hi folks,

had a question about how temperature is controlled in a gas oven.
till now i used to think that the dial(marked in degrees celcius)
regulates the amount of gas that can reach the oven. however i noticed
that along the insides are are two copper tubes which are closed at
one end. my guess is that they have something to do with temperature.
anyone know how this works?

thanks,
Sam

On Tue, 3 Nov 2003, Sam wrote:

> hi folks,
>
> had a question about how temperature is controlled in a gas oven.
> till now i used to think that the dial(marked in degrees celcius)
> regulates the amount of gas that can reach the oven. however i noticed
> that along the insides are are two copper tubes which are closed at
> one end. my guess is that they have something to do with temperature.
> anyone know how this works?

I'm not sure if this is true for all gas ovens but all the ovens I have
used (or installed) there is a thermostat in the oven. It has a
sensitivity range. Let's say it is 5 degrees. If I set the temperature to
350 degrees the gas will turn on until the oven reachs 355 degrees. At
that point the gas will turn off. When the temperature drops to 345
degrees the gas will turn on again.

You'll know this is how your oven works if you just turn it on and listen.
Once the oven is at temperature you will hear the burners turn off (or
reduce notably). If you open the oven door for a few minutes (maybe only
seconds) you will hear the burners kick in again.

Regulating the flow of gas would not work. Impurities in natural gas mean
it does not always burn smoothly. Some gas is cleaner than other. The
purity of your gas supply could alter from day to day. It will definitely
alter from location to location.

Things to note when buying an oven, how well does it hold the heat (better
means less burner on/off) and how sensitive is the thermostat.

--
Send e-mail to: darrell at cs dot toronto dot edu
Don't send e-mail to

(Darrell Grainger) writes:

>Newsgroups: rec.food.baking
>From: (Darrell Grainger)
>Subject: temperature control inside gas oven?
>Date: 4 Nov 2003 17:44:35 GMT
>
>On Tue, 3 Nov 2003, Sam wrote:
>>
>> had a question about how temperature is controlled in a gas oven.
>
>I'm not sure if this is true for all gas ovens but all the ovens I have
>used (or installed) there is a thermostat in the oven. It has a
>sensitivity range. Let's say it is 5 degrees. If I set the temperature to
>350 degrees the gas will turn on until the oven reachs 355 degrees. At
>that point the gas will turn off. When the temperature drops to 345
>degrees the gas will turn on again.

That's about right. Older gas ovens use mechanical thermostats. Back
in the 1950s, even stoves with automatic pilot lights for the cooktop
burners required manually lighting the oven with a match. Then a
mechanical thermostat would moderate the amount of gas from low to
high, never fully extinguishing the flame.

Most, if not all, gas stoves sold today use electronic ignition. This
conserves energy because there is not a pilot light flame burning
24-hours a day. Cooktop ignition systems are usually electronic
spark devices.

However, it's in the oven where there have been some important changes
in design -- notably for reasons of safety.

Ovens with electronic ignitors may use a very hot quartz lamp or other
device to start the oven burner. When you turn on the oven, this
lamp comes on and there is a small flow of gas to a pilot burner near
the lamp. Not until this gas ignites will the control system allow
a the flow of gas to the main oven burner. The control system
then cycles the oven pretty much as described by Darell in his response
above. The key safety feature here is that gas will not flow to the
oven burner until the ignitor comes on and the pilot flame is proven.

Mechanical oven thermostats are notoriously inaccurate. Electronic
thermostats, some with multiple temperature sensors, are able to control
the oven temperature more accurately and within a much narrower
tolerance. Electronic control systems also can provide timer features
allowing some ovens to be programmed not only with start and stop times
but also to keep food warm once cooking is completed.

The disadvantage of these electronics, of course, is that one's gas oven
will not work in the event of an electric power outage. One can light
the cooktop burners with a match, but without electricity the control
system will keep the oven safely turned off -- and the family using
the backyard barbecue grille until electric service is restored.

Cheers,
The Old Bear

a catechism about how temperature is controlled in a gas oven. f I set the temperature to 350 degrees the gas will about-face on until the oven alcove 355 degrees...