How to Calibrate
Your Oven Temperature
(It's not as hard as you think!)
It's November, and with
all the cooking going on this time of year, I usually find myself calibrating
lots of ovens this month. 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 in your near future, and this can be
panic time! You need to be sure
how long to cook chicken or a Thanksgiving turkey in the oven
safely. So let's talk just a bit about oven temperature.
First, even though
controls can be adjusted up or down a bit, they rarely need it,
so I'll focus mainly on older 'analog', or 'hydraulic' thermostats
here. If it has a rotary knob and no digital display, this
If the temperature's 'off' in
your electronic control oven , check your owner's manual or contact your local pro.
There are so many different adjustment procedures for these,
depending on brand and model, 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 in 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
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* temp 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 to 345F,
because it's better to put your food back into the oven for a few
minutes if under - done than using the smoke alarm to tell you when
dinner's ready (when I cook, that's my method).
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 is 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
The best way to read this
accurately is with a remote - reading thermometer. These days,
digital ones are inexpensive (way less than a pro's service
call!), and one will last you a *long* time. I used my old
Maytag unit for nearly 20 years before it bit the dust, 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
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 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
cycles more to verify that it's right. Just 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. I
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 the oven control for you. I 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.
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Many Thanks! - Dave
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