Stove top temp is not always the best start up guide

[tfdchief]

And just for the record BG. I find what happened to you in your first post, is the norm for me. I pay very little attention to stove top temp. I look at it when the stove is settled and cruising, but I have to gauge my shut down on the looks of the fire and the flue temp. If I waited until my stove top temp was where I wanted it, the flue would have melted in a big heap.

 

[topoftheriver]

I think we are all on the same page. BG's first post illustrated the point. Just because the stove is barely warm doesn't mean you can keep firing it hard. The pipe smells hot at 1000, whether you have a thermometer to tell you it is hot or not. Use technology, but trust your instincts as well. That is all I am saying. Unfortunately, I have burned some stoves that had no pipe thermometer, or glass. My senses were the only thing to guide me.

Once again, plain and simple common sence. Just be carefull.

 

[Jon1270]

I wonder how many insert owners go through this ritualistically and have no clue otherwise

That would be me, sort of -- not that I operate my stove ritualistically, but I'm surely clueless about some of what is going on in my stove. This is my first year, and I have a non-cat insert. I check the stovetop with an IR thermometer, but there is no flue thermometer. My insert's manual doesn't say anything about flue temperatures (or stovetop temps, for that matter). In this forum it's easy to get the impression that flue thermometers are primarily of interest to those with cat stoves; with the discussions about cat and non-cat stoves mixed together, it's sometimes hard to tell whether a given piece of advice is relevant.

 

[begreen]

I think we are all on the same page. BG's first post illustrated the point. Just because the stove is barely warm doesn't mean you can keep firing it hard. The pipe smells hot at 1000, whether you have a thermometer to tell you it is hot or not. Use technology, but trust your instincts as well. That is all I am saying. Unfortunately, I have burned some stoves that had no pipe thermometer, or glass. My senses were the only thing to guide me.

Exactly right chief. I took a look at the fire and the flue temp and closed down the air significantly. I ignored the stove top temp, but recorded it to share here. Doug fir can take off quickly. You need to pay attention to the fire first and foremost when burning a resinous species of wood.

 

[begreen]

That would be me, sort of -- not that I operate my stove ritualistically, but I'm surely clueless about some of what is going on in my stove. This is my first year, and I have a non-cat insert. I check the stovetop with an IR thermometer, but there is no flue thermometer. My insert's manual doesn't say anything about flue temperatures (or stovetop temps, for that matter). In this forum it's easy to get the impression that flue thermometers are primarily of interest to those with cat stoves; with the discussions about cat and non-cat stoves mixed together, it's sometimes hard to tell whether a given piece of advice is relevant.

Insert owners have a real challenge because it's not easy to instrument the insert. They need to rely on visual observation first.

 

[Augie]

I picked up some 650 degree rtv.used it to seal the singlewall It is up the flue 4ft. If the flue gets over 650 it off gasses a bit and my smoke alarm goes off. Not intended but it is nice as a backup. I have used it twice.

 

[pen]

I picked up some 650 degree rtv.used it to seal the singlewall It is up the flue 4ft. If the flue gets over 650 it off gasses a bit and my smoke alarm goes off. Not intended but it is nice as a backup. I have used it twice.

Using RTV there is not suggested. Furnace cement is the way to go.

pen

 

[Jon1270]

They need to rely on visual observation first.

So what's the best written description you've seen of what one should visually observe? I've read several articles here and at woodheat.org, and spent a lot of time staring at fire in the last few months, and while I'm getting better at recognizing when it's too soon to turn the air down, I'm uncertain what 'you should've turned it down already' looks like.

