Excess Air and CO

GA

I would add that if the CO is high when you have excess air in the range of 10% and above, it will be an indication of bad air mixing and bad combustion environment: If the velocity of the air flow is too high, it will entrain the combustion mix too fast out of the flame zone and thru the chimney. The flame shape and the optimum air volume/speed is important for a complete combustion and low CO in the exhaust gases.

I have more experience in Fuel Oil furnaces rather than Gas. Does it apply to the Gas fired furnace?

Yes. When firing a forced draft burner with any fuel gas and there is too much air going in through the burner or the air flow over the root of the flame is too fast the combustion process can be stopped before completion. The result is the presence of a group of chemicals in the exhaust gases called Aldehydes. The most well known one is Formaldehyde and this is known to irritate the mucus membranes (eyes & nose) making them run and itch. Mot flue gas analysers will show this as CO which is really un-burned hydrocarbons. So increasing the air supply too burners like this can make the problem worse. It does not apply as much to atmospheric injected burners as commonly fitted to catering equipment. These rely on the kinetic energy in the gas to induce some of the air required for complete combustion and are normally designed to produce a mixture in the burner containing about 60% of the total air required. The rest is introduced into the combustion chamber as secondary air.

Thanks for the reply Gasman.

Thanks for your reply. A hoof is a" Hands On Old Fart ". And i mean old. The oven in question was putting out 900 PPM CO, and I think that the manufactures know this, but say nothing. The manufactures have their burners tested by company's like Gas Consultants Inc. And from what I can see they have it down pat. They use very precise math. A good running oven should only about 7 PPM CO. ovens continue to put out massive amounts of CO. because the installation Manuel says only to crank down the hood orifice with a 1/2" wrench, and change the regulator. This converts the burners to sea level LP only, and ranges are not adjusted and tested when installed at altitude. The service Manuel's should be changed to reflect this.

It sounds like your installer/commissioning engineer is not up to the job. He should hve spotted the high CO and done something about it. That is after all what you paid him for.

who tests the oven in your kitchen with a combustion analyzer? if you find one, have them get in touch with me. and it is one thing to test and another to fix the problem. (too much CO from ovens is a big unnoticed problem) ALWAYS WELL VENTILATE YOUR KITCHEN.

We do not have a problem in the UK with height affecting the combustion of commercial kitchen equipment as the max elevation here is not great enough but I know it is a problem in the USA as this sort of question has been asked in previous postings.

As part of the UK system of proving competence anyone installing gas fired equipment needs a flue gas analyzer and the appropriate proof of competence before he is let loose on the public. Give the way professional competence is regarded in the USA I am surprised that a gas engineer over there is not required to test for CO when installing a range or oven at 8,000'. The ultimate solution is in the hands of the appliance designers and the test houses used. I was going to say that combustion engineering is not rocket science but it is. As a student gas engineer I had to study jet propulsion as well as gas burner design.

To reinforce you shout at the end:- in the UK a commercial kitchen is required to have an exhaust system and its associated fresh air inlet interlocked with the gas gas supply in such a way that the gas supply is interrupted unless the canopy fan is running correctly. The gas supply is only restored when all the gas taps have been proved to be closed by an automated gas tightness test using a pressure switch and a calibrated jet in a bypass around the main safety shut-off valve.