Stove overburn

[brownie]

I have a friend who is new to wood burning. He was told to burn his stove at 500 to 600 that is alot higher than I burn 300 to 400.
He was also told to burn at 1000 for 2 hours to keep the chimney clean. My stove heats very well at 300 and no build up in the chimney. I am afraid he will burn out his stove or his house.

 

[MountainStoveGuy]

What brand/kind of stove is it? different stove materials will have different operating temp's. Who gave him/her this info?

 

[brownie]

I don't know the brand ,but it is steel plate and it was the dealer that told him.

 

[MountainStoveGuy]

Steel surface temps can be alot higher then cast, and substantially higher then stone. I personaly would never recommend a 1000 degree burn, but its the manfucaturs responsibility to provide burn rates. If the dealer is telling the customer different then the manual of the stove, i would follow the stoves recomendaations. You can achieve different flue temps with different stoves. Older ineficient stoves can have very high flue temps, and newer one can have relativly low temps. Hope that helps.
RYan

 

[Corie]

1000 for 2 hours to keep the chimney clean

That is VERY VERY risky. The idea that the stove is at 1000 degrees is frightening since it is a fact that creosote ignites at a 650 degree stack temperature.

Besides the fact that thermal cycling results in high stresses along places like welds and holes/openings. Over time, repeating thermal cycling will significantly decrease the life of the stove.

 

[precaud]

There's alot of unnecessary fearmongering about burning stoves hot, probably by folks who have never done it. I still have a Jotul 602 which I used for 15 years. With only softwoods to burn, I really had no choice but to burn it hot... Almost every load would bury the thermometer on the top plate above it's 900F upper limit. It's still in excellent condition, with no warps or cracks or any other defects.

 

[Corie]

Along those lines though, just because you burned a stove that hot for all those years does not mean it is a safe or correct practice. When stoves are engineered, the materials they are designed with are chosen specifically for the thermal range and the amount of stress they will see. Operating way out of that thermal range can result in phase change in both cast iron and steels. Granted, the phase change happens at temperatures slightly higher than those being discussed here, nonetheless it might be a concern.

Also, thermal expansion can result in higher than expected stress concentrations in certain areas of the stove. It would be nice to think that all wood stoves are designed with a factor of safety high enough to allow such overburning, however that may not be the case, and I don't think a box of burning fuel is a time to test the competence of the engineers who designed the stove.

 

[wahoowad]

precaud, how did you burn so hot? I assume you ran it wide open, yet that doesn't seem like an efficient use of wood (it would burn it up in an hour or two)

 

[precaud]

precaud, how did you burn so hot? I assume you ran it wide open

No, I would never do that. That invites overfiring, for sure. The air control was open 3/8 to 1/2 inch during operation.

yet that doesn't seem like an efficient use of wood (it would burn it up in an hour or two)

Burning ponderosa and pinon pine, you're looking at about 75-90 minutes per load in a 602. I have a new F602 also, and the old one is more efficient than the new one, no question. And, when burned hot, almost burns as clean too.

 

[begreen]

An hour or two burn is pretty normal for a 602 with softwood. But I used ours for 10 yrs with softwood and never ran it at those temps. That's maybe because I put in a draft damper, which helped a lot in controlling the burn and putting out more heat over longer burns. My normal stack temp at 18in. above the stove was about 600 deg. We didn't have the thermometer on the stove top because there was a decorative, Jotul top on it.

Hey Wahoo, how has the 3CB been doing?

 

[begreen]

I have a new F602 also, and the old one is more efficient than the new one, no question. And, when burned hot, almost burns as clean too.

Interesting. I always thought that the older 602 was a very efficient stove based on the heat output and wood consumption. My chimney stayed incredibly clean inspite of burning fir, alder and hemlock. The trick seemed to be keeping all the baffles and plates in good condition. I also did a modification by adding a back, interior baffle that helped prevent overheating the back of the stove (notorious source of cracks in the backs of 602s). How is the new stove differing wrt efficiency?

 

[precaud]

Corie, you're making an awful lot of assumptions here...

Along those lines though, just because you burned a stove that hot for all those years does not mean it is a safe or correct practice.

