reading flue temperature properly

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disamatic

disamatic

New Member
Aug 6, 2014
80
Gold Bar Washington
So after reading quite a bit on here about flue temperature and probes/thermocouples, when reading my flue temperature with my cheap magnetic gauge from lowes, if it says 200, can I be safe to think that the gas temp. Is 400 and I'm burning hot enough to not build creosote? Thats what I have gathered is pipe temperature is approximately 200 degrees colder than flue gas. Thanks for your thoughts.
 
This is my understanding and I could be wrong, so please correct me if I am.

Flue will be double pipe temp. So if pipe is 200, gas will be 400. If pipe is 400 gas will be 800.

The build up creosote is more a function of how efficient the firebox/fire is. Take a reading of the hottest point of your stove (the same rule of thumb applies) if your stove reads 700 the gas inside will be 1400. At that temp there will be little to no unburned gases so creosote will not build no matter what the pipe temp is
 
Too many variables to answer with certainty. First: is your stove pipe Dbl or Single wall? If it is Dbl wall your magnetic therm is about worthless - you are taking the temp of something other than the pipe carrying away your heat and is there as an insulation barrier so if it is doing what it is suppose to your not getting a true temp. For this situation a probe therm is the way to go.

Another issue addressed is creosote and that has as much or more to do with moisture in your fuel than the temp you are burning. ie: if you burned only balsa wood and newspaper for years and never reached a stove or flue temp above a 100 degrees you still would not be producing much creo - on the other hand, if all you are burning is 35% MC hardwood and get the temps to 700(eventually) you still may be at risk due to all the moisture and time it took to reach the full burn temps. Not to mention the long waiting with door cracked to get it going will eventually lead to an "oops!" moment when you get distracted.
 
I would respectfully disagree, moisture content of the wood has little to do with creosote.

Water vapor on its own is nothing more than water vapor. Water vapor doesn't create creosote on your tea kettle.

That being said, water robs the fire of heat, but if there is enough heat to overcome this there are no issues.

If you can maintain a firebox temp of around 1200-1400 degrees F. There is nothing left to create creosote.
 
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disamatic said:
So after reading quite a bit on here about flue temperature and probes/thermocouples, when reading my flue temperature with my cheap magnetic gauge from lowes, if it says 200, can I be safe to think that the gas temp. Is 400 and I'm burning hot enough to not build creosote? Thats what I have gathered is pipe temperature is approximately 200 degrees colder than flue gas. Thanks for your thoughts.
Click to expand...
It varies from 150F to 200F depending on where the temp is taken and whether there is an elbow in the pipe above the thermometer. Single wall pipe, right?
 
Randy Acton said:
I would respectfully disagree, moisture content of the wood has little to do with creosote.

Water vapor on its own is nothing more than water vapor. Water vapor doesn't create creosote on your tea kettle.

That being said, water robs the fire of heat, but if there is enough heat to overcome this there are no issues.

If you can maintain a firebox temp of around 1200-1400 degrees F. There is nothing left to create creosote.
Click to expand...

As long as the walls of the chimney are above the boiling point of water all the way up.

ETA: The particulates that create creosote are going to be going up the pipe no matter what. Your goal is for the creosote to end up on your neighbors car, not stuck to the walls of your chimney.
 
Last edited:
Yes this is standard single wall, no elbows or offsets, 6" chimney, approximately 14.5' of chimney all together, not including stove.
 
So do you folks have a recommended stove top thermometer you all like? Not looking for fancy, just something that works properly. Any thoughts? Maybe a link would be nice.
 
If it 's just for a temporary reading you can put the flue thermometer on the stovetop. Ignore the range scales and read just the temperature. Use gloves, the thermometer will be hot.
 
disamatic said:
So do you folks have a recommended stove top thermometer you all like? Not looking for fancy, just something that works properly. Any thoughts? Maybe a link would be nice.
Click to expand...

I shoot for 550 to 650 stovetop temp. Secondary combustion takes place around 1,100 degrees in the firebox and stove top temp is roughly half of the temp in the firebox. It isn't an exact science but close enough.
 
disamatic said:
So do you folks have a recommended stove top thermometer you all like? Not looking for fancy, just something that works properly. Any thoughts? Maybe a link would be nice.
Click to expand...
I like to have both a stove top and flue thermometer. I agree that the Condar thermometers are the most well liked for both. The Inferno model for stove top.
http://www.condar.com/Stovetop_Thermometers.html

Be aware that the stove top temps can vary quite a bit around the top. Like Grisu above, many of us like to have an IR "gun" thermometer that you can measure a specific spot and find the hottest places. Also useful for other measurements around the house.
 
I also have both. I think my stove top runs a little lower though, 275-400 which seems to be working for me, remember its just a scale but its pretty close. I place mine in the middle close to the pipe exit which seems to be the hottest according to the IR gun
The magnet lost its strength after the first season, guess they dont like the heat.
 
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