Setting up the air to fuel ratio High for Low Fire Your thoughts

RayWohlfarth

I was taught the best way to set the air to fuel ratio for a burner is to start at low fire. This did two two things. It allowed the burner to run longer so the loop doesnt heat as quickly. Secondly, its theorized the boiler spends most of the time at low fire. Im starting to see some people suggesting that you start at high fire. Just curious about your procedures.

Thanks

HydronicMike

Each manufacturer usually determines how they want it. With oil, usually I have seen and set up in high fire which will usually be your best combustion/efficiency, then low fire seems to be what it is, as long as it's safe.

EBEBRATT-Ed

Depends on the burner.

I assume we are talking power burners. My thoughts:

Most oil burners do better on high fire than low fire. More air through the blast tube at higher velocity =better mixing.

Gas the same thing but probably less disparity.

Most "American Burners" are set up low fire first then high fire.

On most high fire is better and low fire you sort of live with what you get as @HydronicMike mentioned

However I did a bunch of Riello gas burners in my last years of working from 1,000,000-6,000,000 btus and Riello stressed that (and the burners are designed) that you have to set up high fire first which was something I struggled with after doing the opposite for 40 years.

RayWohlfarth

Thank you all. I appreciate it

retiredguy

We serviced almost any burner ever made from Junk to Cadillac, although most of our work was with Power Flame Burners C's and B's up to about 30,000,000 btu's. First, I would light the burner on low fire, rough set the low fire, and slowly increase the input to maximum required for that boiler. Then, I would adjust the high fire first for best firing and slowly return to low fire checking the firing using the analyser I had at that time. Early on we used the Hay's Orsat (junk), the Bacharach Dumb Bells, (antiques) , and lastly some kind of electronic analyser. Again, I retired in 2007 soI be a little behind time.

ScottSecor

I agree with the comments above. Keep in mind that the majority of the burners and boilers we worked on were grossly oversized. In almost every case, we were not the installers. Instead we were the start-up techs or the service tech.

With commercial oil burners we regularly dialed in the flame on high fire first, this was especially true with Carlin oil burners with multiple nozzles (two or three). In many cases (with oversized boilers and burners) we would dial them in on low fire, and lockout high fire completely.

With Powerflame oil or dual fuel burners, they often had BPS (bypass) nozzles. These burners did not suffer as much as the Carlin CRD burners did on low fire. If we knew the system well, we would dial them in at the ideal firing rate and set the controls to "search" for this range. Most of the time it was approximately seventy-five percent of the maximum firing rate.

On "modern" (late 1970's through late 1990's) Industrial Combustion oil (or dual fuel burners) we would follow the same logic as above.

On "old" (1950's through early 1970's) IC heavy oil burners they used an air pump to inject air to assist with combustion, much more forgiving than some of the modern oil burners. I will skip the oil cup heavy oil burners for this conversation.

With regard to gas power burners, in almost every case the best numbers came from high fire or near high fire. It was always a challenge, ideally the burner would modulate to low fire once above the flue gas condensation range (typically 140 degrees). The problem was, the efficiency would drop off significantly on low fire. We often see Powerflame, IC and occasionally Midco around here in NJ.

Finally, in the late 1990's we installed two Powerflame burners with the new Honeywell "Control Links" digital air and gas controls. For the first time in my career we were able to dial in the air independently from the fuel. The controls were a nightmare. I spent the better part of one winter in the boiler room on the phone with Powerflame, Honeywell and a few other suppliers of electronic parts. Oddly, the buildings that housed these steam boilers were demolished about a year after we installed the boilers and burners. Maybe this was a blessing?

EBEBRATT-Ed

@ScottSecor

Aw come on!!! You can't skip the old rotary burners especially on #6 oil. I never went home clean, I was always filthy. Mostly #4 oil though.

The company I worked for sold Petro rotary's starting in 1920s and they weren't the best. Johnson, Preferred Utilities and York had some good rotary's. Around here it was a lot of Petro, Todd, Ray, and Preferred. Last I knew Preferred still made rotary's.

ScottSecor

The rotary oil burners were so simple I struggled to comprehend how they worked. It has been almost forty years since I worked on a rotary cup burner, but here is what I think I remember.

Store oil as thick as Vaseline in a ten thousand gallon tank underground. On high end systems, heat the tank with a steam heat exchanger inside the tank. On the more popular systems, they heated and pumped this thick oil with a high voltage (208 or 440)three phase heaters. Then they drooled the oil into a metal (steel?) open end cup and allow it to sling off the edges of the cup. If memory serves they were ignited by a three foot long gas pilot. The faster the cup spun the more oil would be slung into the fire. The faster the cup spun, the faster the fan would spin, increasing the air flow as you increased the oil flow. Let the cup get dirty, everything would get covered in sludge and or soot.