In the hands of a conscientious operator, I think it is perfectly safe. AND correct, in terms of efficiency and clean-burning.

When stoves are engineered, the materials they are designed with are chosen specifically for the thermal range and the amount of stress they will see. Operating way out of that thermal range can result in phase change in both cast iron and steels.

A nice general statement, but obviously I was not "operating way out of that thermal range".

Granted, the phase change happens at temperatures slightly higher than those being discussed here, nonetheless it might be a concern.

Quite a bit higher, I'd say.

Also, thermal expansion can result in higher than expected stress concentrations in certain areas of the stove. It would be nice to think that all wood stoves are designed with a factor of safety high enough to allow such overburning, however that may not be the case, and I don't think a box of burning fuel is a time to test the competence of the engineers who designed the stove.

You make it sound like I am advocating that everyone burn their stove as hot as possible, at the bleeding edge. Not at all. If you pay attention, stoves will tell you how they like to be burned. With each stove I've ever had, EPA or pre-EPA, I looked for the "sweet spot", the best combination of heat output, burn time, and clean combustion, and adjusted my habits accordingly. Every stove seems to have such a sweet spot. The old 602's was as I described. The new F602 is lower, about 700F. My Morso 2110 is totally different. It's sweet spot is about 550-650F (on the top plate). But that's because of it's design and construction is different. The hottest surface on the Morso is not the top but the front (i.e. the glass). ALOT of it's heat is radiated through the glass - I'm sitting 15 feet away from it and I can feel it!

 

[precaud]

Interesting. I always thought that the older 602 was a very efficient stove based on the heat output and wood consumption. My chimney stayed incredibly clean inspite of burning fir, alder and hemlock.

Yep, it's a real gem, for sure...!

I also did a modification by adding a back, interior baffle that helped prevent overheating the back of the stove (notorious source of cracks in the backs of 602s).

Interesting. I never had any problems with the back. I did some mods on mine also, blocked off some of the top air holes and added an extension to the baffle at the front to force things to mix before it left the firebox. It definitely burned cleaner and hotter after that...

How is the new stove differing wrt efficiency?

It's still a joy to use, but for the same amount of wood in, it puts out less heat. It's 40 pounds heavier and completely lined on all sides, so it contains alot of the heat in the firebox. Still a very nice stove, but doesn't have the "wow" factor that the old 602 does...

How would you compare your F3CB to your old 602, efficiency and heat-wise?

 

[Corie]

Eutectoid temperature for steel is 740 degrees C. That is 1364 degress F. If you want to discuss burning at 1000 degrees, i don't consider 1300 to be that much higher. When I'm referring to phase change I don't mean the point at which solid steel turns molten. I'm referring to the point at which the various compounds that make up carbon steel begin to change.

Also, I'm not trying to make it sound like you advocate everyone burning their stove extremely hot. In fact, I'm REALLY not trying to start an argument with you at all. I just don't agree with the wording "unnecessary fearmongering" in reference to heating a stove to above 1000 degrees F. If that was the place at which you believe your stove operated most efficiently, maybe it was.

I do feel though, that burning a stove that hot is a safety hazard, unless the operator is present and watching the stove. But that's me. I wouldn't walk out of the house for work in the morning with the stove running at a 1000 degree surface temperature. Nor do I think anyone should. Maybe you didn't leave the fire unattended when burning that hot? Maybe you kept your chimney extremely clean at all times.

There are a lot of variables in burning a woodstove and there are even more when operating at temperatures that high. You and I don't know the condition of this person's chimney, or the way they operate the stove. So to call worrying about stove temps "unnecessary fearmongering" could be very dangerous.

I don't mean to come off as a smart ass or argumentative, but I think we should be more careful when we suggest things like that. That's all.



And, directly from the current Jotul 602 manual (I know you had an older stove)

With intense overfiring, temperatures on the surface of the Jøtul F 602 USA can exceed 1 000 F (536 0C).

