Woodstove thermometer accuracy

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Rogerwood

New Member
Jan 7, 2021
38
Kansas
I wonder just how much I should be concerned about my thermometer readings. I have a Rutland burn indicator on the top front of my 2004 Lopi liberty stove and a Flueguard Probe 18 inches up in my double wall flue pipe.
According to my flue pipe thermometer I should be running my stove cooler, but according to my stove indicator, which I know isn’t completely accurate since it’s just on the top of my stove, I should be running my stove hotter. According to my house temperature I need to be running my stove hotter.
what do you all recommend? I’m trying to heat my house with just wood, but I don’t wanna get to the point where I burn it down. I’m also considering adding a damper to my flue pipe to help hold more heat in my woodstove. Would that be OK with a Lopi Liberty?
Here are some pictures of what the two different thermometers say at the same time:

096D98F4-34C1-4938-AE80-5DA45B6B97FC.jpeg 9D43981E-D7D0-4856-AEDC-512E643EA21B.jpeg
 

Rogerwood

New Member
Jan 7, 2021
38
Kansas
Here are the readings After readjusting the air mix a couple of times
 

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Highbeam

Minister of Fire
Dec 28, 2006
19,153
Mt. Rainier Foothills, WA
Is that single wall pipe? It must be since you are using a surface meter. With screws above the seams it may be upside down.
 

MongoMongoson

Member
Feb 6, 2021
162
Wisconsin
I like to use an IR temperature gun for the stove top. I have found that the magnetic dial is pretty slow to respond.

I have a probe like yours, but I don't know the accuracy of it. I expect that it is not very accurate. I am in the process of upgrading to a thermocouple probe.

That being said, having the flue probe in the red makes me nervous. With a newly swept flue, 1000 would not scare me too much but I would do whatever I could to bring it down. If it had been a couple of months since I had swept, 1000 would make me pretty nervous. That is right about the temperature where creosote can light up.

Seems like you would have to have a lot of air flow through the stove to have your flue that hot while keeping the stove top relatively cool... something like a fireplace with unrestricted air inlet and lots of fuel. You do have door gaskets and a door installed, right? With that much heat going up the pipe, you are heating the outdoors more than your house.
 

Woodsplitter67

Minister of Fire
Jan 19, 2017
1,959
Woolwich nj
The bimetal thermometers are inaccurate. I have 2 on mine also.. I use an IR gun now. If my bimetal says the STT is 500...its actually 650 on the Ir gun. I know I need.to close up the damper before 500 on the bimetal.. The IR gun is cheap enough and it's more accurate...
 
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Highbeam

Minister of Fire
Dec 28, 2006
19,153
Mt. Rainier Foothills, WA
I found my 10+ year old flueguard by condar probe meter to be pretty dang accurate. Same with my condar surface meters unless the blowers are on and blowing air at the bimetallic coil which cools it and lowers the reading.

On my hearthstone I could wrap that flue meter up to 1250 easy. Some stoves puke a lot more heat up the flue than others.

C08D00EE-93D3-43A2-AEC6-D5CE523F26A3.jpeg A6E6273D-41DF-42A8-A74A-5AF9AC2F688B.jpeg
 

Rogerwood

New Member
Jan 7, 2021
38
Kansas
I like to use an IR temperature gun for the stove top. I have found that the magnetic dial is pretty slow to respond.

I have a probe like yours, but I don't know the accuracy of it. I expect that it is not very accurate. I am in the process of upgrading to a thermocouple probe.

That being said, having the flue probe in the red makes me nervous. With a newly swept flue, 1000 would not scare me too much but I would do whatever I could to bring it down. If it had been a couple of months since I had swept, 1000 would make me pretty nervous. That is right about the temperature where creosote can light up.

