Cast Iron and cracking

[Bill]

Someone just mentioned this to me that if a cast iron stove is lets say 0* and you start a fire in it, you have to be careful not to heat it to fast or it will crack. Is this true?

 

[elkimmeg]

Rapid heating or expansion will crack many materials including cast iron I think you would have a better chance cracking it with a sledge hammer

 

[babalu87]

I havent cracked a cast iron pan yet and I have taken that HOT off the stove and put cold water in it.
Maybe with a firebox full of Napalm but exactly what situation would occur for a stove in a house to attain a temperature of ZERO degrees?

I like the hypothetical angle as much as anyone but that is beyond the pale

 

[Harley]

I think for all practical purposes... it's not likely to happen. If your stove is at 0* and you go to start a fire (assuming using normal kindling or sirestarters) - the stove is going to heat up pretty slowly. The bigger risk is probably going in the other direction.... say you have a 5-600* stove and drop a cold pan of water on it.... you might have a problem there.

 

[Bill]

Thanks for your replys, but my cabin is below freezing all winter until I start a fire. We do not keep it heated while not there, and in theory it could get below zero, depending on the weather. Just a concern thinking about a stove replacement.

 

[webbie]

Consider a car engine and exhaust manifolds that go from cold to red hot very often - they don't crack. It would take a lot of shock to hurt a good cast iron stove.

 

[restorer]

Cast iron absorbs a tremendous amount of heat before it starts to dramatically expand. In theory, if you took a piece of cast iron and instantly raised it to 1,500 degrees F. it might crack, but the stove will really raise the temperature gradually. Most cracking in cast iron comes from extreme overheating, such as engine blocks or heads without cooling liquid. Or heating and striking cast when in the red stage or higher. I have seen cast iron heated in a forge to a bright cherry and welded with proper cooling it is as good as new. Rapid cooling can do more damage than rapid heating. A stove in a very cold cabin with a normal fire start should not be a problem, just anticipate a little longer time to heat the air than normal.

 

[wg_bent]

For that use, the steel stove will heat up faster and produce usable heat quicker...although I have no idea how much faster. Need input from someone who has owned both.

 

[begreen]

Now if this is with a cheaply cast Vogelzang or Scandia stove in the backwoods cabin, then maybe?

 

[Gooserider]

I can see the coming into an unheated cabin scenario, but I don't think it's likely to be a problem unless your normal fire-building technique involves the kinds of incendiary devices that are likely to get the BATF on your case... :gulp: (or maybe those charcoal lighting BBQ guys from NASA - 15 seconds from cold to "cooking ready" at a serious cost in pyrotechnics...)

Normally if you go to light a fire, you will be doing the gradual newspaper -> kindling -> small splits -> big stuff sequence (or some variation) that, by it's very nature, starts with a small fire and grows in flame size and heat - this will minimize the thermal shock to the cast iron, even granting that it was a problem in the first place - which I kind of doubt.

I also have serious doubts that there would be a noticeable difference in how long it took to get heat out of a cast-iron box compared to the same size steel box - no more than a minute or two if that. Of course, as mentioned earlier, this does assume a decent quality stove, not one of those cheap jobs you couldn't trust to hold together under any conditions...

Gooserider

 

[webbie]

For that use, the steel stove will heat up faster and produce usable heat quicker...although I have no idea how much faster. Need input from someone who has owned both.

I don't think this is true. Steel and cast iron are the same element and the heat transfer through two identical thicknesses is likely to be similar.

That said, specific stove design comes into play. A stove lined with thick firebrick, a cat stove or a stove like VC with a lot of extra chambers (some refractory lined) will take longer to heat up than a basic non-cat.

 

[DriftWood]

Consider a car engine and exhaust manifolds that go from cold to red hot very often - they don't crack. It would take a lot of shock to hurt a good cast iron stove.

