Barbecue Thermometer Throwdown

Three Thermometers in Question: a fancy digital probe, an old-fashioned oven model, and a grill model

When I acquired my second-hand offset smoker, the seller was quick to tell me not to trust the simple thermometer on the lid. It was fairly standard advice for most BBQ thermometers, especially ones like this that only specify if the temp is warm, ideal, or hot.

I soon learned just how untrustworthy this particular unit’s temperature gauge was when I tried to cook my first meal on it. When I had the fire built and closed up the system to start cooking, the needle on the thermometer slowly rose until it was just covering the “w” in warm. Half an hour later, after a non-stop wind blowing right through the firebox vent had whipped my coals into a raging inferno and almost all the water in my water pan had boiled off, the needle was now firmly covering the very same first letter on the dial. How’s that for sensitivity?

I thought to myself there’s got to be a better way to get a handle on this problem.

Thermometer Testing: The Water Method, Man

I had read somewhere on a BBQ site that the best way to test a thermometer was to put it in boiling water & see how it reacts. Regardless of the speed of the boil or the size of the bubbles, the laws of thermodynamics dictate that boiling water will always be 100°C/212°F at sea level – no less, no more. So, the theory behind the boiling water test is to see how close you get to the boiling point to get a handle on how accurate your thermometer is.

I have three relatively cheap thermometers I wanted to test.

The first one is a fancy digital probe meat thermometer which gave me an instant reading of 212°F when immersed in the boiling liquid and held this reading solidly for a few minutes until I removed the probe.

The second thermometer is an old-fashioned oven thermometer just like the ones recommended in Gary Wiviott’s book Low & Slow (click here to read some of my thoughts about this great tome). This particular thermometer can’t be immersed in water, so it was excluded from the test.

Thermometer number three, though, is dishwasher-safe and specially design for reading grill temperature, so I suspended the bottom in the boiling water. After a couple of minutes the needle was up in the 190-200°F range. It held this reading for the next few minutes. It was sort of accurate, but as they say, close only counts in horseshoes.

Based on the data collected in this highly unscientific study, I foolishly concluded that putting the probe through a potato and resting it on the cooking grate would be the ideal way to regulate the heat within my smoker.

The Oven Method

Well, to put it short, I found the probe to be a little unreliable during the actual cook. Then I read in Gary’s book (see above) that he only uses oven thermometers because they’re designed to give a reliable reading of ambient heat, whereas the probe is meant to give the temperature of the solid object into which it has been inserted.

It makes good sense to use the right tool for the right job, and different thermometers give different readings when used in different ways. I’ve got an infrared thermometer which is great for ascertaining the temperature of a liquid, like hot oil or boiling water, but it’s not so reliable when pointed at solid objects, such as the pans being used to heat up those liquids.

So I devised a quick test for all 3 of my thermometers using the oven in my kitchen. I decided to pre-heat my oven to 250°F, a common target temp for barbecuing, and put all three thermometers in the oven. I took readings when the oven told me it was heated up, then I waited 15 minutes and took readings again. After that, I raised the heat to 275°F, on the high side of what most consider the ideal range for BBQ, and then I took readings when the target temp was reached and then again 15 minutes later.

The downfall of this method is that it has no scientific benchmark for the accuracy of my oven’s internal thermometer, but I’ve been cooking with this particular appliance for over three years and I’ve yet to poison anyone, so I’ll take that as a sign that it’s pretty reliable.

Here are my results:

Jumped-to Conclusions

When we follow the principle of testing the thermometers in the way they’ll actually be required to operate the only unit that seems to give an accurate reading is the grill thermometer, but only after it has been given sufficient time to adjust itself. The allegedly spot-on accuracy of the probe seems to fall short when using it to gauge ambient heat, and the good old-fashioned oven thermometer, even though brand spanking new and right out of the package proved to be horribly inaccurate and erred on the high side once given adequate time to heat up.

Other Considerations

Now that I know which thermometer is the most accurate for reading ambient heat, I also have to consider things like:

• Placement:
  The heat varies considerably in an offset smoker. The same thermometer will give different readings when it’s near the firebox, beside the cooking meat, tucked in behind a water pan, or by the chimney.
• Consistency:
  Whenever you open the cooker just to look at the thermometer you will lose heat and add to your eventual cook time.

In the end, I think the best heat gauge is going to be something not inside the smoker. I’m not talking about replacing the faulty lid thermometer, though. Quite frankly, I’ve grown accustomed to it and it makes me laugh.

No, I think the best solution will be learning through trial and error by observing how the unit operates while in use. Just as we watch the exhaust to see the quality of the smoke being produced by a cooker, we can also observe things like the amount of exhaust coming out to get an idea of how fast the fuel is burning through.

Another great no-gadget approach is to learn to feel the heat of your cooker’s exhaust when it’s in the zone. When my smoker seems to be running well, I can hold the palm of my hand an inch or two over the wide-open exhaust on the side of my offset smoker for about 10 seconds before being compelled to pull my hand away (if you’re playing along at home, always remember to pull your hand away when you feel that compulsion or you will get burned). I haven’t got an exact time on that just yet, but as I build a bigger ash pile, count Mississippis in my head and acclimate my hand to being held over a hot exhaust port I hope to eventually get it down to a rather artful science.