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We get a lot of questions about using gas to fire our bread ovens but we worry about the safety of gas in an oven. Could a faulty valve leak gas into the oven or could the customer turn too much gas on too soon so that when the oven was lighted it would blow up? We decided to ask some experts we knew. The best answers, I think, were provided by John Fisher, a masonry heater and oven builder. who advises, "Light the nozzle before you stick it in the oven." and from Alex Chernov, who recommends the use of gun-type burners which are located outside of the oven chamber and hence avoid problems with safety controls.
Here is the string of our conversations:
Date: May 1, 2007
John,
Thank you.
"Light the nozzle before you stick it in the oven." That sounds very logical, simple, practical and safe. We were well on our way to a ready-fire-aim solution but I think you got it right.
Best,
As far as i know the gas nozzle gets lit before you
stick it into the hole. if it is managed that way,
there should never be gas building up in the dome.
As a safety device the gas slot works in very low
volume inputs and is automatically mooted when the
volume of gases comes up to normal combustion level.
so i can't imagine how it work well as a pressure
release in an explosion, or even prevent explosion by
leaking gas fast enough as it is being pumped in.
The safety is in keeping the unburned gas out of
the oven....i would think.
respectfully,
_____________
And from Alex Chernov
Hello everyone.
I would support John's opinion that a slot will not work. If it is large enough (and it would have to be really large to draw out gas at the same rate as it is delivered) it won't be an oven anymore as most of the heat will escape through the slot.
I agree that your aim should be to keep unburned gas out of the oven.
Another area you have to pay attention to is the burner construction. Most gas burners are designed to work in the environment where water or air constantly draw heat away from the burner. Such burners are not designed to withstand high temperature levels at the head and have safety devices that shut them off as temperature of the burner's head rises significantly above a preset limit. Such burners cannot be used in the high temperature environment of a closed dry air chamber.
Gun-type burners permit location of the burner outside of the chamber and hence avoid problems with safety controls.*
Alex
Hi Jim:
I'm not sure. I've never heard of a gas slot in an oven. Seems like it would add complication, since it would need to be routed into the chimney. I'll copy this to Alex Chernov and John Fisher, who are also well versed in these matters and may have an opinion.
Best ..... Norbert
Jerry and Norbert,
From time to time we get inquiries about using gas to fire our clay ovens. See below. Figuring out how to rig a gas burner in the oven is the easy part but I want to be sure gas won't build up in the dome of the oven and blow the dome through the roof when the customer tries to light the burner.
I understand that masonry heaters, especially the ones vented at the bottom, have a gas slot in the top to vent gasses out of the heater into the flue. Do you think we should put a gas slot in the top of the dome of our oven vented into the flue or is it too small of a space to worry about?
Best,
Jim,
I get a lot of questions about using gas in bread ovens. I know this takes away from the whole "wood fired oven" idea, but any information you could provide would be greatly appreciated.
Also, could you please call and speak with John* about this issue. He is a mason looking to install a bread oven. He's a pretty nice guy and I was unable to provide him with enough info on this subject.
Thank you,
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