Cast iron is used in these manifolds. A well designed iron casting, manufactured right, instaled right, will last almost for ever. With a bad design , or badly manufactured, or badly installed, iron casting almost ever one will crack.

 

[Gooserider]

For that use, the steel stove will heat up faster and produce usable heat quicker...although I have no idea how much faster. Need input from someone who has owned both.

I don't think this is true. Steel and cast iron are the same element and the heat transfer through two identical thicknesses is likely to be similar.

That said, specific stove design comes into play. A stove lined with thick firebrick, a cat stove or a stove like VC with a lot of extra chambers (some refractory lined) will take longer to heat up than a basic non-cat.

This may be true in terms of getting up to "Optimal operating temps" but I still wonder how much significant difference is there in how long it takes to start getting significant heat out of the stove. IMHO this does NOT mean standing there with a stopwatch counting the milliseconds :long: the way Roo and Elk debate grams per hour :lol: I would say that any difference less than 5 minutes would count as "noise" and probably wouldn't consider a time difference of less than 10 minutes as a big issue.

Now the question is how would one determine "time to significant heat"? I would make a couple of gross assumptions -
1. That a stove which people want to get quick heat out of will have a blower
2. The blower will have a thermal switch on it
3. Since the Mfgrs know that quick heat up can be a sales advantage, they will setup the thermal switch to turn the blower on as soon as they feel the stove is able to put out useable heat.

Therefore I would consider the "time to significant heat" to be the time it takes to go from initially lighting the fire in a cold, dead stove, to the time when the blower first kicks in.

Now with my old smoke dragon, I can consistently do this in 7-10 minutes if I push it a bit. By my standards, I would consider any stove that could go from dead to blower on in under 20 minutes to be functionally equivalent, and a reasonably fast heating stove.

Just to compare notes, what sort of times do the rest of you get?

Gooserider

 

[begreen]

I can get the ecofan running in 15 minutes and get it to 200 degrees at about 20 min if I push it with the right wood. Pine kindling to oak flooring scraps would be what I'd be using to get her going quickly.

 

[BrotherBart]

3. Since the Mfgrs know that quick heat up can be a sales advantage, they will setup the thermal switch to turn the blower on as soon as they feel the stove is able to put out useable heat.

Therefore I would consider the "time to significant heat" to be the time it takes to go from initially lighting the fire in a cold, dead stove, to the time when the blower first kicks in.

EPA Method 28 requires that if a blower is standard or offered as an option that a full test run has to be done with the blower operated according the operating instructions. That would pretty much preclude stove companies from firing off that blower too soon in the burn cycle. They could watch twenty grand go down the toliet if they failed the emissions test by doing that and not letting the firebox heat up for reburn fast enough.

 

[Gooserider]

True, that helps keep them honest... Otherwise I'd tend to say it's somewhat beside the point - I don't care what is going on inside the firebox, I want to know when I'm getting enough heat on the OUTSIDE of the firebox to kick the blower on... If it's a smoke dragon like mine with a mostly bare metal box, with a snap switch on the vent outlet (I put it there) then you have a slight advantage. If you have 6" of firebrick, refractory and / or soapstone and other insulators to get through, then it's going to take longer - perhaps... FWIW, my stove doesn't do secondardy combustion (that I know of) but if it did, I don't think it would take much longer to get up to the appropriate temps - I get 7-10 minutes to the blower coming on, another 5 minutes to put the thermometer into the red zone, and maybe an additional five or less to get a nice cheery glow from the stovepipe - (No, it isn't a VC!)

From the other discussion I've seen, I'm guessing that I'm on the fast side with my stove, but not by that much, and there isn't that much of a spread between the plate and cast steel stoves in a given class. Soapstone seems to be enough slower to finish out of the class, but not by a huge amount.

Gooserider

 

[restorer]

For that use, the steel stove will heat up faster and produce usable heat quicker...although I have no idea how much faster. Need input from someone who has owned both.

