Starting a fire

St. Coemgen

Feeling the Heat
Feb 4, 2016
323
Hungary
www.stcoemgen.com
There are 3 instruments shown.
  1. A Condar probe thermometer on the double-wall stove pipe.
  2. The stovetop temperature on a Sandhill thermometer
  3. A digital probe readout for the flue using an Auber AT100
IMHO - the only one that matters is the stove top (2). Because that is what is mostly heating your space.

The others simply show temps of flue gas, which can be quite high even at startup (and especially at startup since then the most air is added). But that really mean little. As startup flue gas temps do next to nothing to heating your space with a double walled stove pipe which you seem to have.

So exactly... what was the point of this post?
 
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ABMax24

Minister of Fire
IMHO - the only one that matters is the stove top (2). Because that is what is mostly heating your space.

The others simply show temps of flue gas, which can be quite high even at startup (and especially at startup since then the most air is added). But that really mean little. As startup flue gas temps do next to nothing to heating your space with a double walled stove pipe which you seem to have.

So exactly... what was the point of this post?
Flue temp is extremely important in the safe operation of the stove, mainly so the safe operating limits of the stove pipe are not exceeded.

It is also important in the efficient operation of the stove, spiking the flue at say 1200F while heating up the stove may warm it up faster, but also sends over 50% of the heat from the wood straight up the flue.

Flue temp also gives an indication (within reason) of what the stove top temp is, assuming it is understood that the stove top temp lags behind changes in flue temp. Which again goes back to safety, because its easy to have a spike of 1000+F in the flue, and never see that on the stove top.
 

St. Coemgen

Feeling the Heat
Feb 4, 2016
323
Hungary
www.stcoemgen.com
Flue temp is extremely important in the safe operation of the stove, mainly so the safe operating limits of the stove pipe are not exceeded.

It is also important in the efficient operation of the stove, spiking the flue at say 1200F while heating up the stove may warm it up faster, but also sends over 50% of the heat from the wood straight up the flue.

Flue temp also gives an indication (within reason) of what the stove top temp is, assuming it is understood that the stove top temp lags behind changes in flue temp. Which again goes back to safety, because its easy to have a spike of 1000+F in the flue, and never see that on the stove top.
First, modern stoves and flues are designed to deal with high temps. Extra high temps are mostly only found in a chimney fire, and any modern flue should also be coded to deal with a chimney fire.

Second, none of the temps reported get anywhere near the temps you report "of concern".

And clamming flue temps are a definiton of "efficiency" are dubious. Most efficiency in a modern stove happens in the stove, not in the flue. Catalytic stoves, as just one example. If you have a bot bellied stove from 1880, then you may be correct. But if not....

And even short term high temps are also suppose to be coded into the flue by code. So are also okay, and within safety margins (if the flue was installed to code). That is, flue temps are only needed for the neophyte (and as a backup if you never cleaned your flue and have a chimney fire). After a while, you should "get it", and learn how to deal with your stove properly.

So the flues, if modern, already are coded into spikes in temps, etc.. Even to the extremes you mentioned.

If one is running temps at such extremes constantly, then they are doing something wrong.

And again... These were start up temps. These always get the most blasts of air, and are often a lot hotter then "constant running" temps. So you need to put that into perspective.

Hope this helps.
 
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ABMax24

Minister of Fire
First, modern stoves and flues are designed to deal with high temps. Extra high temps are mostly only found in a chimney fire, and any modern flue should also be coded to deal with a chimney fire.

Second, none of the temps reported get anywhere near the temps you report "of concern".

And clamming flue temps are a definiton of "efficiency" are dubious. Most efficiency in a modern stove happens in the stove, not in the flue. Catalytic stoves, as just one example. If you have a bot bellied stove from 1880, then you may be correct. But if not....

And even short term high temps are also suppose to be coded into the flue by code. So are also okay, and within safety margins (if the flue was installed to code). That is, flue temps are only needed for the neophyte (and as a backup if you never cleaned your flue and have a chimney fire). After a while, you should "get it", and learn how to deal with your stove properly.

So the flues, if modern, already are coded into spikes in temps, etc.. Even to the extremes you mentioned.

If one is running temps at such extremes constantly, then they are doing something wrong.

And again... These were start up temps. These always get the most blasts of air, and are often a lot hotter then "constant running" temps. So you need to put that into perspective.

Hope this helps.
All that is fine and dandy if the stove is installed exactly per the recommended setup given by the manufacturer, most are not, there's a difference between meeting code, and the best install practice. My stove can hit 1600F flue temps 10 minutes after lighting, well beyond the 1400F brief forced firing my stove pipe is designed for, and into the 2100F max limit for a chimney fire, this is not caused by a chimney fire either, solely based on flue gas leaving the stove. A temperature that would never be seen on a STT gauge, a device you champion as the best and only device to use.

Sure chimneys are rated to a certain temperature, and yes can be pushed to that temperature, but it also follows that limiting high temperature thermal cycles of these components ensures longer life.

If you don't like flue temps being used for efficiency calculations then please write to the EPA, or CSA, or Intertek, or any other testing agencies that have adopted the stack loss method as the accepted methodology for confirming wood stove efficiency. Yes efficiency is determined by the design of the stove, but heat that escapes the stove and goes up the flue clearly isn't being transferred to the room, ie lost efficiency.

If you choose to run high flue temps on startup go ahead, I and many others choose to run lower flue temps on startup to ensure more of our hard work (in the form of firewood) goes into our homes as heat.

I fail to see the short comings in this how-to article by @begreen that you are pointing out. I think the majority of members on this forum, and stove manufacturers alike, will agree that this article provides safe and proven guidance on the operation of a wood stove.
 

begreen

Mooderator
Staff member
Nov 18, 2005
87,319
South Puget Sound, WA
The point of the posting is education. It is specific to startups (that's in the title). Not everyone is familiar with stove burning. Many have no reference to what is normal. Yes, modern flue systems can take high temp, but sustained, repeated runs at high temp will degrade the system quicker and solely using the stovetop temperature can lead to a major increase in emissions and inefficiency due to wasted fuel. Keeping flue temps within reason reduces fuel waste, meaning more heat reserved for the house and a longer burn time. Stovetop temperature is a lagging indicator. There's no point in wasting fuel.