Secondaries???

[Trooper]

If stove temps need to be at about 1000F for secondaries to occur, why does the thermometer stop at 700?

At 700F and above it says "Too Hot". Last night I had my insert up to 700 but didn't want to push it just to see if I could get secondaries.

 

[BrotherBart]

Moved this to a new thread. Good subject.

Surface temp is usually around half of the temp in the firebox. Secondary combustion with dry wood occurs around 1,100 degrees inside the firebox. The dryness of the wood, under 25% or so moisture content, affects or prevents it. If the wood is not dry enough the evaporating moisture will prevent secondary combustion at pretty much any temp in the firebox until the wood drys out.

 

[n3pro]

IF i'm reading the question right, because stove temps should be between 500 - 700, 1000 + is glowing and if too high too long will cause damage. The highest I ever seen was slightly over 800 and I was in panic mode. Firebox temperature however does need to be over 1,000 which is what the baffle and firebrick help to achieve. I never seen a thermometer that read firebox temperature. From a hot start I have gotten secondary action under 500.

 

[Sprinter]

My thermometer (Condor) stops at 900. But still, if your stove top gets to 700, you better do something about it. Now. The temp of the outside surface of the top is way cooler than the the internal firebox temp where the secondaries are.

Also, where do you have your thermometer? Sometimes proper placement can be a problem on inserts.

 

[Trooper]

From a hot start I have gotten secondary action under 500.

n3pro - are you saying that you have achieved secondaries under 500F as measured inside the firebox, or stove top?

But still, if your stove top gets to 700, you better do something about it. Now. Also, where do you have your thermometer?

Sprinter - my thermometer on a 'ledge' just above the firebox door. I agree that with inserts placement can be tricky. What should I be doing differently in the future? Damping the air down sooner?

 

[akbear]

There really ought to be a better standard (and easily affixed and maintained) way of indicating a fire that's getting too hot from one that's beneficial to the system (or not in danger of creating buildup). Not even thinking about inserts, stoves these days have such a range of differences, from those that have insulated or baffled tops all the way to something like mine where it's a sheet of glass ceramic cooktop. It's one of those things where the old rule of thumb just plain may or may not apply.

Perhaps they could come up with something like the turkey pop-up indicator, only maybe something resettable since I imagine a lot of us shy away from disposable things that must be replaced everytime (no matter if it's good for me or not, I was certainly peeved when my combination smoke/CO detector would not stop beeping and found out they have a timer on it to make people replace them after so many years)

 

[oldspark]

"If stove temps need to be at about 1000F for secondaries to occur, why does the thermometer stop at 700?"
Wow, not sure how you got the wrong idea about secondaries, takes a reasonable skill set to run a woodburner safey so education is first on the list of things to do before installing a stove, cutting wood and building a fire for the first time.

 

[begreen]

The confusion may be because it is not entirely clear where the measurement is taken. My guess is that 1000 is a firebox temp in this case. The problem is that most folks have no way to measure the firebox temps, so for discussion sake maybe it's better to speak in terms of stove top temperature only.

 

[oldspark]

That exactly what I ment BG, most articles I have read abut the temps needed to produce secondaries stated it was in the fire box not the outside temp, confusion is good as long as people learn from it.

 

[My Oslo heats my home]

I was gonna say the same thing, if someone is getting 1,000 deg on a surface temp, that stove would have to be cherry red and ready for bad things about to happen.
I have had the top plate on mine get a slight glow, but only a few times since owning it.

 

[begreen]

The Castine would sometimes fire off secondaries on a start up at around 250F stovetop temp. I never took that stovetop over 800F. That was plenty hot enough!

 

[oldspark]

With certain woods I can get secondaries around 300 degrees or so stove top but takes a while for the stove to heat up so the internal temps may be higher in relation to stove top temps at that point in time (start up).
Less dense woods seem to give up their gases quicker then the more dense woods.

 

[BrotherBart]

A lot has to do with firebox size. A smaller firebox gets hotter faster inside than a large one. While the stove body heats at around the same rate on either one. I have seen it over and over. The little F100 almost starts secondary burn by the time the fire starter burns out. The F3 takes a while longer. The 30-NC takes longer still. But all three take around 30 minutes from a cold start to get to 500 stove top temp.

 

[begreen]

Good point. The T6 takes about 5-10 minutes longer to start firing off the secondaries than the F400 or F3CB did. I also start the fire with larger splits in the T6.

 

[Trooper]

Thanks for the responses everyone. I should have realized that temps inside the firebox were different (higher) than those read by the thermometer on the insert's ledge. Also I was burning 3-4 medium splits of oak, measured at 10% MC, so wet wood was not the cause of the lack of secondaries.

Clearly there are a lot of variables from stove to stove, and clearly I am new to burning . Should I just stick to learning my stove for now, and not worry too much about the secondaries? What is the benefit of having secondaries...is it proof of a hot, efficient fire?

