How Hot Is Too Hot???

Jash Here,

After allot of reading of different post on this site(a huge help and learning tool) one phrase keeps cropping up over and over,

Over Firing

I'm posting a question to "clear it up" :
What's to cold,,,,warm,,,,,just right,,,,,HOT,,,,,over fire (TOO HOT),,,, and the "HONEY CALL THE FIRE DEPARTMENT I JUST SET THE STOVE ON FIRE
nfire: Melt Down nfire: temperatures?

For how long do those temps have to be "at" for the effects to become apparent?

1.) for hand fired stoves (mine is a Russo C35...it will hold 35lbs of coal)

2.) for stoker stove's (semi-automatic)

steel vs. cast iron stoves

With some good data it would make it a whole lot easier in knowing when the Stove heat is pushing the ragged edge of safe.

Thanks
Joel

Hey jash
Good question.

We have run our keystoker 90K (Steel construction) at around 500-550 Deg. F on the sides with a magnetic type thermostat. The exhaust was 250-270 (internal pipe temp) without a baro damper. It was quite hot and burning pretty good when it got really cold outside (-10 to +10 deg. F).

There is an internal Hi Limit Switch on the convection fan set at 200 to stop the stoker, ie) too hot or if the fan fails to pull the heat off the stove.

As for meltdown temps? I hope I don't have to find out.

I'm using a Harman SF 250 hand fired burning nut.

I find most efficient use of the stove when it is at a simmer.
Warm air from fan will be 175F -180F. Stack will be 175F -200F. Damper is usually at 3/4 to one full turn open.

For cold days and nights I open the throttle 1.5 to 2 turns.
Air temps 200-230F. Stack temps 250F-290F.

I've opened the damper over two turns for extended periods of time
Air temps 300F from fan. Stack temps 400F.

I can probably push 350F for extended periods from the air vents BUT I would consider this to be TOO hot for the stove & my comfort ( mentally speaking ) level as you can smell the stove cooking. I do not know what the sidewall surface temps are as I have no way of testing, but easily over 500F.

My stove differs from a stoker in such as the air vent temps creep up as the coal fire ages 4 or 5 hrs. Once the entire bed is glowing, temps climb 30F-50F.

Steel and cast iron need to get to red hot temperatures to soften enough to be deformed.

I don't know what temperature will turn mild steel or cast iron red hot or if the temperature is the same for the two metals.

I'm sure that a stoker stove would be near impossible to get too hot. The stove flue pipe may get hot enough to burn off galvanizing with a hand load or wood fire, but a stoker fire can only be so big, and has it's limited air supply, so the amount of heat is limited by it's design.

A hand load stove if given a good load of coal and unlimited air can definitely get hot enough to turn steel to red heat.

From personal experience, a wood fire can turn a stove to cherry red, and permenantly warp panels of 1/4" steel. This was with a door left open for too long.

So near-to red hot is the danger point, maybe one of the forum members knows at what temperature steel and cast iron turn red.

Greg L

.

I did a google search for steel and found out that red heat starts at around 1290* F or about 700* C.

What is the highest temp on the magnetic stove thermometers?? I don't own one. Just use a laser thermometer.

I used a probe thermometer, and found the hand load coal fire in my boiler to be above 1600* F.

I'm going to go out and see what the fire in the stoker is producing.

Greg L

.

I would think as long as the fire is contained in the firebrick, that the most you could do is warp the unit, and/or crack it in the case of cast iron. The risk of actually melting anything outside the firebox is pretty miniscule.
That said, it is easy to melt steel in a coal fire, I do it all the time. I believe that somewhere I read that a coal fire will run up to 2200-2400F. Temperatures like that will make glass woozy.

I have had my firebox probe reading 1000F like it was a few minutes ago, as the probe sits 2" above the fire brick line. ( 10 hrs since last load ) After I shovel in a fresh load, the fire box temps will drop dramatically to 400F. This thermometer reads to 1200F and I have had it pegged when the coal level drops and it is completely burning.

