Magnetic thermometer way off

[AbrK]

I bought a IR thermometer yesterday. My magnetic thermometer on the stove says it’s 500F and the IR says it’s 381F that’s a big difference in temperature


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[bholler]

Magnetic thermometers are not terribly accurate but cheap ir thermometers are not either.

 

[AbrK]

The Ir gun was on sale at Canadian Tire for 20 bucks regularly a 100 bucks so not that cheap just seem weird that’s it’s like a 115 Degrees off I could see 20 or 50 being more acceptable


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[Squisher]

Disappointing for sure. Did you try all around the magnetic to see? You are reading the pipe around it with the IR right? Not the magnetic thermometer itself?

Do you have any other thermometers/references you can compare to?

 

[AbrK]

Yea I was reading all around the thermometer with the IR gun not the thermometer itself and no I don’t have any thermometers to compare it to I’m gjnna head over to my fathers later on and measure his pipe around his thermometer and see what that says cause either my IR gun is messed up or my magnetic one is something isn’t adding up lol. on the plus side apparently I’ve been running my stove on the cooler side and it’s been cooking us out of the house so I known she will definitely pump the heat out in the cold weather. I’ll be checking my chimney this week for creasote as I’ve clearly been burning the stove a little cool.


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[RobbieB]

I had a magnetic one an "Inferno" that used to get its coil spring stuck and was way off because of that. Replaced with a Rutland and that works better.

 

[Squisher]

Unless the IR is wrong.

I have 2-3 different brands of magnetic thermometers(no sbi one though), a ring thermocouple to digital readout and a ryobi IR gun. They have all been very close when I've compared. So yes, something is off with one of yours.

I will look forward to hearing the results of your further investigation. Being in Canada too I have often referred people to CT to pick up a IR gun on sale just as you did.

 

[AbrK]

So went to my fathers and his is only about 15-20 degrees off. When the thermometer on my stove is at 300 it seems to be about 50 degrees off and as it gets hotter it becomes more out of wack for whatever reason.


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[Earlnemo]

Trust nothing and no one. There is no objective truth in 2022.

 

[Earlnemo]

Magnetic thermometers are not terribly accurate but cheap ir thermometers are not either.

Huh. Further research in the archives here produced this:

What gives? As you can see from my original pic, all three magnets disagree, but the Thermpro IR agree with the Rutland. Who to trust?

 

[appointed EPA deviant]

Silly thought just occurred to me, could an IR thermometer reading off of boiling water show if it is accurate?

 

[Earlnemo]

User "tjnamtiw" seems to not be here anymore, but makes reference to certain material types giving spurious readings. The instruction booklet for this IR gun refers to this as the "emissivity" of the material type being measured. I had to call the manufacturer to get a clear understanding of this, but essentially the IR gun I bought can be set to the emmissivity rate of different types. I wish I had done this step before posting my first picture because the IR gun now strongly disagrees with the Rutland and is much closer to the Chimgard & Galafire.

 

[begreen]

LOL. The Rutland is not way off. My guess is that if a temperature reading is done on other spots close to it, maybe to the left of it, that it could be close. The Condar is a flue thermometer. If the stovepipe is single-wall, try placing it about 18" above the stove and see how it reads there in comparison to the IR reading.

Here is what I get on our 32 yr old. SandHill thermometer. They don't make them like they used to.

 

[Eman85]

Man with one watch knows what time it is, man with 2 can only guess.

 

[begreen]

User "tjnamtiw" seems to not be here anymore, but makes reference to certain material types giving spurious readings. The instruction booklet for this IR gun refers to this as the "emissivity" of the material type being measured. I had to call the manufacturer to get a clear understanding of this, but essentially the IR gun I bought can be set to the emmissivity rate of different types. I wish I had done this step before posting my first picture because the IR gun now strongly disagrees with the Rutland and is much closer to the Chimgard & Galafire.

The default of .95 should be pretty close to the stovetop emissivity. I see the black stove top as asphalt or carbon equivalent.

 

[Earlnemo]

The default of .95 should be pretty close to the stove top emissivity.

The default was indeed .95. The chart provided say the iron should be set at .70 , and dude on the phone confirmed this. I attached their chart in post above.

 

[begreen]

But the cast iron is painted black. Did you tell them that?

 

[marty319]

Silly thought just occurred to me, could an IR thermometer reading off of boiling water show if it is accurate?

I bought a cheapo IRfrom ebay,Chinese of course, tried to measure boiling water numerous times,about 20° low on IR

 

[Earlnemo]

But the cast iron is painted black. Did you tell them that?

The griddle isn't painted, is it? I did play with that idea and take measurements from griddle surface and then 1/2" away on rough cast surface. There was a slight difference.

And begreen - the flue thermometer has different markings for what is considered "cool" and "overfire", but still is just measuring temp, right. And it is a hearth install, just a short steel collar connecting the flexible insulated liner to the cast collar of the stove. Can't get flue temp.

 

[begreen]

The griddle isn't painted, is it?

The spot where the red dot of the laser is pointed looks much blacker in the first picture. What readings show up if it's set to .95 and read off the painted parts of the stove? How does this compare with the thermometers placed there?

the flue thermometer has different markings for what is considered "cool" and "overfire", but still is just measuring temp, right.

You may be right. I'm not sure if there is a calibration design difference, that's why I asked. The folks at Condar should know. If the stovepipe is single-wall, it seems like an interesting test.

 

[armanidog]

Set your oven to 350F and see what the thermometer says while sitting in the oven (the thermometer, not you) .

 

[Earlnemo]

Set your oven to 350F and see what the thermometer says while sitting in the oven (the thermometer, not you) .

Heh. We had to buy a fancy baking thermometer that hangs off the oven rack because wife said the temps on the dial were not accurate. Again, which to trust? I did consider boiling a metal spoon in water and then measuring that (212).

 

[zak77]

I have a Rutland magnetic on my flue but it typically reads 200° less than the flue temp measured by an IR gun. Some people have good luck with them and others do not.