 

[Sprinter]

Also I was burning 3-4 medium splits of oak, measured at 10% MC, so wet wood was not the cause of the lack of secondaries.

10%? That's got to be pretty close to equilibrium, but having spent a year in Arizona, I believe it

 

[Sprinter]

Thanks for the responses everyone. I should have realized that temps inside the firebox were different (higher) than those read by the thermometer on the insert's ledge. Also I was burning 3-4 medium splits of oak, measured at 10% MC, so wet wood was not the cause of the lack of secondaries.

Clearly there are a lot of variables from stove to stove, and clearly I am new to burning . Should I just stick to learning my stove for now, and not worry too much about the secondaries? What is the benefit of having secondaries...is it proof of a hot, efficient fire?

Secondary burning is the burning of the incomplete combustion products like smoke and gasses, that otherwise would go up the chimney, but still have a lot of heat potential. That's what makes modern stoves so much more efficient. You'll see the effect of secondary burning by pretty colored flames around the secondary tubes. You can find a lot of pictures posted on the forum (and on youtube) of secondary burning.

It does take about 1100F temperatures to affect the burning of those products.

You have good questions. The more you learn about this stuff, the more successful you'll be, and the more fun it will be as well.

 

[begreen]

Thanks for the responses everyone. I should have realized that temps inside the firebox were different (higher) than those read by the thermometer on the insert's ledge. Also I was burning 3-4 medium splits of oak, measured at 10% MC, so wet wood was not the cause of the lack of secondaries.

Clearly there are a lot of variables from stove to stove, and clearly I am new to burning . Should I just stick to learning my stove for now, and not worry too much about the secondaries? What is the benefit of having secondaries...is it proof of a hot, efficient fire?

It's not the wood if that is measured on the freshly split face of the wood and not the end grain. Could be weak draft. How tall is the flue on the stove? What were the outdoor temps when you were burning?

 

[Ashful]

There really ought to be a better standard (and easily affixed and maintained) way of indicating a fire that's getting too hot from one that's beneficial to the system (or not in danger of creating buildup).

There is, and it's called, "RTFM." Stove designs and manufacturers vary in this regard, but most have an entire section of the manual dedicated to this subject.

 

[Sprinter]

There is, and it's called, "RTFM." Stove designs and manufacturers vary in this regard, but most have an entire section of the manual dedicated to this subject.

Well, the manual is a good starting point, but there's no way a manual is going to cover all the bases and answer all the questions. That's why forums like this are so helpful. Most, maybe all, manufacturers shy away from even giving you a specific temperature that qualifies as "overfiring". To me, there's no reason to allow a stove top to get above about 650F, and that should keep most of us out of trouble and efficient.

 

[begreen]

Unfortunately stove manual's quality of info on burning varies from boiler plate techniques to good details on the fire, wood, temps etc.. Sadly, most manuals do not mention specific stove top temps or show where the thermometer should be located. And very few discuss the different burn stages.

That said, at least Napoleon took the time to describe the combustion process, a detail often omitted in manuals.

 

[Sprinter]

The Castine would sometimes fire off secondaries on a start up at around 250F stovetop temp. I never took that stovetop over 800F. That was plenty hot enough!

FWIW, that has been my experience with the Super27 as well. My secondaries usually start by the time the top gets to 250 or so.

 

[Sprinter]

Although 10% MC is possible, especially in your climate, it's pretty uncommon, so it may be worth asking how you are measuring it. You need to make a fresh split and measure in the middle of the open face. And what does the meter show when you lay the pins on the palm of your hand? It should be in the mid 30's.

 

[oldspark]

Monitoring flue temps go a long way with efficent wood burning.

 

[Trooper]

Although 10% MC is possible, especially in your climate, it's pretty uncommon, so it may be worth asking how you are measuring it. You need to make a fresh split and measure in the middle of the open face. And what does the meter show when you lay the pins on the palm of your hand? It should be in the mid 30's.

Hi Sprinter,

Just measured the palm of hand: 30.8%
Just made a fresh split from same 'batch' as last night, and measured in the middle of the open face: 9.4%
I know it seems low, but keep in mind:

• Low equilibrium MC here to begin with, but not sure of the exact number
• I am only allowed by the USFS to take dead and downed wood
• This batch was c/s/s 2-3 years ago

My chimney is 16 feet high. Outdoor temps at the time of the fire were 55-58; not that cold but I wanted to finish my burn-in fires while I could still keep the doors/windows open, and before it got really cold.

I may have had secondaries last night and not seen them, but I have seen enough video to know what they look like. Perhaps draft wasn't what it should have been but then why did I not have smoke, and why did the fire crank up so hot?

Great comments from everyone...thanks again.