"sdwebguy" > wrote in message
ups.com...
> When we bought our house, the home inspector said the oven temperature
> was hot +25 degrees. We never thought of testing it ourselves since it
> was just tested -- but recently, we called the home warranty before it
> expired and had it tested again. He said it was accurate (not too hot).
> He said we can test it ourselves by buying an oven thermometer, and
> that we should be sure to buy a mercury one because it is more accurate
> (suggesting that the inspector did not have a mercury-based one).
>
> First, I didnt know thermometers could NOT work without mercury -- I
> never see thermometers advertised as "mercury-based' or otherwise.
>
> So what do you suggest for testing the oven temp? We were left with the
> feeling of having to prove the home warranty guy wrong.

Where you put the thermometer in the chamber, and with what, will vary the
reading. The temperature at the front will be different than near the back,
the temperature along the walls different than in the middle, and the
temperature near the top different than near the bottom.

So to check the oven itself, one puts the thermometer near the middle of
the middle rack in an empty oven.
To check how the oven bakes the particular food, one puts the thermometer
near the food you are baking. (FWIW, the oven does not bake things at the
exact middle of the chamber - that space is almost always taken up by food,
preventing air from ever being at the dead middle)

You could measure the temperature to a tenth of a degree - but why? The
food needs heat to cook vis-a-vis temperature, and a few degrees one way or
the other in the air temperature of the oven is not nearly as significant as
other parameters food preparation, ore even of the oven.
The metal coil type thermometers are bascially averaging
devices -averaging measurement devices are designed to be slow to respond
because they measure the average temperature across a period of time.
Instant measuring devices measure at a point in time, and are thus much
faster - but for measuring an average oven temperature with one of these,
you need to take several readings across a relatively long period of time
and chart the temperatures.

Note that temperature is only the measure of the difference necessary
for convection heat transfer.
(E.g., a bad coil can give you proper temperature on an emepoty oven in
preheat mode but it can't give you enough heat to sustain that temperature
in the chamber containing cold food for several hours - so with a weak coil,
you put the food in a proper-temp oven, the temp drops as it heats up the
food and the coil then runs steady trying to hold temperature as the
temperature slowly drops, and somewhere along the cooking process, the food
is hot enough to allow the oven to finally catch up.)

------

Basics - Non-microwave ovens use convection and radiation to heat the food
when roasting and baking.

Non-microwave ovens can be natural air convection or powered air convection.
Fans that circulate enough air so as to "scrub" the food with air, e.g.,
"convection ovens", reduce the variation of temperature in the chamber vs.
natural convection ovens (as well as speed up convection-mode heat
transfer).
Temperature is used to create a heat flow. Heat flow is created by having
air moving across coils or in heat "chutes" at the rear of the oven, and
then carrying that heat in the air to the food and transferring it by moving
heated air across the food.

The heated walls will radiate heat, radiation which aids in heating
anything of a lower temperature inside the chamber. (In broiler mode,
radiation is the primary heating mechanism.)
It takes longer for the walls to reach temperature than it does for the
air in the chamber to heat.

1) heat transfer law requires differences in the oven for it to work. Air
moves heat from the hot coils/flame pan to the cool food. Thus by the laws
of thermodynamics, a natural convection oven that works cannot have a
perfectly even temperature.

2) The gradient - The oven's temperature varies inside the chamber even when
empty: it is hotter at the coils than is the average temperature of the air;
it is hotter near the top than near the bottom; the air is hotter just above
the flame pan/coils than along the edges.
And it varies from the initial placing of the food to the final moments in
the oven, since the food heats and that change in food temperature changes
the natrual convection currents in the oven (e.g., a 300 degree cookie in a
300 degree oven results in no heat transfer, meaning the only convection
current left is from the coils to the chamber walls.)

3) Oven convection currents and size - The food and pan interaction with the
air varies with the physical size of the oven chamber - the temperature
distribution in a 30 inch oven is generally more even than it is when baking
and roasting the same item in a 24 inch oven.

4) Oven temperature controls - Oven temperature is not steady in a "brand
new perfect oven" - it varies from the "on" set point of the thermostat/oven
temp controller (jewel lite on) at the upper end, to the "off" set point of
the thermostat/oven temp controller.

5) Food does not require a "perfect temperature" to bake/roast. The
"allowed variation" depends on chamber size, wattage size, wall cleanliness,
and several parameters of the food item being prepared.

So basically, you are moving heat into varing types and shapes and masses
and heat capacities of food, using a device which is designed to vary, using
a device which must vary by the laws of physics to work - in a chamber that
always creates different variations in gradient that vary during the cooking
process.

The art of cooking....

there are a few more parameters, and there is more detail for each of these,
but you get the idea....

fwiw

>
> Thanks for any tips,
> Tim
>