CO on a gas oven

Unknown

with a hypothetical problem I thought up. It could however be real. Here is the set up.

Service tech tests a natural gas oven while on a tune up on the oil boiler in an apartment complex. What a good tech to test that gas oven, maybe he is old #39. He finds that with the oven running there is 1100 PPM air free CO at the vent from the oven which is dumping into the kitchen. This range has coaxial spuds with a convertible regulator set at 6" W.C. gas pressure not adjustable. The oven works off a pilot with a safety valve in series with a oven heat control (thermostat).

What should he do? Is this repairable or is it new range time?

Here is the real tough part there is no range hood and no possible way to install one. This is an apartment complex so he being a good do bee he tests four other apartments all with the same range same conditions HIGH CO IN THE OVENS. The complex is on a master meter no individual meters for each apartment. A real dilema what should be done?

What are the possible causes?

What are the possible solutions?

J.C.A._3

Sounds like an \"improper mixture\" scenerio.

Most natural appliances are rated in the 3.5-4.5"WC range, and 6 is making the mixture gas rich.

I would be looking for a way to put regulators in each apartment. If there's a shut off for each unit, I think it could be done. (I have a sneaky suspicion that it's not the right answer, but it IS making me think!I think the pressure would drop too low if the boilers try to fire during a high demand situation, so the pressure was cranked up to make sure it doesn't happen, making the individual appliances overfire)

Now, a question for you, Timmie. What IS an acceptable reading for a stove, with all burners running? I did a conversion a few weeks back from natural to Propane, and found the oven to be around 45-55 PPM. Measuring the cooktop, about 6" above all burners firing, and draft hood running, I got between 26-30 PPM. Moving the probe out into the room, dropped the readings to 2PPM.

Of course, there is NO information in the conversion OR install manual reguarding the proper numbers. Just curious. Chris

Steamhead

Sure you aren't describing my stove?

That was exactly the level mine was. I solved it by opening the air shutter as far as it would go without causing the flame to lift off the burner. This shortened the length of the flame and kept it from impinging on the floor of the oven. I did check the input rate and it did not need adjustment.

Now the CO is less than 20 PPM air-free, and I have you to thank for helping me learn gas combustion.

In this apartment complex I would first do the same as I did on mine, then check the oven's input rate using differential clocking and adjust as needed.

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Steamhead

Chris, when you test the top burners

do you put a pan of cold water on them, or just test them as they are without a pan?

I prefer to use the pan, then I can test for CO under conditions of actual use.

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J.C.A._3

Frank,

There were no pots, pans or anything else to put on the stovetop. I think a pot of cold water would elevate the readings, but like you said, also give more "real" numbers.
As far as the oven burner conversion, it said to turn the screw in all the way, and open the air slot to the "propane position"....AKA all the way.
I guess that's why I asked the question of Timmie. Chris

Steamhead

I like to keep an old pan on the truck

for just this purpose. As with the oven, you're looking for impingement on the bottom of the pan. This will make CO go thru the roof.

The question of acceptable CO for a stove can be answered several ways. First, the ANSI/AGA standard specifies no more than 800 PPM. We all know that's ridiculously high!

You want to get the CO down as low as you possibly can. I would say you did well on that LP oven conversion. If the top burners hold those same readings when a pan is put on them you're probably OK.

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lchmb

ok..I'll try to

I would first check to make sure the spud is in the proper position for natural gas. I would than say with the slightly higher than normal pressure reading I would slowly open the air shutter and see if i could clean up the fire and co level. If that does not bring it to withing reason I would notify the gas supplier of the situation and check to see about inline regulator's at each stove. I would aslo notify each tenent that to be on the safe side get a co detector with display and keep a window open as much as possible till the situation could be resolved..
oh yea...as to cause, to much pressure not enough primary air...:) that's my guess..

Unknown

Chris 6\" W.C. is correct

pressure for this range. The regulator is not adjustable as it is either on LP (10" w.c.) or Nat gas (6" w.c.)

