Burning in a Jotul Castine F400

[pdxwoodlover]

Moderator: Posts moved to a Castine operation thread.

The Castine starts secondary combustion pretty quickly. I started out going by stovetop temp for closing the air down but found that it took a long time for the thick stovetop to warm up. Meanwhile, the fire was showing me that it was time to start closing down the air. This could be with a 250º stovetop on a cold start.

Thanks, begreen, that’s a good point. Would you say it’s okay to start closing the air down once the secondaries have started? Up to now I have been waiting until stovetop temperatures reach ~400 degs on my Castine before closing the air down gradually, but by that time the fire is usually pretty much roaring and I would imagine that flue temperatures might already be pretty high. I don’t have a flue thermometer to check, as my stove sits right outside an old masonry fireplace opening and the pipe exiting the stove almost immediately disappears behind the block off plate and up the masonry chimney:

So I don’t know where a flue thermometer could even go and also be readable? (I realize that this question is a bit off-topic.)

bigealta, thank you for the nice video. I saw that you stack your splits almost all the way to the tubes. Just the other day I realized that those two protruding pieces on the back wall of the Castine are actually markers indicating the maximum load height (the words “maks vedinlegg” written on the wall mean “max wood insert” in Norwegian, according to Google Translate). Do any of you Castine owners actually heed that guidance? Seems like it would not allow for a very full firebox.

Thanks everyone, this is such a great forum.

 

[bigealta]

Never noticed that or knew about the stacking height mark. I have been concerned about the wood being so close to the baffle, but the kindling does not get as hot as the splits when they coal, and it burns down and away from the baffle pretty quickly. The high heat is with the coals. So my thought is if the large coals stay far enough away from the baffle it should be ok. As a blacksmith you can only heat metal in the coals (coal forge), to get it hot enough to work. Metal kept out of the coals and just in the flames would never heat up hot enough. But then again, a Gas forge flame will easily heat the metal red, orange, yellow and white hot. Would love to hear other's thoughts.

 

[bigealta]

Never noticed that or knew about the stacking height mark. I have been concerned about the wood being so close to the baffle, but the kindling does not get as hot as the splits when they coal, and it burns down and away from the baffle pretty quickly. The high heat is with the coals. So my thought is if the large coals stay far enough away from the baffle it should be ok. As a blacksmith you can only heat metal in the coals (coal forge), to get it hot enough to work. Metal kept out of the coals and just in the flames would never heat up hot enough. But then again, a Gas forge flame will easily heat the metal red, orange, yellow and white hot. Would love to hear other's thoughts.

Ok here are the Height Markers. I’m definitely loading above those.

 

[pdxwoodlover]

Ok here are the Height Markers. I’m definitely loading above those.

I know, these markers seem awfully low. I’m not sure what to make of them. Even the official Jotul YouTube channel has a video for loading the stove (it’s actually the Oslo in that case, but I suppose the concept should be similar) that shows a pretty tall stack of splits, surely above where I’d imagine the marker to be. Also, I don’t recall any mention of the markers in the manual. So it’s probably safe to ignore them.

 

[bigealta]

Just had and “almost” over fire situation. I was so busy taking the video of the 1st time I had strong secondaries with the draft Fully closed, that I completely missed the obvious.

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[pdxwoodlover]

Note the stove top temp. This is why it is not helpful in a cold start. It takes time to heat up the mass of the stove, while the flue temp is already very high.

I'm a little confused here. The manual for my Jotul F400 states that the top surface (measured in an off-center location) should reach 400 degrees before turning the air down. I think the rationale is that one wants robust secondaries before reducing air flow. But from begreen's analysis it sounds as though one would want to start turning the air down quite a bit sooner to avoid excessive flue temperatures and a potential overfire situation down the line.

I don't have a flue thermometer, just a magnetic surface one, so I can't monitor flue temperature. But I've observed secondaries starting before the top has reached 400, so I suppose that means it's OK to turn the air down earlier. Any insights on this?

And this might be a naive question, but is it harmful for flue temperatures to get quite high on a cold start? I can understand that one doesn't want to overfire a cast iron stove (risk of cracking and such), but what would be the issue with high flue temperatures?

Thank you for any advice.

 

[begreen]

I don't have a flue thermometer, just a magnetic surface one, so I can't monitor flue temperature. But I've observed secondaries starting before the top has reached 400, so I suppose that means it's OK to turn the air down earlier. Any insights on this?

Yes, particularly on a cold startup. The mass of the stove can take much longer to warm up than the firebox. There were many times when I started turning down the air on the Castine well before the stovetop reached 400º.

And this might be a naive question, but is it harmful for flue temperatures to get quite high on a cold start? I can understand that one doesn't want to overfire a cast iron stove (risk of cracking and such), but what would be the issue with high flue temperatures?

That's a good question. The harm would be if the flue system experienced high temperatures above its rating for an extended period of time.

 

[bigealta]

The F400 is pretty temper mental for me. Sometimes secondaries work great for quite a while, other times i'm fighting to get them. All from Same stack of oak. But a good hot stove and good airflow between the splits seems to greatly increase the success rate. i use the fire to guide the air control setting, with the flue temp gauge as a helper, especially for overfire protection. A nicely burning fire can look the same at both hot and crazy hot.

 

[pdxwoodlover]

The F400 is pretty temper mental for me. Sometimes secondaries work great for quite a while, other times i'm fighting to get them. All from Same stack of oak. But a good hot stove and good airflow between the splits seems to greatly increase the success rate. i use the fire to guide the air control setting, with the flue temp gauge as a helper, especially for overfire protection. A nicely burning fire can look the same at both hot and crazy hot.

I agree that air flow between the splits really helps. I usually try not to stuff the firebox too densely with large splits, or else some of the splits don't even really properly catch flame, they just kind of slowly break down into embers as the burn progresses.

My secondaries are typically pretty robust. But I find myself having to watch the stove a lot to make sure it doesn't get too hot. Fairly often it is cruising in the 625-650 degrees territory. Which, I suppose, might actually be a normal operating temperature for this stove, despite the 400-600 degree range that is typically quoted as ideal.

 

[EbS-P]

Glad to know what the tabs are for. I will continue to load as much as I can. Touching the baffle really disrupts a good burn. So I don’t do that (very often). I think it’s my wood has more effects on the burn than anything else. Size, species, moisture....
On a load of tulip poplar I can cruise at air full closed at 450 stove top. Other night an a load of really sappy really dry Long leaf pine the front deflector was glowing. 900 degrees on the top in the center 650 on the corners. Don’t want to do that again. Wettish wood equals crap shoot burn. Nothing is predictable.

 

[begreen]

My secondaries are typically pretty robust. But I find myself having to watch the stove a lot to make sure it doesn't get too hot. Fairly often it is cruising in the 625-650 degrees territory. Which, I suppose, might actually be a normal operating temperature for this stove, despite the 400-600 degree range that is typically quoted as ideal.

It's a very willing stove. We had one before the T6. You will get better at controlling the fire in part by the load size, wood thickness and closing down the air sooner. Our stove typically cruised in the 550-700º range with a full load.