I do not think it's the temperature of the fire but the volume of coal and to what percentage it is burning combined. If my box is at 30% capacity and blazing away everything is fine. But if I fill her up and leave the ash pan door open for 15 mins, you'd better stand back. It's can get scary hot

I had an instance last week where I left the ash door open,
and shook and filled the stove, and left the room, and
forgot about it until the smoke detector went off. I thought
something caught fire!
anyway, when I got downstairs where the stove was,
the stack temp was in the red on the gage, probably
well over 500, and I have no idea what the stove temp was,
but she was goin good to say the least. closed the door,
and the temps backed off almost immediately, and the
smoke detector went off when I walked by it.. so I think
it was mostly from some dust geting cooked on the pipe or
stove. I didn't see any evidence of red metal, or
smoke anyplace though.
but still scary just the same

Scary is when your stovepipe is yellow and glowing, that's about 1100-1200F so I'm sure the firepot was close to twice that.

Coaledsweat: you too?? This happened about 25 years ago:

I came home from work, tossed a few small splits of oak on the bed of coals in the big wood stove, left the door open to get it burning well. Then..
I got a phone call, back in the days that phones had cords, so I was tethered in the kitchen. About twenty minutes [call from girlfriend] later I noticed a 'hot metal' smell. Set the phone down looked around the corner to see the yellow flue pipe, the top of the stove warped like a 33rpm LP record left in the sun, and a 1" gap between the warped down side of the flue collar and the end of the flue pipe: unlimited oxygen to the fire in the chimney.

I slammed the loading door shut, but the fire in the pipe was going strong, I saw an orange glow on the snow on the back deck, slid the door open and looked at the top of the chimney, it was an 8' diameter ball of flame, looked like the 'onion top' on a Russian Mosque. And the fire was roaring like a wild animal.

I had a big CO2 fire extinguisher that I discharged into the gap at the base of the flue pipe and the warped flange on the stove top. This put out the chimney creosote fire.

My neighbor came busting through the front door seconds later with a huge fire extinguisher, yelling at me that my %%$%&&^ phone was off the hook!!

My girlfriend was a bit confused when I finally got back on the phone.

I never did get the warp completely out of the stove top, even using a hydralic 'porta-power' to jack up the low side and beating on the high side with a 16# sledge. Even with heat applied from a huge rosebud tip on my oxyacetylene torch.

A good learning experience that could have been a disaster!

Never, ever walk away from an open ashpan or loading door!!

Greg L

.

Here is a chart with the color of steel at various temperatures so you

can judge how hot it is. Others have said they observed temps of

1000 on their stacks then you should see a faint glow on the pipe.

Could anyone see the faint glow @ 1000 ? Could be the fly ash or carbon

actually insulates the pipe from the extreme temperature so a pipe

temp guage may not read accurately,probably several hundred degrees

too low.Also the laminer flow is slow on the inside wall of the pipe and

the true temperature is in the center of the pipe,where the true temp

should be read.

http://www.marshallarts.co.za/temptable.htm

Ted BigBarney

Wow, that thing was a lot hotter than I thought!

Scary stuff.

1300 is a good number to watch out for, I had no idea how hot was too hot. My stack thermometer says over 600 is “over burn”. I turn to keep my stack temp 650-700 when I’m burning my hardest (about 160 lb / day).

In my accidental over burning I have had my magnetic thermometer on my stove’s cast go between 800-900 degrees (that is with firebrick) and with the stack mag thermometer (I have two) about 750-800. My galvanized isn’t shiny anymore. I never noticed glowing red on the stack or cast. I could see 1300 can be attainable with my stove if I left it go with a full load wide open for too long.

A friend of mine has a Harman Mark III. Well......... he always burned wood in it until I convinced him to start burning coal. He told me the steel baffle in the top of his stove was bent like a banana and it was laying in the ashes (it fell out of the top of the stove). I told him he must of overfired the stove. (Just a guess, I have a stoker not a hand fired) Does this sound correct. A guy from the place he bought it replaced the baffle and said he didn't know why this happened. What do you guys think?

Ed--Are you telling us, your buddy's Mark III was almost new? Was in under warranty?

The baffle on my old Mark III were slightly warped but never appeared as if they could fall out. I never heard of a Harman coming apart. Somebody missed a mig weld?