Allowable for an oven is 800 PPM that is way too high and needs to be lowered drastically. I like to see less than 25 PPM on an oven for cold start and then drop to less than 20 when at full run measured with thermostat set at mid point of around 325 degrees.

Measure top burners with no restriction and you should see about 10 PPM with a pan or skillet with some water in them sized to the grate area of the burner at high flame no more than 25 PPM.

Unknown

I will leave theis go a little longer to see if we can get some

others involved. See you tomorrow.

Mark Hunt

AHHHHH!!!!!!


The lovely co-axial spuds!

Did I tighten it enough or not?

Did I tighten it too much? Hmmmmmmmmmmm...........

The only thing the instructions say is to be careful about overtightening. No mention of testing though. So how would I know?

So what do I see when I look at the spuds?

Mark H

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Mark Hunt

Guys

If you put a pot of cold water on a top burner, you will get CO readings of 250+ppm. That is not a fair test. You could measure 4ppm on a top burner and then get 250ppm after a pot is placed on it. You impinge the flame every time you cook and the CO numbers go through the roof. Once the pot/pan heats up though, those numbers drop. It has nothing to do with proper adjutment of the stove, just a law of physics.

I use the "cold pan on the burner" to show people just how fast things can change. 4ppm to 250ppm in the blink of an eye.

If the homeowner let the sauce boil over on the burner, you will get higher CO numbers until it is burned off.



Mark H

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Douglas Hicks

And what is a co-axial spud? I am sure it is not a french fry.
I am in a lot of commercial kitchens and never worried about CO as the exhasut fan is always supposed to be in operation. Do I need to worry about CO?
Douglas Hicks
General Fire Equipment Co of Eastern Oregon, Inc

Weezbo

Tim...

I am not a natural gas service worker..so here is my take on service calls where the gas appliance is obviously not functioning correctly. i shut it off. get the occupants out of the place before going any further.then systematically go from my meter all the way along to make my determination...I get accurate information from the appliance center on the appliance...if it isnt functioning within thier parameters..i ask for any specific directions they have on the appliance.sans that...i will ask the homeowner what they have observed and restart the appliance after clearing the air as it were in the rooms or home...we have lots of propane appliances here and now we have natural gas. these two are not the same item at all.propane "Sinks"natural gas "Floats"however natural gas needs to be evacuated prior to restarting the devise of that i am positive.most appliances need a certain amount of cu' of air to burn properly if the problem stems from 65K appliance in a 6X10 room....then it most likely never worked correctly.anything that is obviously problematic are what i will help someone with .in most instances i dont go looking for problems as that isnt my particular line of endeavour.to me it sounds like incomplete combustion with insufficent air.

curiousity kills

co in oven

Ovens could need cleaning???

Steamhead

I've found

that if you set the max flame height to just below the pan, it won't impinge so much and the CO will usually drop below 75 PPM. If the flame is too high the CO will stay over 200 PPM. To me, that's a big difference. And the flame height you get this way is usually pretty close to the rated input. From there, I fine-tune to get CO as low as I can.

I had one lady with a very old Oriole stove where you could smell the aldehydes about 5 seconds after she turned it on. I got 950 PPM and rising! No regulator or rating plate either. These burners fired straight up toward the pan instead of to the side as most newer ones do. I screwed the spuds down a bit to get the maximum flame height down to just below the pan. This cleaned the flames up nicely.

The best part on this one was, she said she was getting more heat from her burners than before. This was because the hottest part of the flame was now just below the pan, and was not being quenched. This illustrates how CO is wasted fuel, besides being toxic.

I think any test that reflects the way an appliance is actually used in the field is a fair test. AGA allows manufacturers to test with the oven floor removed and no pans on top. I think that's dead wrong- who uses a stove with no oven floor? Who cooks without pots and pans?

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Unknown

Douglas a coaxial spud

is used only on residential gas equipment and in particular only on gas ranges. Commercial equipment should not have coaxial spuds. What are they? The brass piece that the burners slip onto which has a hole (orifice) in it is called a spud. A coaxial spud is one which allows the equipment to be easily adjusted for either LP or Natural gas with out changing the spuds or redrilling them. The rule is to turn the spud with a wrench all the way down down for LP and all the way out for Natural gas.