 

[begreen]

I think you said it right with the 'wow' factor in the old 602. People would come in and be startled that we were heating the whole house with that one little stove. The 3CB is definitely more uptown and has major wife approval. It's nice to see the source of one's heat and the cool secondary burning. We like being able to squeak in longer logs, though the firebox capacity is only about twice that of the 602. Heatwise the 3CB can't quite provide the almost instant warmth of the 602, it takes about 30 minutes to warm up all that cast iron. But once it gets cooking, it can put out as much heat as the 602, if not a bit more. Our burn times are now more like 2-4 hrs., though I have managed to have a warm stove with glowing coals, once or twice 6 hrs. later. In all honesty, if I did it again, I probably would have gone for the Castine, but we were a little tight on side clearances and I got a good deal on the 3CB.

 

[precaud]

I don't want to argue, either. Nor do I want novice users to get uneasy when they see their stove 'stat go above 600F, as I've read several times on different forums. Chances are it's operating just fine.

I don't burn when I'm not at home, so I rarely leave fires unattended. And again, there's nothing to be afraid of when it's operated at it's effiency point. It's quite stable - it wants to burn there!

Also, there's no need to exagerate to make your point... I said 900F, not 1000F... peace.

 

[DavidV]

I have a question about the inital Post. Brownie is it a cat stove, and if so is this a surface or probe tempurature. Because the instructions that came with my stove(17 year old stove) say to burn it at 600 degrees before engaging the cat. I have newer more efficient cats so I engage at 400. And thank god for that becuase I use front surface temp. I don't have a probe thermometer. I imagine my temps in the CAT probe area are way higher than my surface temps. It isn't uncommon for my thermometer to read 500-550. Sometimes hitting 600. 650 is very unusual and if it starts climbing past that, I tend to damp it down.

 

[precaud]

But once it gets cooking, it can put out as much heat as the 602, if not a bit more.

Interesting. I was wondering why my Jotul dealer steered me away from the F3... they said it wouldn't put out much more heat than the 602, and I thought they were pulling my leg. Apparently not...

In all honesty, if I did it again, I probably would have gone for the Castine, but we were a little tight on side clearances and I got a good deal on the 3CB.

Take alook at the Morsos if you decide to upgrade. I've been a Jotul user for decades and am very impressed with my 2110. Jotuls are cast in Norway but are now assembled in the USA and I think the quality control has gone downhill... my F602 was awful. The entire back plate was loose and the baffle misaligned with huge gaps.

 

[precaud]

My normal stack temp at 18in. above the stove was about 600 deg.

Well if your stack temp was running 600F, the stove top would have easily been several hundred degrees higher... so I think our running conditions were pretty much the same.

 

[Martin Strand III]

Hi Squabblers:

Longstanding rules of thumb for maximum burning temperatures of your stove are:

1. Follow your mfg instructions for your specific stove

2. Burning hot enough to make the metal glow red (about 900* F for cast iron or steel) near the top plate/flue is a sign of over-firing which, if continued long enough, will damage your stove and perhaps your home

Wanting to burn hot to burn clean is good. Burning too hot in a metal stove is not good. The problem is inherent in your metal stove. It is not designed for prolonged burns at 1100* F required to get all the BTU's out of that smoke, thus less creosote, yada. Some cats come close by burning the smoke at lower temps but require maintenance and fussin' so they're not my billy-whack.


Aye,
Marty

Grandma used to say, "Seeing metal red could make you dead."

 

[begreen]

My normal stack temp at 18in. above the stove was about 600 deg.

Well if your stack temp was running 600F, the stove top would have easily been several hundred degrees higher... so I think our running conditions were pretty much the same.

You know, I never did a cross check on the 602 to compare stack surface to stove top temps. However, with the 3CB, the two temps are very close, usually with 25-50 deg., but nothing like 300 degrees apart. Give it a try on your stove, I'd be curious to hear what you find out.

 

[precaud]

However, with the 3CB, the two temps are very close, usually with 25-50 deg., but nothing like 300 degrees apart.

Hmmm... I'm surprised by that. For the exhaust to travel that far and lose that little heat doesn't make sense to me.

Give it a try on your stove, I'd be curious to hear what you find out.

Unfortunately I can't access the flue on the Morso - it totally blocks the fireplace opening. But I will have the F602 up and burning in a couple weeks so I'll try it on that one and let you know.