Thermometers: accurate?

[cmcramer]

How accurate can a $12 magnetic thermometer be, and how would you know if it wasn't?

From my work experience in a brewery - where thermometers are a BIG deal - I know that thermometers are also notoriously inaccurate. Especially all metal ones...as opposed to the good old toxic glass + mercury ones. We calibrated our metal thermometers against two mercury thermometers, daily.

So if I want to run my new cat VC Encore at 650 degreees at griddle surface, but never up to 750 (per owners manual), can I trust my $2000 stove to a $12 thermometer? Can I run it at 700 on the griddle surface and be confident that it's not really 750?

Thanks!

 

[Stevebass4]

not too sure as i just purchased a $12.00 one as well

the way i see it is that if i know when my stove (insert) is running great ie secondary is full of blue flames and pushing out the heat i'll use the thermometer as a guide. if it's reading say 400 but running great - that's what i'll use as my benchmark. i was also thinking of picking up one of those $30.00 infrared thermometers at habor frt as a back up

as a side note your stove will not melt at 750. just get a feel for it heck it's not like you're making a souffle where temps have to be exact

 

[VTSR5]

How accurate can a $12 magnetic thermometer be, and how would you know if it wasn't?

Calibrate at 212 degrees by immersing in boiling water. Won't hurt your $12 all metal thermometer.

I recently suspected my $12 thermometer of being off by more than 100 degrees when reading 550 degrees, so I put it in the oven and checked against a believed-to-be-good oven thermometer. It was off, so I gave it an "adjustment". Close enough!

Domestic tranquillity tip: Check with the person responsible for food preparation in your household before using the oven for unauthorized applications. Don't ask me how I know.

 

[snydley]

How accurate can a $12 magnetic thermometer be, and how would you know if it wasn't?

From my work experience in a brewery - where thermometers are a BIG deal - I know that thermometers are also notoriously inaccurate. Especially all metal ones...as opposed to the good old toxic glass + mercury ones. We calibrated our metal thermometers against two mercury thermometers, daily.

So if I want to run my new cat VC Encore at 650 degreees at griddle surface, but never up to 750 (per owners manual), can I trust my $2000 stove to a $12 thermometer? Can I run it at 700 on the griddle surface and be confident that it's not really 750?

Thanks!

You want accuracy from a $12.00 thermometer? I don't care what part of China, or what 6 year old children they have working that day it ain't gonna happen for $12.00. hh: If you want something more accurate you need a non-contact laser thermometer like the one here at Harbor Freight : http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=96451
Other manufacturers make them too, just do a search on the Internet for them.
Snyde

 

[Corey]

I would wager that they are probably 'good enough for the task at hand' With all the different stove configurations and locations that people put the thermometer, it's even hard to compare one persons stove top temp to another. The stove top is far from the hottest piece of metal in the firebox, and nothing really dramatic is going to happen until the metal hits about 1300F. Plus you've probably got 1/4 to maybe 1/2 inch between every 100 degrees, so there is not a lot of resolution there. I probably wouldn't try and brew beer with it!

 

[Ithaca]

I agree that these stove thermometers are NOT precision instruments. I have tested mine out next to a oven thermometer that goes up to 600 and they never agree. The magnetic stove is slower to respond and is usually at least 25 degrees off high or low.

So I plan on using mine as a 'broad' guide to the operation of the stove. I won't trust it to be accurate around my overfire temp (600) so I will keep it around 500 max.

Now an infrared thermometer is what I need.. Hmmm.

 

[VTSR5]

I would wager that they are probably 'good enough for the task at hand' With all the different stove configurations and locations that people put the thermometer, it's even hard to compare one persons stove top temp to another. The stove top is far from the hottest piece of metal in the firebox, and nothing really dramatic is going to happen until the metal hits about 1300F. Plus you've probably got 1/4 to maybe 1/2 inch between every 100 degrees, so there is not a lot of resolution there. I probably wouldn't try and brew beer with it!

Yeah, good enough. Not only that, they can be adjusted a little if you are careful. All I really care about is reasonable accuracy and repeatability in the range of 450 to 650 degrees, so I try to calibrate for the middle of this range, 550.

 

[ScottF]

Domestic tranquillity tip: Check with the person responsible for food preparation in your household before using the oven for unauthorized applications. Don’t ask me how I know.

VTZJ, I think I know what you mean, I once made Windsor chairs from green lumber and used the oven to kiln dry some of the pieces after they were turned. I wont ask you how you know.