Seems like you would have to have a lot of air flow through the stove to have your flue that hot while keeping the stove top relatively cool... something like a fireplace with unrestricted air inlet and lots of fuel. You do have door gaskets and a door installed, right? With that much heat going up the pipe, you are heating the outdoors more than your house.
I do have a good door and decent door gasket. I think I have a really good draw on my flu because of where the pipe exits the house. That’s why I wonder if a damper would help in slowing down the draft so I’m not throwing so much heat out side

FFE4D000-CD61-43E4-8D6B-A43F50C092F6.jpeg
 

kennyp2339

Minister of Fire
Feb 16, 2014
5,937
07462
@Rogerwood your 2004 lopi has an efficiency of 70% under the most perfect conditions. A few tests can be done to determine if your draft is above the recommended value of between .05 - .08"wc
First is once the fire gets cruising, when you turn your air adjustment all the way down, does the main seat of the fire decrease? (not secondary's) If you can adjust your air with noticeable results within 10min of adjustment then I would think your draft is close to within spec.
Another thing to do is to buy a manometer and test your draft were the flue probe thermometer is, that will give you a def reading, if you have a meter, the true draft is determined while the stove is running on the high setting.
While I have a different stove, I had an excessive draft issue with my setup, on high I was running anywhere from a .15 to a .18 (especially if it was windy) My issues were excessive coal build up in the fire box, blowing through cats, burn times which I thought could be better and lack of heat (again I thought I should be extracting more heat from the stove top) I installed a damper and have been religiously keeping it closed off fully when temps are below freezing, I have experienced a night and day difference with my stove's function and performance. No more excessive coaling, lots of heat coming off the stove top w/ and w/out blower running, burns times as advertised from the manufacturer, and reduced wood consumption.
 

Woody Stover

Minister of Fire
Dec 25, 2010
12,266
Southern IN
I found my 10+ year old flueguard by condar probe meter to be pretty dang accurate. Same with my condar surface meters
I like the Condars. Ones I've tested with the IR gun were close. I've had a couple of those Rutlands that were way off, and one where the needle came loose from the stem.
 

Rogerwood

New Member
Jan 7, 2021
38
Kansas
The bimetal thermometers are inaccurate. I have 2 on mine also.. I use an IR gun now. If my bimetal says the STT is 500...its actually 650 on the Ir gun. I know I need.to close up the damper before 500 on the bimetal.. The IR gun is cheap enough and it's more accurate...
A problem I see with the infrared gun is it’s not gonna tell me what the inside of my double wall flu pipe is
 

Rogerwood

New Member
Jan 7, 2021
38
Kansas
I’ll try to install a damper this weekend and see what happens
I got the damper put in. It definitely makes a difference. My stove heats up a lot slower. But my flue thermometer was able to stay in the normal temperature range.
I did find out that my door gasket is not sealing very good. I forgot to pull out the bypass before starting a new fire. The stove filled with smoke and when I shut the door the smoke kept coming out around the door seal as well as the joints in the flue pipe.
 
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Hoytman

Feeling the Heat
Jan 6, 2020
356
Ohio
That doesn’t mean the door gasket is bad. The stove is designed for smoke to go through that by-pass upon loading. Heat is designed to go over the air tube baffle, not smoke...not enough heat yet to carry all that smoke through that path.
 

Rogerwood

New Member
Jan 7, 2021
38
Kansas
OK. Not sure if this is a fair test, but I put my Rutland and my condar thermometers as close together as possible and the temperatures are way different. Rutland says 300 while the Condar is 1300. Is it just me or is my Condar WAY OFF!

1A68630A-0419-44CE-971F-ED396C7D8F9E.jpeg 4C088EEB-CAA3-453B-860E-0F61E87B5D43.jpeg
 
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Rogerwood

New Member
Jan 7, 2021
38
Kansas
That doesn’t mean the door gasket is bad. The stove is designed for smoke to go through that by-pass upon loading. Heat is designed to go over the air tube baffle, not smoke...not enough heat yet to carry all that smoke through that path.
But if smoke can come past it when the door is shut doesn’t that also mean the air will be coming in around it when the fire is going? I thought the idea is to keep air from coming in through the door so you can control it with the main and secondary air inlets
 

Hoytman

Feeling the Heat
Jan 6, 2020
356
Ohio
To your question; not necessarily.

