Randomly hot overnight fires

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Dec 13, 2019
South Carolina
I occasionally have fires overnight which get really hot.

This is a Suburban insert, secondary combustion tubes have been added to it. It has an 8" single wall liner running 13' straight up a masonry chimney. Occasionally I will get a hot overnight fire - this past Tuesday I loaded it and went to bed. Woke up two hours later and internal flue temps were at ~650f, the side of the firebox was measuring ~430f (measured with K-Type thermocouples). Outside temp was about 50f. My wood pile is mostly oak, bradford pear, and maybe some hickory and pecan mixed in.

Most nights it will burn with flue temps in the 425-500f, firebox side at 325-350f. I set my air controls to the same spot every night.

It did this a few times last winter so this year I dollar bill checked my door gasket and it seems ok. The ashpan gasket was loose so I replaced it and it is now tight.

I can close the secondary and primary air and the stove will cool.

Anyone else experience this? Suggestions on how to manage it?

-Or perhaps should I even be concerned with it? It will sure make a load of wood disappear quickly!

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We see those temps regularly with our stoves. Why it happened is hard to say. Looser packing of the firebox, drier wood, strong winds, or a bit later closing down of the primary air could all cause this. It doesn't sound like anything to get excited about.
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@begreen thanks for the reply. It is surprising to see the temps at 12am when the house is asleep. My mid day awake self knows that those temps are not dangerous for the steel. Glad to know I am not the only one who has random hot burns overnight.
I noticed that you’re in North Carolina. I’m not exactly sure if you’re in the cooler part of the state in the mountains, but I would imagine that you’re typically not burning 24 seven. I say that because I wonder if the last load of wood you put in before bed happens to have the most hot coals compared to your earlier fires which results in quicker ignition, and may be overall higher temps that may be a little bit harder to dial back.
That said, the temps that you’re talking about are not very high and don’t sound very concerning.
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That is a good point. In Dec to Feb I will load the fire at 5am before leaving for work, it gets a small load around 4-5pm, then a full load again around 9pm. That 9pm coal bed is different than what I have in the mornings and different from what I have when I get home from work.
I’m in NC as well. I have some hickory that I burn. It seems to burn hotter in my stove that the Oak, Bradford, Pine or Ash. See if there is a correlation between a predominantly hickory heavy load vs one with less hickory if you are just randomly grabbing what’s on top of the pile.
What you described sounds perfectly normal. When burning in batches I would expect the stove temperature to gradually rise for several hours, then start to decrease once the fire reaches the coaling stage. 650F is perfect for an internal flue temperature.
How warm was the room? If it was cranking out too much heat, then just don't load quite so much wood next time.