 

[begreen]

For a lab accurate thermometer, you are going to pay some bucks. There are some alternatives, one being an IR digital thermometer that sells for around $40. Several members have these. Or there is a nice magnetic surface thermometer for about $90, it's the Tel-Tru DM-014-750 surface thermometer. This is the first model I’ve seen with clear black on white markings and a glass cover. That is my kind of stove thermometer. It's similar to my trusty old Sandhill, but is a polished instrument.
http://www.teltru.com/

PS: When I checked my 30 year old Sandhill with the IR thermometer it was within 5 degrees at 400 and 600 deg. So some can be relatively accurate.

 

[polaris]

How accurate can a $12 magnetic thermometer be, and how would you know if it wasn't?

From my work experience in a brewery - where thermometers are a BIG deal - I know that thermometers are also notoriously inaccurate. Especially all metal ones...as opposed to the good old toxic glass + mercury ones. We calibrated our metal thermometers against two mercury thermometers, daily.

So if I want to run my new cat VC Encore at 650 degreees at griddle surface, but never up to 750 (per owners manual), can I trust my $2000 stove to a $12 thermometer? Can I run it at 700 on the griddle surface and be confident that it's not really 750?

Thanks!

You want accuracy from a $12.00 thermometer? I don't care what part of China, or what 6 year old children they have working that day it ain't gonna happen for $12.00. hh: If you want something more accurate you need a non-contact laser thermometer like the one here at Harbor Freight : http://www.harborfreight.com/cpi/c/displayitem.taf?Itemnumber=96451
Other manufacturers make them too, just do a search on the Internet for them.
Snyde

I have a $14.00 Rutland magnetic thermometer. I also have a highly accurate laser thermometer that was not purchased from Harbor freight(purchased from the Snap on truck guy). The Rutland is within +/- 5 Degrees at all ranges. So maybe I just got lucky but I have a highly accurate magnetic thermometer(unknown country of origin) for less than $15.00.

 

[SlyFerret]

I've got a cheap magnetic thermometer. I also bought a decent laser thermometer from Harbor Freight ($40 or so). A great investment, I think.

Checking my magnetic thermometer using the laser thermometer throughout its range showed that not only is the magnetic unit inaccurate, but inaccurate by different amounts depending on temperature.

I don't really pay attention to the numbers on the magnetic thermometer, just the position of the needle. Even thought the numbers aren't accurate, the needle's movement is consistent. I know roughly when the secondary burn will kick in, roughly where it cruises, and at the low end, when to start checking the coal bed to determine how soon to reload.

-SF

 

[cmcramer]

I like the oven idea. Next time our oven is going to be heated up to 550 or so.....my $12 thermometer is gonna bake for awhile.

 

[EddyKilowatt]

I wouldn't trust the calibration on ANY of these "stove thermometers", especially the flue pipe ones that are just estimating flue temp from the pipe surface temp. And while we're at it, the infrared ("laser") units have to be calibrated for the actual surface they'll be used with (emissivity), plus field-of-view, if they're to be accurate... just because they have a digital readout doesn't make them digitally accurate.

OTOH, any and all of these thermometers can serve as useful guides for firing your stove in a repeatable and reliable way, once you learn what the "typical" readings are.

Green's right, if you really need absolute accuracy (not just relative repeatability), for example in order to keep yeast happy, then you have to invest in quality instruments, and equally, invest the time learning to make accurate measurements. The Tel-Tru outfit that he pointed out makes a nice range of thermometers and you can buy right off their website... take a look around and see what you can find. (I myself swear by their probe-type units for flue gas temperature measurements, worlds better than the ones sold through the stove trade.)

And lastly, don't sweat it too much, your stove's not going to melt if you run it 50-100 degrees too hot. If no parts are glowing when viewed in a dark room with lights off, you're probably OK in the temperature department.

Eddy

 

[hotcookcpl]

I wouldn't expect the magnetic stove thermometer to be accurate either. I just know it's "close enough". When testing your thermometers for accuracy you should probably keep in mind that oven thermometers are not very accurate either. If you really want to verify accuracy you will need something very accurate to begin with. But realisticly, how accurate does the stove thermometer have to be?

Keep warm and toasty.

 

[kenny chaos]

You guys got me thinking about my thermometer and I realized it was more than twenty years old. Bought a new one today and placed them side by side. Readings were:
Old New
300 300
350 325
400 350
500 400
550 450

 

[JotulOwner]

I was told by an "experienced wood burner" that my stovetop magnetic Rutland thermometers (yes, I have two to make sure they agree with each other) :lol: were not accurate and a flue thermometer was the only accurate measurement of temperature. Well, my cheap magnetic thermometers agree with each other (within reason), so I am not sure if a flue mounted device is necessary. Also (referring to a prior posting), I thought that the flue mounted thermometers measured flue gas temperature and not surface temperature.

 

[bsa0021]

Be careful of "Teltru" type or IR thermometers. If you drop them, they can go out of calibration... bad.
20 years in food safety taught me that.