If the by-pass is closed upon starting a fire and you close the load door that fire will burn until all oxygen is consumed inside the firebox, then it will go out. However, most modern stoves, including your Lopi, always has some oxygen going into the box at all times even with the control lever fully closed, and feeding oxygen into the box which can allow the entire box to fill with smoke. Your gaskets are not designed to make the box entirely air tight, rather they are designed to control the amount of air allowed in.

A dollar bill test on a gasket does not have to cause a dollar bill to rip apart when pulled. If you pull on a dollar bill it should not slip free but be snug, or hard to pull out. This is enough pressure resistance at the gasket to allow air to come from predetermined air inlets rather than randomly through a gasket.

With the bypass closed upon starting a fire and the load door closed it may not be unusual for at least some smoke to escape the stove through the door gasketing. I would not think this would be an excessive amount, but I suppose that too is possible. It should cease to escape from the door area as soon as the bypass is opened especially if the air intakes are open, which they should be fully opened when starting the stove anyway.

That bypass was put there for a reason and is one of the best features of the Lopi stove. I feel many more stoves should utilize a bypass, and many more already do, yet others had it and the same newer models no longer do. An example of that would be the Drolet Myriad II & III models. The Myriad III version no longer has a bypass. These bypass’ can also double as a safety to allow excessive heat to be removed from the stove while at the same time closing the air intakes to starve the fire of oxygen. Unfortunately, this method of starving a fire of oxygen in an emergency situation cannot totally stave a fire of oxygen in most modern stoves as a result of design changes to satisfy clean burning stipulations by the EPA...which I feel is a significant safety hazard in and of itself. Older stoves could be starved of air and the fire snuffed completely out. Few stoves today allow for that but there are a few.

I also suppose it is possible simply to have a bad spot in the door gasketing in which case an inspection or dollar bill test could reveal and the gasket would need replacement. Make sure window gasketing is in good condition as well.

You can also test the gasketing by getting a good fire burning and using an incense stick around the door. If it is leaking you will see smoke being drawn into and through that area of the gasket.

I could be wrong, but I think it is a misconception that these gaskets act as a rubber gasket would completely stopping any and all air. Rather, I feel stove gaskets perform well enough to make any air infiltration or escape imperceptible. That’s my take on it anyway. I could be totally wrong. If you don’t believe me just ask my wife. LOL.
 
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Rogerwood

New Member
Jan 7, 2021
38
Kansas
Unfortunately, this method of starving a fire of oxygen in an emergency situation cannot totally stave a fire of oxygen in most modern stoves as a result of design changes to satisfy clean burning stipulations by the EPA...which I feel is a significant safety hazard in and of itself.
I definitely agree with that. There’s a few times I got my fire too hot and because I can’t completely shut the air off it took forever get the temperature back down.
I’ve been thinking about cutting out a piece of sheet metal to slip in between the slide control and the airline inlets on my woodstove to suffocate it in case future over fires
 
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Jan 29, 2021
145
VA, east central
I wonder just how much I should be concerned about my thermometer readings. I have a Rutland burn indicator on the top front of my 2004 Lopi liberty stove and a Flueguard Probe 18 inches up in my double wall flue pipe.
According to my flue pipe thermometer I should be running my stove cooler, but according to my stove indicator, which I know isn’t completely accurate since it’s just on the top of my stove, I should be running my stove hotter. According to my house temperature I need to be running my stove hotter.
what do you all recommend? I’m trying to heat my house with just wood, but I don’t wanna get to the point where I burn it down. I’m also considering adding a damper to my flue pipe to help hold more heat in my woodstove. Would that be OK with a Lopi Liberty?
Here are some pictures of what the two different thermometers say at the same time:

View attachment 275561 View attachment 275562
The Rutland that I have is off by 100+ degrees below actual at higher temps as compared to an infrared gun. It's around 50 under at lower temps. I have it mounted right above the door at the point where the top of the fire box is welded to the face plate which is pretty much the hottest part on my stove. My stove has an "air jacket" that a blower heats air by moving air between it and the firebox. If your stove has an air jacket, make sure your Rutland isn't mounted on that as it is cooler than the firebox and faceplate.
 