I agree with the mess, dirt/oil/soot embedded on my face, hands, skin, clothes, tools, etc. There were many times my wife would have me undress in the kitchen and toss the clothes in the garbage can (outside). The good news is the racoons would not go near the garbage when the oily clothes we in the can.

HVACNUT

Manuals I see usually prompt a service mode to start in high fire. Throttle screw adjustments as necessary. Then low fire. If low fire needs to be adjusted, its a separate low fire adjustment screw, not the Throttle screw. If high fire is good, you typically don't need to adjust low fire. A WM rep told me once if you do low fire first, it will throw off high fire readings. I just do what I'm told.

captainco

Back in the 80's and 90's there were energy crunches, government programs paying for fuel saving investments. I worked as a combustion assistant and doing all their combustion testing and upgrade recommendation. These guys were amazing in calculating fuel usage and degree days. They factored in sunshine, clouds,rain,snow and wind. They got paid 40% of their customers sav ings for 7 years. Wow!

What this meant is after making adjustments to their boilers (commercial) they would audit their fuel bills and usage. In all cases, any burner that had run in low fire and switched to high fire only, saw a minimum of 20% reduction.

Going back to the question here, it doesn't matter which one you adjust first but how you adjust them. Low fire is to create smoother light-offs and fewer flame failures. High fire, which is the only efficient mode of a burner is set the best it can be set without messing up low fire. Each needs to be be checked back and forth with each adjustment.

Any burner that is larger than 3,000,000 should have a low fire start and a low fire off. Larger burer should have a low fire start, modulate to high fire and then modulate to off.

How many manufacturers of burners have spent years of real experience in the field. You are all smarter than them and still listen to their best guesses. Last year on the internet I listened to an engineer from a large boiler burner manufacturer do a combustion training. 40 year's experience?? The guy had no clue to what he was talking about.

IF you know something from personal experience trust your self. If it is only hearsay, we are accomplishing nothing.

EBEBRATT-Ed

@Scott Secor at least you got in the kitchen. I had to change in the garage. I can't remember the last time I worked on one or ripped out my last one. They were still running in 1980 but by the 90s I think they were pretty much gone gone, but I wasn't doing much burner work then. When I started in the early 70s everything was mostly #4 oil as far as schools etc. Even small elementary schools were #4 with a 20 gph burner. That gradually changed and the early-mid 80s was just crazy with oil to gas or gas oil conversions.

RayWohlfarth

Thank you all I appreciate it and I remember the rotary cup burner. My mentor warned me how dangerous they were.

ratio

https://forum.heatinghelp.com/discussion/comment/1873485#Comment_1873485

How so, Ray?

RayWohlfarth

Ratio not sure but my mentor said they were dangerous Said they leaked a lot I never saw it but we only worked on one

retiredguy

I serviced and repaired quite a few Johnson rotary burners firing both oil and gas and never had a problem with them. Were they dangerous, no more than most any other burner, as long as you knew how to work on them. Were they crude, yes, but they would burn almost any fuel oil you could pump through a pipe.

EBEBRATT-Ed

The oldest rotary I saw was my first year fresh out of school was a really old Ray burner burning #6 oil in Holyoke, MA. I drive buy the building sometimes and still think about it.

So, I got sent they're by myself to clean the boiler. Big old HRT boiler probably 15 feet long. So, I spent all day sucking soot and punching tubes. No one told me to start the burner but

When I got done, I wanted to see the burner run because "hey I am an oil tech now". Now fresh out of school back in 73 we had worked on "normal" burner controls Fireye 6058s, 6070s etc and the newer 5022s and some of the Honeywells. All had prepurge, pilot trial for ignition, main flame and postpurge …..standard stuff.

This old one had a "Ray" control which I had never seen. I looked at some switches that were off and flipped them on.

Surprised the hell out of me the burner motor started, the gas pilot lit, and the oil valve opened all at the same time and it took off and ran!!!!!

Scared the crap out of me. Had a gas pilot but not proven, no prepurge, no post purge. The only flame detector was an old Honeywell "pyrostat" that sensed heat from the flame.

Basically, as safe (or unsafe) as a stack switch with a 90 second flame failure timing on a 60gph burner on #6 oil.. Unreal. This thing must have been installed in the 30s or earlier.

RayWohlfarth

@retiredguy LOl so I fell for the whole Tell the New Guy Its Dangerous Ploy

@EBEBRATT-Ed We are fearless when young There was lots of crazy tuff in boiler rooms back then