 

[EddyKilowatt]

Also (referring to a prior posting), I thought that the flue mounted thermometers measured flue gas temperature and not surface temperature.

You'd think they would, and the Tel-Tru and other actual probe-type thermometers, with the sensing element down inside the probe, actually do.

But the "flue thermometer" I bought from a stove store, made by a company that makes lots of thermometers for the stove business, proved upon close inspection to have its bimetal coil right behind the dial face, on the *outside* of the flue pipe. I thought well okay, the probe must be copper and designed to conduct heat out to the coil... but the probe was plain solid steel (magnetic), which doesn't conduct heat well through long slim sections. When I put it in the oven the calibration was off by at least 50%.

This all led my to the view that the thing was designed to merely estimate flue temp based on surface pipe temp (or actually, on the air temp adjacent to the pipe). That's not useless; any repeatable measurement even if not absolutely accurate can be used to help fire a stove, but... for only a few bucks more you can accurately measure the *actual* flue gas temperature, unaffected by air movement in the room... and the probe type thermometers (Tel-Tru and others) have the added benefit of responding in a few seconds to changes within the firebox or stove pipe.

Eddy

 

[Brian VT]

But the "flue thermometer" I bought from a stove store, made by a company that makes lots of thermometers for the stove business, proved upon close inspection to have its bimetal coil right behind the dial face, on the *outside* of the flue pipe. I thought well okay, the probe must be copper and designed to conduct heat out to the coil... but the probe was plain solid steel (magnetic), which doesn't conduct heat well through long slim sections. When I put it in the oven the calibration was off by at least 50%.

That sounds like the Condar I just bought. Think I should I toss it and not drill through my new DVL ?
I also got a Rutland magnetic sitting on the top surface. When I got the stove into what felt like cruising mode the Rutland said 600 deg. but things didn't seem too hot to my inexperienced eye. I only had 2 splits going.
When I got down to just a few coals the Rutland said 100 deg. but I couldn't keep my hand on the top surface for more than a couple seconds.

 

[EatenByLimestone]

I use both of mine as a guide. They read the same and my nose and the temp in the room tells me if I'm running a bit hot.

Matt

 

[Redox]

Be careful of "Teltru" type or IR thermometers. If you drop them, they can go out of calibration... bad.
20 years in food safety taught me that.

Nor does running them over with a car. My $350 Raytek wasn't worth a crap after that incident... :down:

Chris

 

[cmcramer]

Got my new $30 IR thermometer........and it's the most fun I've had in a while. Did you know the surface of a cat's paw is 78 degrees F?

I also learned that my $12 Rutland magnetic thermometer is very accurate throughout its range. I did note, however, a difference
of almost 100 degrees between the center of the griddle (VC Encore Cat) and the edge of the stovetop where I had been placing my $12 thermometer for easy viewing from my upstairs vantage point. Back to the center of the griddle it goes.

Owner's manual says 700 degrees at griddle center is acceptable, but continuous 750 is not: may "damage the cast iron or enamel finish" whatever that means. I'll stick with 650 - 700 max.

And yes, my ice tea with ice cubes was exactly 31.8 degrees F. And since our well water has a high mineral content. I would expect the temperature to be a bit below 32.0. Now, about that oven temp...........................

 

[Crowbar]

Got my new $30 IR thermometer........and it's the most fun I've had in a while. Did you know the surface of a cat's paw is 78 degrees F?

I also learned that my $12 Rutland magnetic thermometer is very accurate throughout its range. I did note, however, a difference
of almost 100 degrees between the center of the griddle (VC Encore Cat) and the edge of the stovetop where I had been placing my $12 thermometer for easy viewing from my upstairs vantage point. Back to the center of the griddle it goes.

Owner's manual says 700 degrees at griddle center is acceptable, but continuous 750 is not: may "damage the cast iron or enamel finish" whatever that means. I'll stick with 650 - 700 max.

And yes, my ice tea with ice cubes was exactly 31.8 degrees F. And since our well water has a high mineral content. I would expect the temperature to be a bit below 32.0. Now, about that oven temp...........................

Sounds like fun! Imma going to go get one.

 

[Redox]

Yeah, they are definitely worth it, now that they are so cheap. Just make sure you don't point that laser at someone's eye; it will cause retinal damage. The cat loves to chase it around the room, though...

Chris

 

[Nic36]

I just bought a Rutland magnetic thermometer from Ace Hardware yesterday since I did a break-in fire last night. It's the one with the creasote/burn zone/overfire indicators. It was the last one they had, so I thought I got lucky. It seemed to work well, but I tested it in my electric oven today and it was off 100 degrees on the 500 degree oven setting. It was reading high-exactly 600 degrees F. Either my oven is way off, or the thermometer is not right. I think I am returning it.