How to Calibrate Your Oven Temperature
(It's not as hard as you think!)

(This article originally appeared in the November 2004 issue of the free email newsletter I call The DRSNews. You ARE subscribed, right?)

It's November, and I always find myself calibrating a lot of ovens this time of year, with Thanksgiving and Christmas closing in. 

That oven that's been a little too hot or that you've had to set 50 degrees higher needs to be *right* for all the baking you see in your near future, and this can be panic time! So I thought this night be a good time to go over a couple of the basics of oven temp's. 

First, even though electronic controls can be adjusted up or down a bit, they rarely need it, so I'll focus mainly on 'analog', or 'hydraulic' thermostats here. If it has a rotary knob and no digital display, this describes yours. 

If the temperature's 'off' in your electronic control oven , I'd contact your local pro, as there are so many different adjustment procedures for these, depending on brand, there's not space here to get into them.

We will be talking a bit about the various error ('F') codes in the electronic range controls next month, though.

Contrary to popular opinion, when you set your oven temp to 350F, it doesn't heat to 350F and *stay* there. (In a perfect world, it would, but in this old fallen one, it just doesn't work that way <grin>). 

An oven 'ramps up' in preheat - usually 5 to 10 minutes - to a temp that's usually well above the 'set' temp. At 350, for example, you'll see the average electric oven heat to around 400F before cycling off the first time. 

After preheat, the average 'differential', or range of temp's between on and off, will vary from one oven to another. But a 50 degree F differential is considered very accurate, and even electronic controls don't get much better than this in the real world. 

So what we want at the 350 setting is an *average* of around 350 or a little less. Ideally, this is an 'on' temp of around 325F and back 'off' at around 375F, yielding an average of 350. Setting this a bit lower than 350F isn't a bad idea, though. I usually aim for an average of 340F or 345F, because it's easier to put your food back into the oven for a few minutes if under - done than it is opening the door to find a 'burnt offering'. 

OK, so now we know what to 'shoot for', so how do we measure the actual oven temperature? Well, let me answer that by telling you how *not* to try it. Don't rely on those $2.99 dial - type thermometers from the local grocery or hardware store. They're never very accurate, and it's pretty much impossible to get a good idea what's going on inside the oven using one. 

One note that I'll insert here, before you start: check the position of the thermostat's sensing bulb inside the oven. Make sure it's fastened securely in its mounting, usually with two small steel clips, and is *not touching the oven wall*. This is very important. 

The t'stat senses air temperature, and if its sensing bulb's touching metal, the accuracy will be severely 'off' - usually averaging very low (electronic sensors are mounted more securely, but it pays to take a quick look at one of those before you start, too, just to be sure).

The best way to read this accurately is with a remote - reading thermometer. These days, digital ones are very inexpensive (much less than a pro's service call!), and one will last you a *long* time. I've had my old Maytag unit for nearly 20 years (!), and use it several  times per week, at least. 

Way back when I bought it, cost was around $70, but these days you'll often see temperature capability built into inexpensive digital volt-ohm meters. Radio Shack sells them at very reasonable cost, as do other retailers, and they work very well. Usually accurate to within *one degree F*, which is more than enough accuracy for our purposes here. 

When testing, place the end of the meter's thermocouple in the center of the oven - I usually twist it around the center of a rack - and you watch the temp change up and down with the door closed. 

Allow about an hour to run at least 3 on/off 'cycles' up and down, then adjust, and run 2 or 3 more to verify that it's right. 

Write down the 'on' and 'off' temps for several cycles, and divide the difference between the two to get the current average.

Adjustment procedures vary widely between brands and models, but often you'll see a pair of screws on the back of the tstat  knob, and by loosening these the indicator can be rotated to the correct setting, matching the *average* on your meter. 

If your tstat knob has no screws, you'll commonly see a tiny screw inside the tstat shaft, and this is turned a bit to change setting. 

On most of these, turning that little screw CW lowers temp, CCW raises it. The 'trick' is finding (or grinding down) a screwdriver small enough to fit. We used to buy them from our parts distributors, but I've had trouble finding them the last few years, so have had to carefully grind small 'pocket' screwdrivers down to fit. 

If you can't get enough adjustment to bring your oven temp into line using the available range on the knob or with that little screw (or if the screw's 'frozen' - not uncommon), you'll have to 'bite the bullet' and replace either the tstat or the range, I'm afraid. 

If it should come to that, drop me an email with your model number and I'll be happy to research one for you. We have some pretty good parts sources, and I can get parts to you pretty fast. I get a 'kick' out of helping handy folks, especially when they realize that they actually *can* do way more in this area than they previously thought.

Copyright 2004 www.DavesRepair.com 
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