Elements of what I see and try to interpret, not necessarily in order of appearance:

• Flame colors, which are sometimes partly blue but are usually / mostly along a spectrum from bright yellow through a dark, reddish orange. From what I've read, blue indicates a thoroughly oxygenated flame, with clean, complete combustion, whereas yellow/orange flames indicate incomplete combustion. Yellow flame is hotter, reddish flames are cooler. Too much dark / reddish flame suggests that some smoke is escaping unburnt.
• Overall volume and location of flames -- there might be only a small amount, coming from specific pieces of kindling or fuel, or the firebox could appear completely full of flame, or anywhere in-between. So long as the fire is not especially cool and smoky, this is probably a good indicator of how much the fuel is currently offgassing.
• Movement of flames - can be slow and lazy, dancing around energetically, or being beaten around like a flag on the prow of a fast boat. I take this to be air turbulence made visible, and a good indicator of how much air is being sucked through the stove and sent up the chimney.
• Presence and amount of secondary flames, i.e. flames that get bigger when they arrive at the secondary air tubes and spread out under the baffle. Indicates the baffle and air tubes have reached some threshold temperature.
• Movement of secondary flames around air inlet holes - again, could be lazy or vigorous. Sometimes air is coming through the inlets so fast that it blasts a neat row of small, round holes through the secondary flames. I haven't yet grokked what this might mean.
• Flame may or may not be licking around the front of the baffle and continuing up towards the chimney. I assume it's best that there's not too much of this, as heat from combustion that happens too close to the chimney outlet is probably wasted.
• Fuel surfaces might look like unscathed wood, or be blackend, fractured like parched earth, glowing and/or covered in ash.

Which of these (or what else) do you look for as indicators of likely stack temperature, or of what you should do with the air adjustments?

 

[tfdchief]

Which of these (or what else) do you look for as indicators of likely stack temperature, or of what you should do with the air adjustments?

Looks to me like you have covered it quite well. I really don't think there is much to add to your list. You are very observant and therefore seem to have a pretty good grip on things. The only thing I would add to the list is the amount of radiant and convection heat (if you have a blower) that is coming from the stove. I think our human senses work better than we give them credit for sometimes. You know the difference between cool, warm, hot, and super hot. If you are sitting in front of your insert working on getting the fire settled in and cruising, and you are starting to sweat, it IS probably time to dial it down another notch

 

[tfdchief]

Exactly right chief. I took a look at the fire and the flue temp and closed down the air significantly. I ignored the stove top temp, but recorded it to share here. Doug fir can take off quickly. You need to pay attention to the fire first and foremost when burning a resinous species of wood.

I have even found that it happens and I can't explain it. A couple of mornings ago, I was starting up and had the same species, number of splits, coals, etc. that I always do in the stove in the morning, and I could not hardly keep flame (pouring the air to it) and the stack temp just kept going up. When it got to 1000 and still not enough fire or heat in the fire box to crank everything down, I opened the door. That of course, finnally, got the fire going and the stack temp down. But none of it made any sense. Next morning......back to normal

Edit: And no, there was no fire in the stack. It is clean.

 

[Huntindog1]

Some other things to take note:

How big a coal bed did you load on.
How hot was that coal bed, I usually can tell by how much it fries my face trying to get the coals raked and stove load. Sometimes the heat is intense coming off those coals.
What kind of wood , Size of wood splits, dryness of wood did you load. You can tell dryness by the approx weight and feel of the wood and knocking two pieces together for a sound check.
How tightly is the wood packed in the stove, is there much air space between pieces.
How fast did the wood fire up.
How much head space did you leave as the smaller spaces up around he burn tubes in top will heat up much quicker and easier once secondary flames start. If the stove is half loaded and lots of head space it will heat up slower. Plus stacking wood high in the front of the stove partially blocks exit path for the heat going up the flue which will cause the stove to heat up faster and can cause it to get too hot sometimes.
Did you load North South or East West or load cabin style criss cross pattern.

 

[Jon1270]

I just found a very interesting document from the US Forest Products Labbroken link removed)

If there is no pilot flame or its equivalent to ignite the gases, there may be
no flaming until pyrolysis in zone C is nearly complete and the emission of
gases slows sufficiently to let air make contact with the charcoal layer. Since
charcoal does not melt below 3480° C. or boil below 4200° C. (6 7), it cannot
go forth to meet the air for its combustion, but must burn in place as air
reaches it. Nevertheless, charcoal is an excellent absorber of radiant heat
and has a lower temperature of spontaneous ignition than any of the other major
products of pyrolysis. Thus temperatures of spontaneous ignition for mixtures
with air between the limits of flammability are reported as 644° to 658° C. for
carbon monoxide, 580° to 590° C. for hydrogen, 566° C. for acetic acid, 539°
to 750° C. for methane, and 430° C. for formaldehyde (6 7). Pine tar is said
to ignite spontaneously at 355° C. But for charcoal spontaneous ignition is reported
at temperatures as low as 150° to 250° C...

