What is this stove thermo vendor talking about?

[ADK_XJ]

Against my better judgement I bought a $9 Vulcan brand magnetic stove thermo from a secondary vendor on Amazon. Price was right but didn't know much else about it. I received it today and tested it on multiple spots showing well over 100F variance from my IR gun and even up to 200F in some spots.

I wrote the vendor asking for a return and stating the lack of accuracy, this is what if to back. What is this guy even talking about?

"If you want accuracy I would not use an IR gun or a stove thermometer.

When you say degrees I guess you mean Fahrenheit. 100F seems like quite a big difference. But the stove thermometers can be easily be out by 20C depending on the temperature you are running. Often they will be more accurate but I would assume at least 10C +/-

I assume you are using an IR gun that you can change the emissivity? The IR guns are typically 2% +/- assuming the emissivity is setup correct. Otherwise it can be way out.

Assuming emissivity not set up on the IR gun then 100F difference very likely."

 

[mopar440_6]

Non-contact IR thermometers operate by measuring the emitted infrared energy from an object. Different materials and surface finishes will have different rates of emission (emissivity) based on how much energy the object is actually giving off and how much energy is being reflected. The range of emissivity is 0 to 1.0. Some of the higher end IR thermometers have adjustable emissivity ranges so that the user can adjust it to the expected emissivity of the object for a more accurate reading. That said, most IR thermos are set to 0.95 emissivity as the default. The emissivity of flat black paint is generally between 0.90-0.98. So, assuming you don't have gold leaf covering the front of your stove, you should be extremely close. 2% accuracy for the IR would only be +/-12*F at 600*F which is FAR from the +/-20*C (68*F) variance the metal spring thermometers can show.

Below is a very good tech document explaining how IR thermometers work and how to calibrate your emissivity if you have that feature.
(broken link removed to http://www.tnp-instruments.com/sitebuildercontent/sitebuilderfiles/Infrared%20Thermometer%20and%20Emissivity.pdf)
(broken link removed to http://www.tnp-instruments.com/sitebuildercontent/sitebuilderfiles/Infrared%20Thermometer%20and%20Emissivity.pdf)

Based on the seller's email he essentially confirmed everything you're seeing. My opinion is that the seller is trying to confuse you and just get you to say "ok, guess that's just how it is." I would push VERY hard that you either need a replacement unit or a full refund. But, be warned none of the stove thermometers (+/-12%) will be half as accurate as your IR (+/-2%).

 

[CountryBoy19]

To add on to what was said above, if your stove is, in fact, flat black then you don't have to tell him your IR thermo doesn't allow emissivity changes, just tell him the emissivity is set correctly for the surface you're measuring on.

Of course, if you're measuring on stainless flue-pipe or glass etc the emissivity should be set much lower than that of flat-black. If it's not set right you'll get readings lower than the actual temperature when using your IR thermo.

 

[xman23]

The bimetal ones have worked for years well with decent accuracy. They do need some time at a location before they read the temp. The stove will have different temperatures at different locations. Not that I need them much, just recalling what the burn has been for the last few hours and the current fire looks like and I can guess what the stove top temp is. That said, if you need heat that requires running the stove at close to its maximum, get something that allows you to monitor it.

 

[ADK_XJ]

Thanks for the input, all. I work with Salespeople enough to see through the "look over here" tactic of his explanation but the actual science behind it really helps. Yes, I am unfortunately not in a position to have a gold leaf stove body - heh - so I've found my IR gun to be a very good measurement of the temperature : performance guidelines I've read about here.

The biggest issue is that this thermo is not even close or providing a relative range of temperatures that I could judge performance from at a glance from across the room. I'm returning this unit and snagging an Inferno.

 

[maple1]

Are the temp readings on the magnetic guage erratic, or consistently off?

If consistently off, it would still likely be useful, as long as you know how much it's off. For the price, I would hang onto it and get the other one you're getting - then compare them. Might be interesting results.

Also, magnetic guages can give misleading results depending what they are used for. I have one, stuck on my flue pipe just outside the back of my boiler. I also have a probe dial type stuck in the pipe right beside it. The dial reads 100c higher than the magnetic when I'm burning. If I was to go by the magnetic, I would be thinking my flue temps were way too cool, and if I were to burn based on what the magnetic guage said I should be at, I would be overfiring. Could be pretty dangerous in the wrong situation.

 

[ADK_XJ]

Are the temp readings on the magnetic guage erratic, or consistently off?

If consistently off, it would still likely be useful, as long as you know how much it's off. For the price, I would hang onto it and get the other one you're getting - then compare them. Might be interesting results.

Also, magnetic guages can give misleading results depending what they are used for. I have one, stuck on my flue pipe just outside the back of my boiler. I also have a probe dial type stuck in the pipe right beside it. The dial reads 100c higher than the magnetic when I'm burning. If I was to go by the magnetic, I would be thinking my flue temps were way too cool, and if I were to burn based on what the magnetic guage said I should be at, I would be overfiring. Could be pretty dangerous in the wrong situation.