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Hoytman

Feeling the Heat
Jan 6, 2020
356
Ohio
I definitely agree with that. There’s a few times I got my fire too hot and because I can’t completely shut the air off it took forever get the temperature back down.
I’ve been thinking about cutting out a piece of sheet metal to slip in between the slide control and the airline inlets on my woodstove to suffocate it in case future over fires
With my Liberty, that I bought used for a song and have not used, I have considered something similar. However, rather than slipping a piece of metal in there for the same reason you stated, I’m wanting to configure it for a bi-metallic thermostat so it can self regulate the stove temperature just like a BK stove and my Hitzer coal stove. It’s not going to be as easy as it sounds though, least not controlling both primary and secondary air controls. I thought about just tying it with the secondary air. I’ll have to see though. I haven’t really taken the time to inspect the stove all that well yet. I just know there are two intakes on the bottom of the stove.
 
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Hoytman

Feeling the Heat
Jan 6, 2020
356
Ohio
My Rutland thermometers are spot in with my IR gun.

Good tip on moving them away from “jacketing” and heat exchangers where air is blown through. From those double wall stove locations and o my single wall locations the temps can vary 100*.
 

Rogerwood

New Member
Jan 7, 2021
38
Kansas
With my Liberty, that I bought used for a song and have not used, I have considered something similar. However, rather than slipping a piece of metal in there for the same reason you stated, I’m wanting to configure it for a bi-metallic thermostat so it can self regulate the stove temperature just like a BK stove and my Hitzer coal stove. It’s not going to be as easy as it sounds though, least not controlling both primary and secondary air controls. I thought about just tying it with the secondary air. I’ll have to see though. I haven’t really taken the time to inspect the stove all that well yet. I just know there are two intakes on the bottom of the stove.
I’d be interested in seeing what u come up with. Also any pics of the controls on your BK and Hitzer
 

Hoytman

Feeling the Heat
Jan 6, 2020
356
Ohio
Don’t have a BK. The principle is the same. Air feeds from the bottom for the coal and higher for wood with the BK. My stove has two load doors like old double front door stoves and there I also have two air intakes for wood burning. Not as efficient with wood...not even close to the BK with wood.
Set the dial according to the room temp you want. We use our furnace thermostat to monitor from. Chain opens and closes air flap on intake. Once set to meet desired room temp it is self regulating just like the BK.
I’m wanting to retrofit this stove with secondary air for wood and have it removable.

Haven’t tried burning much wood at all yet. I made bricks to go over the grates and to stop air flow from coming from underneath, which causes it to go through lots of wood. Secondary air tubes should help it burn wood much more cleanly and with the thermostat should allow for decently long burns.
8F019D34-C6DB-42C6-A589-E3D0A80B695E.jpeg
 
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gthomas785

Minister of Fire
Feb 8, 2020
501
Central MA
OK. Not sure if this is a fair test, but I put my Rutland and my condar thermometers as close together as possible and the temperatures are way different. Rutland says 300 while the Condar is 1300. Is it just me or is my Condar WAY OFF!

View attachment 275951 View attachment 275953
I think it's not a fair test. The flue probe is calibrated to read the temperature at the end of the probe assuming the dial is at a much cooler (close to room temp) temperature. Putting the dial that close to the stove will cause it to read high.

When I had a probe thermo installed in single wall, it would read high because of radiant heat from the pipe hitting the bimetallic coil. It's very sensitive to the installation.
 
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MR. GLO

Member
Jan 26, 2021
136
Massachusetts
I got the damper put in. It definitely makes a difference. My stove heats up a lot slower. But my flue thermometer was able to stay in the normal temperature range.
I did find out that my door gasket is not sealing very good. I forgot to pull out the bypass before starting a new fire. The stove filled with smoke and when I shut the door the smoke kept coming out around the door seal as well as the joints in the flue pipe.
to control the flue temp I either set the damper or decrease the air before it gets into the red. You will soon learn with your wood and amount of wood when to start the process or how much...Let us know your draft if you ever measure it.
 
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