I don't think this is true. Steel and cast iron are the same element and the heat transfer through two identical thicknesses is likely to be similar.

That said, specific stove design comes into play. A stove lined with thick firebrick, a cat stove or a stove like VC with a lot of extra chambers (some refractory lined) will take longer to heat up than a basic non-cat.

This may be true in terms of getting up to "Optimal operating temps" but I still wonder how much significant difference is there in how long it takes to start getting significant heat out of the stove. IMHO this does NOT mean standing there with a stopwatch counting the milliseconds :long: the way Roo and Elk debate grams per hour :lol: I would say that any difference less than 5 minutes would count as "noise" and probably wouldn't consider a time difference of less than 10 minutes as a big issue.

Now the question is how would one determine "time to significant heat"? I would make a couple of gross assumptions -
1. That a stove which people want to get quick heat out of will have a blower
2. The blower will have a thermal switch on it
3. Since the Mfgrs know that quick heat up can be a sales advantage, they will setup the thermal switch to turn the blower on as soon as they feel the stove is able to put out useable heat.

Therefore I would consider the "time to significant heat" to be the time it takes to go from initially lighting the fire in a cold, dead stove, to the time when the blower first kicks in.

Now with my old smoke dragon, I can consistently do this in 7-10 minutes if I push it a bit. By my standards, I would consider any stove that could go from dead to blower on in under 20 minutes to be functionally equivalent, and a reasonably fast heating stove.

Just to compare notes, what sort of times do the rest of you get?

Gooserider

Using the quick heat theory, a small box cast iron heater would seem the best. You would not get overnight heat from one fueling, but you would max the quick heat impact.

 

[Gooserider]

Yes, a small box probably would warm up faster than a big one, but it wouldn't put out as much heat once up to temp, and as you say wouldn't have the burn time.

The OP (in another thread) said he wants the long burn, plus needs more heat than you can get from a small box, so I believe that most of us were talking in the large ~3CF box range. We need to stay in size class, so put the baby box back in the playpen until it grows up...

Gooserider

 

[restorer]

Goose:
Are we preaching to the choir? Seems our questioner is no where to be seen. Are we arguing to be arguing? I still go for the small and fast.

 

[Bill]

No, the choir is in, I read every post, every day, and I have read all the articles that pertain to wood stoves, took me 60 hours. I have been burning wood over 30 years. The opinions, and expertise in this forum is extremely helpful in my decision in my purchase next week. Actually the forum picked my woodburner I was leading another direction and was straightened out.

I found it easier to buy a new car than this new wood-burner.

Thanks again for every-ones help, and I will review my stove, good or bad points in a fair and objective manor to help others in my position.

I asked a lot of questions the last two weeks, I had been given urban legends from other acquaintance's and ran them past our members and found out they were just that bs.

 

[babalu87]

Thanks for your replys, but my cabin is below freezing all winter until I start a fire. We do not keep it heated while not there, and in theory it could get below zero, depending on the weather. Just a concern thinking about a stove replacement.

That explains my question.

I think you would have to try and get it hot enough to crack it and even with all ones efforts unless you exceeded the manufacturers operation guidelines it would be about impossible to crack a well built cast stove.

 

[TheFlame]

Contrary to what most posts in this thread indicate, you can crack a cast iron stove quite easily.

I know of one case personally, a friend who cracked the bottom pan of his Jotul F600 Firelight. If you search this site, you will find others as well.

 

[Corie]

The bottom pan?

That's not even an area of high heat? Was he firing with the ash pan door open all the time or something?

 

[begreen]

By bottom pan, do you mean the ash grate? That is almost a certain sign of an air leak or intentional opening of the ash pan door.

 

[babalu87]

Contrary to what most posts in this thread indicate, you can crack a cast iron stove quite easily.

I know of one case personally, a friend who cracked the bottom pan of his Jotul F600 Firelight. If you search this site, you will find others as well.

Peter Gabriel is in agreeance with you.