Published January 1, 2011.
Which oven thermometer is reliable enough to tell you what's really going on inside your oven?
Fact: Ovens are inaccurate. Since all ovens cycle on and off to maintain temperature, even the best models will periodically deviate from the desired target by at least a few degrees throughout cooking. On top of this, we’ve found that ovens set to the same temperature can vary by as much as 90 degrees. We recommend recalibrating your oven regularly, but in the meantime a reliable oven thermometer will tell you what’s really going on.
Oven thermometers come in two styles: bulb and dial-face. We prefer dial-face brands, as we’ve found that the tinted alcohol used in bulb thermometers can get stuck, compromising accuracy. In addition to giving accurate temperature readings, an oven thermometer should be easy to read and easy to mount securely and safely out of the way. It should also be durable. (Even if an oven thermometer only costs a few bucks, you shouldn’t have to keep replacing it.) Our most recent favorite was a dial-face model that uses a bimetal coil (the different metals in the coils expand and contract at different rates when heated or cooled, moving the dial on the thermometer face). It worked fine until the numbers on the thermometer face disappeared, burned off by the heat.
Not convinced that it wasn’t our own fault for accidentally leaving it in the oven during a cleaning cycle, we bought duplicates of our favorite, the CDN Multi-Mount Oven Thermometer, and rounded up four other dial-face brands to see what each could do over the long and short haul. We used a thermocouple to read high and low oven temperatures and compared its readouts with those given by each thermometer. (Thermocouples are precise instant-read instruments used in scientific and industrial processes.) We also maneuvered pans and baking dishes in and out of the oven to gauge whether a thermometer stayed put and out of the way. Finally, we left a thermometer in every oven in the test kitchen and asked test cooks to provide feedback over six months of daily use.
Sure enough, despite our being careful not to leave thermometers in place during cleaning cycles, the numbers on our old favorite started to fade again. Other models developed fogged or discolored faces, were difficult to place in the oven or maneuver around with pans, and were off by as much as 10 degrees.
In the end, we were most impressed by the winner's easy-to-read numbers despite its small face. It can hang or stand freely on oven racks. It’s accurate, and after months of testing, its face remained clear, its numbers visible and readable.