It is not consistent in how far the temps are off and, almost worse, it appears to get stuck around the 300-350F range and stay there overnight until I pull it off the cold stove in the morning. We'll give this inferno a try and then I may simply have to accept that I'll be bending over with an IR gun in hand for the foreseeable future.

 

[maple1]

OK - that's a different thing than. Sounds like the typical piece of crap that Neil Young was on about.

 

[mopar440_6]

...We'll give this inferno a try and then I may simply have to accept that I'll be bending over with an IR gun in hand for the foreseeable future.

You don't necessarily have to use the IR gun forever, if you're willing to spend the money. Auber makes some nice digital, thermocouple based thermometer units. They are expensive but a thermocouple is about as accurate as you're going to get and you can set high and low alarms. They have options for washer mount, probe type, and magnetic mount thermocouples.

Base model: http://www.auberins.com/index.php?main_page=product_info&cPath=17&products_id=292

Wireless (2nd display): http://www.auberins.com/index.php?main_page=product_info&cPath=17&products_id=441

Since I have a basement install, I'm planning to get the wireless package and add an additional unit so that I can monitor both the flue gas temp (with a probe) and the stovetop (magnetic) from anywhere in the rest of the house. Just another option to think about...

 

[CountryBoy19]

You don't necessarily have to use the IR gun forever, if you're willing to spend the money. Auber makes some nice digital, thermocouple based thermometer units. They are expensive but a thermocouple is about as accurate as you're going to get and you can set high and low alarms. They have options for washer mount, probe type, and magnetic mount thermocouples.

Base model: http://www.auberins.com/index.php?main_page=product_info&cPath=17&products_id=292

Wireless (2nd display): http://www.auberins.com/index.php?main_page=product_info&cPath=17&products_id=441

Since I have a basement install, I'm planning to get the wireless package and add an additional unit so that I can monitor both the flue gas temp (with a probe) and the stovetop (magnetic) from anywhere in the rest of the house. Just another option to think about...

I'm sure the Auber units are very nice, but for the purpose of measuring temps on a stove, the same thing can be had from ebay for a few dollars. As a matter of fact, a high-temp probe (1200 degree I think) can be had for $10-15 and added onto a $3 K-type thermocouple reader will get you what you need within a 5% or so accuracy (but with a great deal of consistency).

 

[ADK_XJ]

I'm sure the Auber units are very nice, but for the purpose of measuring temps on a stove, the same thing can be had from ebay for a few dollars. As a matter of fact, a high-temp probe (1200 degree I think) can be had for $10-15 and added onto a $3 K-type thermocouple reader will get you what you need within a 5% or so accuracy (but with a great deal of consistency).

Go on...

But, really, is that something I can just assemble from said parts and get into a masonry surrounded insert install?

 

[mopar440_6]

I'm sure the Auber units are very nice, but for the purpose of measuring temps on a stove, the same thing can be had from ebay for a few dollars. As a matter of fact, a high-temp probe (1200 degree I think) can be had for $10-15 and added onto a $3 K-type thermocouple reader will get you what you need within a 5% or so accuracy (but with a great deal of consistency).

My only issue with any type of cheap K-type thermometer (I have never seen a $3 unit, usually $20 and up), is that they all operate on batteries and have automatic shutoffs. Right now I'm using a Fluke 52 thermometer which is extremely accurate (I'm a test engineer and I get it calibrated at work) but it's also battery powered and shuts off after 15 minutes. If I'm going to get up and walk over to the stove to turn the thermometer back on, I'll just use my IR gun. The Auber units are powered by a wall socket and will display the temperature at all times. I want to be able to read my temps from across the room.

That said, you are correct in that 5% accuracy is more than adequate for stove temperatures and I'm not one to spend money I don't have to. I've been looking for a dual input, dual display, AC powered thermocouple display and have not come up with anything. Please provide more information on these $3 thermocouple readers.

 

[CountryBoy19]

Go on...
But, really, is that something I can just assemble from said parts and get into a masonry surrounded insert install?

Yes, you can do this quite easily... As noted below the unit I was talking about is battery powered, in that case it's as easy as place thermocouple where you want to measure temp, route wire to location of reader unit, plug wire into unit.

I've been looking for a dual input, dual display, AC powered thermocouple display and have not come up with anything. Please provide more information on these $3 thermocouple readers.

I completely overlooked that part. I'll have to check my cheapo $3 unit to see if it has auto-off. It is battery powered, but I'm not sure if it turns off automatically or not. I've had it for several years now and I haven't had to replace the battery yet. As long as it doesn't power off automatically, for a battery powered unit you can find a "wall-wart" at your local goodwill that will provide the correct input voltage, open up the battery compartment and solder the wires onto the battery terminals and you now have a plug-in unit.