it to without worry of overfire.

I remember having this problem when I first ran the Castine and thought something was wrong with the stove. Then temps dropped, draft and my techniques improved and hitting 650 became pretty easy. There's a learning curve with every stove. They don't drive like grandpa's Ford truck. It takes awhile to get the most out of it.

 

[CarbonNeutral]

They don't drive like grandpa's Ford truck.

And nor do they do 10 gallons per mile, but I guess that was your implication

 

[Battenkiller]

So 25sq feet puts out 30,000 BTUs per hour at 400F, while 600 puts out 71,000 BTUs, not in the overfire range for the Oslo, assuming the table is at all accurate.

Addendum: There certainly is something odd with that data - can't believe there's that double inflection in the line.

Below is the table I used in my estimate. There appears to be an error in your table at 1200ºF. That should be the output at 1000º, with 15,100 BTU at 1200º. If you redo the graph with the figures from my table you should get a more evenly concave shape to the graph. And please do, since I think graphs are the very best way to communicate these points.

Note that the table is for total heat output, not just radiant heat. You can also see that the ratio between convected and radiated heat is not constant over this temperature range, and this will affect the shape of the graph as well, although it should remain concave throughout.

Whatever the total radiating surface of the Oslo truly is, there is no way that the bottom, for example, is contributing much to the heat output of the stove. I used measurements from the Jotul website, so I got close enough to make the point I'm trying to make. My VC Vigilant is pretty close to the same size as the Oslo, but is only rated at 50,000 BTU. I think this is a much more realistic estimate of output from either stove. The old Defiants were rated at 60,000 BTU, and I do believe a Defiant would absolutely smoke ('scuse the pun) a 70,000 BTU Oslo in a side-by-side heat output test.

My IR thermometer has a scanning function that allows me to take an average temp over a large area. Naturally, I just had to play with this function. By playing the laser dot over each plate (except for the bottom and the back, which is inaccessible to my IR gun), I was able to estimate total output at various temps and during different burns. Spot readings jump all over the place depending upon how big the internal hot and cool spots are, but the average of the top plate is always lower than the center where I place my thermometer by a big percentage. Side plates are rarely as warm as the top, front plate and doors can be the hottest parts of the stove well into a good burn, but rarely average much over 600ºF no matter how hot the stove top gets (and I'm talking 800º at times). So I strongly feel that to get a Jotul Oslo to put out 70,000 BTU, some parts of the stove would have to be well above 650º. I've hit 1047ºF on one spot on my left door, enough to make it glow in a darkened room, but the whole plate only averaged about 650º. Just how evenly can the Oslo heat up by comparison? Only your IR gun knows for sure. ;-)

I read in another post about the moisture in the wood reaching equilibrium withe the ambient relative humidity of the building, please explain this to me as it seems like you are saying the moisture content of the wood will be the same as the surrounding air and I do not think that is the case but not sure if that is what you are saying.

.

Actually, the moisture content of the wood will always be tons higher than the surrounding air. Air, being a gas, just can't hold all that much moisture. Even at 100% relative humidity, there are only grains of water in a given volume of air compared to at least a pound in a big split of wood at 15% MC.

Below is a chart that will tell you what moisture content your wood will equilibrate at over a range of relative humidities from 0% to 100% RH. Find the average seasonal RH in your area and that will tell you the MC of your wood. Even after a couple of centuries, wood still obeys these basic rules. I work on violins that are over 300 years old. Even after all that time, they will swell and warp severely in a tropical (very humid) environment, or shrink dramatically and crack if I let them get too dry in my shop.

 

[CarbonNeutral]

Your point about the bottom of the stove is absolutely correct. Maybe I would balance that though with the increase in radiant heat through the glass, maybe not. Below is the chart redone with your table - much nicer curve to it. At the end of the day, my stove running at 400-450 heats the appropriate parts of my house (i.e. not all of it) through a NE winter with next to no back up from the oil boiler.

Edit: I think the white enamel gives it extra magic powers, doubling the BTUs with half the wood