I edited this an added that waist high infrared broilers do not use coaxial spuds. The ranges do come however with a spare LP spud under a little plate up in the top burner area for conversion. Infrared burners have very low CO with very good burning speed.

Steamhead

It's also called a hooded orifice

The most common version consists of an inner metal cone, and an outer cylindrical hood with a hole in the end that screws down over the cone. The clearance between the cone and the hole determines the orifice size.

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Unknown

Mark there is a way

to adjust the coaxial spuds and also a way to reduce CO emissions with top burners running with cold water in a kettle. The flame impingement issue is something that customers need to be instructed on. Years ago gas utilities that sold white goods, ranges and dryers had what was called a "girl in white". Her job was to go to a customers home who had purchased gas equipment and instruct them on the proper use of equipment.

I had to spend a week with her as part of my training when I first started out. She knew things about combustion on gas ranges that no one I have ever met since knew. The proper way to turn on a top burner is to first turn it on low (they usually have three click positions) if not you can throttle it down to about 1/8" of flame. After five minutes place the kettle or skillet on the burner let it run for five more minutes and gradually turn it up. If you do this the impingement factor is much diminished and CO levels will stay very low. I am sure Jim Davis must cover all this in his class so I am probably teaching something you already know. There are many ways to keep CO emissions low on gas cooking equipment if the equipment is used properly and kept clean. Cleanliness on gas cooking equipment is a big factor by the way. Proper sized cooking utensils are also a must no kettle or skillet should extend more than one inch all the way around beyond the grate area of a burner.

What has happened with gas cooking is it has now gone to the appliance stores to be the marketing outlet. They know diddly about cooking.

The gas company did away with the girl in white when they stopped selling white goods. I am thankful for all the little adjustments she taught me over the years. She also taught me how to cook, not that I am any good at it, I am the outdoor grill chef.

Thge new sealed burners used on a lot of equipment are a different story by the way. The manufacturers of those state they have low CO emissions due to design. I have not however found that to be so.

Something to think about on the holidays when 4 (four) top burners are going and an oven and no exhaust, no wonder everyone has a HEADACHE OR WORSE.

Mark Hunt

Good points Steamhead


Have you ever had anyone complain about things taking longer to cook?

Same thing applies to the oven. The manufacturers want max heat output as do the consumers, but quite often that accounts for huge CO production. I have had customers say that they have had to increase baking time, though not enough to cause a huge inconvenience. Ovens are a major pain to adjust. I installed a wall oven for some folks last year, and the only way to adjust anything on it was to take the thing apart! I had to be a contortionist to get at the co-axial spud. The best part of this was the notice inside the packaging warning customers not to keep birds near the cooking apparatus as "fumes" could be fatal!


Excellent post Steamhead!



Mark H

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Unknown

Eric, you are right many times a dirty oven can

be a problem.

Unknown

Steamhead mentioned the odor

of aldehydes. Many times a top burner or oven pilot which is adjusted too high will cause impingement adding to the already high levels of CO from cooking. If you have aldehyde you have CO, but you can have CO and not smell aldehydes.

Unknown

I am of to church

I will check back this evening to see how we are doing to solve this problem. Good info so far keep it up as this is how we learn. Do not just rant, educate that is what this site is all about.

Mark Hunt

\"Sleepy on Thanksgiving\"


When I was working for a larger company, I challenged the service techs to bring their clip-on CO monitors with them to Thanksgiving dinner. Of the 5 techs, 2 reported ambient CO levels in the house at 12 to 15ppm. The others had no readings, but their were no gas cooking appliances in those homes.

Around here, 10ppm will get the home evacuated by the utility. Imagine if they did that on Thanksgiving and Christmas! I can just see a bunch of firemen carrying out the turkey saying, "Here's the culprit!"!

Gas cooking appliances are not made with servicing in mind, as you know very well. When I run into them I have a little mantra I repeat, "pleaseletitbeok,pleaseletitbeok".
I do not enjoy taking the things apart, not to mention the looks you get from the customer when their stove is in pieces on the kitchen floor!

