My experience and observations are that the lower element does most of the
work in both gas and electric. The upper element in an electric oven is for
broiling and, maybe, preheating. In the gas ovens we have, the lower burner
does the work, while the upper burner is for broiling.

The thermostat controls the gas valve by shutting it off and turning it
on -- shutting off the flow of gas, thereby turning the oven off, and
restoring the flow of gas, thereby allowing the oven to turn on. Both types
of ovens operate in on or off mode, there is no such thing as an oven that's
"on low." When an oven is on low, it is set for a low average temperature.

I'm not aware of any recipes that require upper or lower heating, except for
broiling.

I know nothing about industrial gas ovens. I've used and managed very large
electric annealing ovens, but those were used in temperature ranges of 1300F
and annealed brass and copper by the ton.

As for the moisture generated by the gas oven as opposed to the "dry" heat
of an electric oven, I wouldn't worry about it. You'll probably find that
the moisture released by the baking process itself overwhelms the bit of
moisture generated by burning gas, and that the gas-generated moisture
dissipates rapidly. This will undoubtedly start a thread/flame from those
who will claim that the amount of moisture is significant, since I remember
a thread recently that pounded this topic to death, but it's not worth
thinking about.

As for a web site or book, I haven't looked for any. You might try a google
search on oven gas control and see what pops up. You could also check out a
boiler manufacturer, ours is Slant Fin, and see what they have in the way of
discussion. The principles of an oven and a gas-fired boiler are identical.

Not to belabor a point, which I am, but we have 4 boilers in series with a
computer control that fires them in sequence. The control process works by
measuring the ambient (outside) temperature. It the ambient is above 60F,
nothing happens. If the ambient is below 60F, then the controller measures
the ambient and the discharge water from the boiler. It checks the
temperature set on the control panel and the control band. There is another
control, one that moves the set temperature up and down by a ratio, but
let's not get too confused here.

Consider an ambient of 25F (today's temp), a base water temperature of 110F
and a band of 3F. These are my conditions today.

The control program is set to raise the temperature of the water to the base
water temperature plus 70F minus the ambient. Today, this works out to 110
+70 - 25 => 155F. The control band is the tolerance within which the
discharge water must be maintained. I have a temperature gauge on the
discharge pipe and a temperature gauge on each boiler on the discharge side.
I know that in this temperature range, one boiler will be sufficient to
raise the total water flow by about 10F, which is about the temperature drop
between output and input; one boiler will, therefore, just about maintain
the desired temperature under these conditions.

So, when the water temperature falls to 155 minus half the band, or 155
minus 1.5 degrees or 153.5, the boilers start to come on or fire. They will
go on, one at a time, and continue to come of in sequence and to fire until
the water temperature hits 155 plus 1.5, or 156.5F. Then they will start to
shut off, the first to fire will shut off first. There is a 2 minute lag
built into the firing and shutting off process to allow the system time to
stabilize.

A kitchen oven works the same way, except that it has only one heating
element. There is a desired temperature, a control band, and a mechanism
for turning the heat on and off.

Barry

"Alan" > wrote in message
...
> how does the thermostat control the gas valve when tempreture overshot?
> the reason i asked for the upper gas burner(element)is bcos some baking
need
> upper tempreture more than lower temppreture,in electric oven you can have
> seperated upper or lower element,but in gas oven case,how can we get it?
> I was told that industrial/commercial gas oven does have upper and lower
> burner element,is that right?cos i haven't seen one like that before.
> i feel that gas oven tends to generate more moisture(gas?)than electric
> type(tends to be dry type)and resulting of different
> quality for the baked product.
> is the any book or web site i can learn more about gas oven?
> thanks
>
> "barry" > wrote in message
> t...
> >
> > "Alan" > wrote in message
> > ...
> > > Thanks for your advise:
> > > my gas oven heat up to the tempreture according to the preset heat,but
> > > sometimes when it overshot,the gas burner still fire
> > > and never went down,i wonder is the thermostat still in proper
function?
> > > where can find the thermostat from the oven,where can i get
replacement
> > > parts if it is not working.
> >
> > The thermostat is an electric device. You can probably buy one and
> install
> > it yourself, if you have the manual or can get it online and you can
find
> > the part. If you can't do this, you'll have to buy the part and have it
> > installed for you. I have done this on electric ovens, when it's just a
> > matter of replacing a burned-out element or thermostat. On the other
> hand,
> > electricity isn't explosive and electric equipment isn't as stringently
> > covered by various Building Codes as is gas equipment. ("I smell gas."
is
> > the surest way to get a bunch of people off their duffs and into your
> house
> > pronto. when was the last time anyone said "I smell electricity?")
> >
> > The part will probably cost about $30 and the service call will be
around
> > $100, both plus tax. Total cost around $150, just as a guess. As an
> > example, I remember the heating element on a Thermador electric oven
cost
> > around $50 and took about a half-hour to replace.
> >
> > I have 38 gas stoves with ovens and 4 325,000BTU boilers. I do not do
> any
> > of my own gas-unit repairs, even though I am a very good mechanic, at
> least
> > on automobiles and other machinery. By the nature of your questions, I
> > assume you are not a qualified mechanic or contractor.
> >
> > I also do not repair gas ovens. I replace the stove when the oven
fails.
> I
> > figure that fixing an oven is just wasting money. A gas oven has a
> service
> > life of 10-20 years, depending on use and quality, so if it fails after
12
> > years, that's it. We buy good quality, reliable stoves and spend
anywhere
> > from $325 to $500. (30", 4 burners, standard oven with broiler, pilot
> light
> > or electronic ignition).
> >
> > As for modifying an oven to add a broiler, forget it. There are so many
> > possible Building or Municipal Code violations here that I can't even
> begin
> > to list them. If you buy a new gas stove/oven, make sure that your
> > installation meets your local Code.
> >
> > Barry
> >
> >
> > > there is no upper burner(upper fire)for this gas oven,can i make one
for
> > > myself?how to do it and where can i get parts?
> > > any web site can teach to diy a gas oven?
> > > thanks
> >
> >
> >
>
>