So it seems that resins, particularly pine tar, ignite at much lower temperatures than other gasses given off by burning wood. Maybe the bottom of the stove pipe / liner, being lighter gauge steel, can reach that resin ignition temperature sooner than the more massive, lower parts of the stove around the firebox, encouraging a zone of early combustion there?

 

[dentman4411]

Thanks for posting BG.... as a new burner with no previous exp. with stoves and no neighbors to speak of Ive learned the ropes in a "trial by fire" no pun intended.

While the damper is open I look to the single wall pipe (magnetic thermo and IR temp meter) as my primary indicator of ALL things regarding the stove. On a cold start, I let it run up to and maintain about 400-500 degrees until my stove top hits 500. If single wall goes past 500 I cut air back. I dont like the idea of that kind of hot air passing through my ceiling joists.... even though the duravent is rated for 1000 degrees continuous. I use and keep in the hand a cheap egg timer until I close the damper. This is a hard and fast rule for me as Im easily distracted by TV, internet, nature, photography... you name it. Timer stays with me on 4 minute intervals until i close the bypass. once damper closed I have found the stove really likes 650-700 degrees and even then the single wall is barely 250. It may seem like alot but really it isnt, on a cold start i have the damper closed insidde of 20 minutes. I think thats a reasonable amount of time to avoid a runaway stove.

 

[Jon1270]

How far up the flue is it necessary to mount a flue thermometer or sensor?

 

[Seasoned Oak]

I wonder if there is any chance of "welds cracking" when warming up a cold stove too fast?

 

[dentman4411]

How far up the flue is it necessary to mount a flue thermometer or sensor?

ive found the general consensus is 18" above the stove top for magnetic thermometers. Regarding the probe, i would guess its manufacture specific.

 

[Jon1270]

ive found the general consensus is 18" above the stove top for magnetic thermometers.

For an insert, that would be well above the block-off plate. I suppose you could surface-mount a thermocouple up there, with the wires finding their way to a digital display somewhere. I imagine a probe protruding into the flue would be completely out since it would be impractical to remove it for chimney cleaning.

 

[begreen]

For an insert, that would be well above the block-off plate. I suppose you could surface-mount a thermocouple up there, with the wires finding their way to a digital display somewhere. I imagine a probe protruding into the flue would be completely out since it would be impractical to remove it for chimney cleaning.

If I was using electronics I would definitely do a probe in the flue pipe. We have double-wall so surface mount is not going to cut it. You simply remove the probe temporarily when cleaning the pipe.

 

[Jon1270]

You simply remove the probe temporarily when cleaning the pipe.

But not so simple if it's above a block-off plate, which itself can't be accessed without pulling the insert.

 

[begreen]

I just found a very interesting document from the US Forest Products Labbroken link removed)

So it seems that resins, particularly pine tar, ignite at much lower temperatures than other gasses given off by burning wood. Maybe the bottom of the stove pipe / liner, being lighter gauge steel, can reach that resin ignition temperature sooner than the more massive, lower parts of the stove around the firebox, encouraging a zone of early combustion there?

There was no coal bed when I started the fire yesterday. It was a cold start. If it was on a warm cold bed (like today) the stove top would have already been at least 200F. What happened yesterday was just the right amount of air space between some very dry and resiny wood loaded N/S that ignited quicker than normal. The fuel was fir and the resins had fully ignited, in the firebox. It was only about 42F yesterday morning so draft was normal, though the chimney had been cleaned the week before.

This morning, the same wood was loaded on a decent sized coal bed, loaded E/W. Stove top at 225F. It has been a total feline-cat normal startup with the air being closed down in about 10 minute intervals. The stove pipe never saw over 500F.