Have you ever tested an electric oven when it goes into "self-cleaning" mode?

Mark H

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Steamhead

A bit more on aldehyde odor

This is a sweet/sharp/stuffy smell that vaguely resembles the smell added to unburned natural gas so you can smell a leak.

Tim is dead-on (no pun intended), as usual- if the smell appears when the burner is turned on, you definitely have a CO problem, but the lack of the odor doesn't mean you don't have high CO.

If you go into a customer's house and smell aldehydes, BY ALL MEANS get the customer to OK a CO test on the stove. If they say someone told them the odor was normal, tell them the test will let them know for sure. You just might save their lives.

What's that you say? You don't have a CO tester? Then you really, seriously need one! How can you be sure without testing?

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Steamhead

Another thing about ovens

On most residential units, air is admitted to the oven burner area thru slots or vents to the outside of the stove. The total amount of air available to the oven burner is limited by the free area of these vents.

Opening the air shutter on the oven burner thus has the effect of routing more of the limited incoming air to mix with the gas before it is burned. More primary air, less secondary air. It shouldn't affect cooking that much, but as Mark says there are exceptions. If you have to reduce the input rate to clean up the flame, that might cause longer cooking times.

Also make sure those vents are not blocked with dust, cobwebs, etc!

P.S. The Dead Men used to use canaries deep inside mines as an indicator of oxygen depletion. If the canary passed out, you evacuated the mine right away!


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Unknown

This problem is repairable

and no it is not new range time until we have checked and done these steps.

The tech should:

1. Remove the burner from the oven and clean the burner.

2. After removing the oven bottom observe the burn pattern on the spreader. Note if any carbon deposits (in our problem there is a little carbon). The burn pattern should reach to within 1/2" of the edge. If further then it is probably over gassed. If less than 1/2 " it is undergassed which in some cases can cause CO.

3. Clean the oven bottom.

4. Check secondary air openings in range bottom to insure they are not blocked. These openings can be tricky and sometimes the range is not designed to be built in but free standing which allows air on all four sides to enter. Also watch out for mop boards placed over secondary air openings on the front bottom of the equipment.

5. While the burner is out clean the oven pilot orifice.

6. Replace the burner leave the oven bottom out or work through the broiler drawer if it is the type with a Lo-broil. It is easier to work with no oven bottom.

7. With the oven bottom removed bring the burner on and observe the flame, it should be a blue sharp flame with three distinct cone patterns.

8. Adjust the coaxial spud for a good flame pattern. Sometimes opening it up just a little more can change the inspiration of the flame.

9. Open the air shutter on the burner to full open. If the flame sharpens up and starts to lift off the burner that is okay. It will usually settle down when the oven bottom is put back in place.

10. Shut the oven off and replace the oven bottom. Close the oven door insure it is tight. A loose oven door or bad gaskets can cause streaming. Streaming is combustion products escaping out the door and contaminating the air for combustion for top burners.

11. Bring the oven back on and if possible observe the flame, lo broil models will allow this waist high will not.

12. Now retest the flue gases coming out of the oven. You want to see less than 25 PPM. It is possible to get the oven down to as low as 5 PPM believe it or not. You can if readings are high try lowering the spud toward the LP position and at the same time watch the CO. Many times this will clean up the flame and lower CO.

13. With an oven thermometer test the oven temperature with the oven heat control set at 325 degrees. It should take the oven about 15 minutes to come to full temp and cycle off. This will help you see if you are close to correct input.

14. If possible and you have a gas meter then clock the meter on the 1/2 foot dial. It may take a long time to make a rotation so you might want to bring on another appliance and clock them together. Then shut off the oven and clock again,the difference is what your oven is burning.

So what is the answer to our hypothetical problem. Very simple all of the ranges are designed to be free standing. That means they can not be built in to the cabinet area. These are closed in on both side which is restricting secondary air. We would have to leave them off and red tag. A modification to kitchen has to be made or new ranges with built in features purchased.

Mitch_4

Remove

remove the tinfoil that the nice old lady has put on the bottom of the oven to help keep it clean. You can cut Co in 1/2 by doing that. Clean butrner and orifice. set flame so it does NOT impinge on flame spreader. (back off the co-axial about 1/2 turn. Clean the bottom are (broil pan so that airways are not obstructed.

CO happens when running rich on fuel,lean on O2, impinging on cold surfaces.

Mike

Jim Davis_3

My 2 cents

One thing I found about ovens is that the factory reps know less about them than we do. Also found that most installation manuals provide bad information. Had a court case once in Oklahoma where the mother and two children had been poisoned by their gas oven. Children had learning disabilities and partial loss of hearing. The oven had been purchased to be used on natural gas, but had been set up for LP. Coaxial burners and two step gas valve. When testing the oven set up for LP(using natural gas), it produced over 1000ppm after it was warmed up.(even higher getting there). Then I had an appliance service tech adjust it correctly, according to factory specs for natural gas. After this was done the oven produced over 2000ppm. Thank goodness it had been adjusted wrong. No oven can be adjusted correctly without a CO analyzer. Low gas pressure can be as problematic as high gas pressure. As far as top burners, trying to adjust them with a pan on them can be misleading. This one I have to depend on people that specialized in oven testing(Bruce Davis with AEG)& repairs but their findings were interesting. If you adjust an oven with an aluminum pan on it, each diameter on pan creates different readings. Changing from aluminum to cast iron to steel, all give different results. I agree with Timmie that the proper way to use the top burners is start low until the pan is heated. Now if we put 100 women in a room and ask them this I would guess 99-100 wouldn't have a clue. Testing and adjusting to the lowest CO reading no matter what technique we use is the best plan of attack.

Kal Row

at least GE is thinking right...

my new profile range JGS968BHBB - has very tall grates, provides good air supply and reduces impingment - but my wife says, the grates are too heavy to lift for day-to-day cleaning

Steamhead

Jim, when they tested with the different pans

on the top burners, was the flame impinging on the pans or not? I can see impingement on different pan material causing the phenomenon you describe.

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Unknown

It is a good idea

to go to a cooking class that teaches about the use of different materials used for cooking such as glass or pyrex, cast iron (your faithful old skillet), aluminum, steel, copper etc. They all work differently and distribute heat differently which in turn affects combustion both at top burners and in the oven.

In the oven rack position, pan location and as mentioned above material of the cooking utensils.

The worst thing ever invented is the aluminum foil spill over stuff or as someone mentioned the lady who lines her oven with the stuff to keep it clean.

Mark Hunt mentioned CO with an electric range on self cleaning. You should see the CO with a gas self clean oven. Gas at one point to get high temps to clean the oven run both oven burner and waist high broil burner. A very good idea to have the kitchen well ventilated. My Caloric self clean is actually done with all of us out of the house including the dog. The last time I used the self clean I checked my CO Experts CO monitor when I came back in and it was at 7 PPM the tester is about 25 feet from the gas range. I might mention that my oven runs at less than 25 PPM air free and my broiler around 30 to 35 PPM. We do not use the broiler however as we cook a lot with our outdoor grill year round. Just shovel the snow away and have a steak.

I would love to have Jim Davis talk about "Pellet Stoves" sometime. I used a pellet stove to heat about 3/4 of my house. (gas is too expensive) I have it set up with very low CO at the flue exit point (sidewall vented)it is around 150 to 200 PPM depending on what kind of pellets I burn. Is that good Jim?
I take it completely apart every year and clean it and reassemble and reseal the flue. I am actually very wary of that thing and am testing it all the time.

Just think of all the stuff in our homes that if not cared for properly and tested and used correctly can KILL us!!!

Mad Dog

Thanks for posing the question Timmie

C'mon Steamhead....you already "own" the steam now you wanna be a CO expert too!!!!~!! More power to ya, Pal. Mad Dog

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Steamhead

I'll never be \"the CO expert\"

as long as Tim, Jim, Mark etc. are with us. They're the best IMHO.

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