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Checking an oil fired burner inside a converted Rayburn

JamesI
JamesI Member Posts: 8

Hi,

I service my converted Rayburn Royale (1969) myself, have done for years, but one issue has always puzzled me about the advice and I wanted to get some other opinions on it.

Standard way of checking the air/fuel mix is right (draw, fuel rate etc) is to check for a blue flame (as opposed to yellow).

The trouble is that in a converted Rayburn, I have to open the door to check. But as soon as I open the door, I completely change the air flow so anything I observe is useless. I remember from school when we played with Bunsen Burners, when you change the air intake the flame changes immediately, not after a few minutes, so it's not like I can 'catch' the way the flame is without the door open if I'm really quick.

So does anyone have any clever way round the problem?

Comments

  • pedmec
    pedmec Member Posts: 1,066

    That is why you use a combustion analyzer.

  • JamesI
    JamesI Member Posts: 8

    But where?

    I don't have a combustion analyser, but if I did, where would I put it?

    Open the door and stick it in? Same problem

    In through the flue box? Same problem

    Basically, the system is sealed up from inlet vent to flue cowl, and it's quite deliberately designed that way.

    Flue dampers, as I understand them, work by letting a small amount of air in from the room to the flue system and that small amount of air affects the draw (if it didn't the flue damper wouldn't work). So anywhere I make a hole in the system, whether that's to look in or to stick a probe in, it's going to act like a flue damper and change the draw.

    I'm not going to be testing the system I actually want tested, but rather it's testing a different system with that hole in it. Doesn't matter if it's a door, or a flue access plate, or a flue box cover… Anywhere I open a gap to get at the flue gasses is going to change the very system I'm trying to check is OK.

    I could climb up on the roof and analyse the gasses coming out of the flue I suppose…

  • Steamhead
    Steamhead Member Posts: 17,380

    Drill a suitable hole in the smoke pipe between the Rayburn and the draft regulator. The analyzer probe goes in the hole when you test. Simple.

    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
    SuperTechGGross
  • pedmec
    pedmec Member Posts: 1,066

    steamhead has just explained it

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 9,378

    Are you planning on purchasing a combustion analyzer just to do one piece of heating equipment, once a year?  You know that once you purchase that analyser, it needs to be calibrated each year.  Somehow I don't see the logic.  There are companies that have those analyzers on the service truck. And even if you pay dearly for a service call in your area, it will take years of overpriced service calls to make up the difference in the cost of a combustion analyzer and the annual calibration that goes with it.


    Just a thought: look for a company that already owns one, and pay the service tech for a burner adjustment and combustion test.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • JamesI
    JamesI Member Posts: 8
    edited April 26

    You both seem to have misinterpreted my question, my fault for not being clear enough, I'm sure. The key part of my question was "one issue has always puzzled me…". I'm not asking for a solution, I'm asking for an explanation.

    There currently is no such hole, nor is there any such hole in any of my friend's oil ranges. So although I can see exactly how drilling such a hole would be a solution, it doesn't explain why there isn't already such a hole in every oil fired Rayburn in the country as standard… if such a feature is necessary.

    Basically, I'm asking how it is that such solutions are not common and yet seem the only answer, or perhaps I'm asking why such modification has become necessary, why there isn't a much simpler system already. I doesn't seem to make sense.

    For background - I had a (fully qualified) heating engineer fit a new woodburner last year. As part of the fitting he installed a CO detector, a legal requirement for the fitting to be signed off, even though we already had three in the house. He said "if you get any warning from that, call me, otherwise, it's all good". And that's exactly what I expect. If there's something potentially dangerous about a system, I have an alarm to tell me something's wrong, otherwise I can relax in the knowledge that it's working.

    I was puzzled by the conflicting information regarding oil-fired heating which seemed to imply that some special methods were required to obtain that same state of relaxed assurance (I obviously have a CO detector in the same room as the Rayburn too), and yet were far from standard and not even a legal requirement. Why is it that the necessary safety protection for my woodburner is a legal requirement, but I'm having to find out from some helpful folk on an internet forum what the necessary safety protection for my Rayburn is?

    (Further background, I've obviously had a few engineers service the Rayburn when I first moved in, I didn't just guess how it was done, I watched them and copied. None tested the flue gasses, none drilled any holes. They just took the burner out, scraped to carbon off, replaced the wicks, vacuumed the chamber, re-lit it and then left

    I live in a very rural area. There are two oil-fired heating specialists within 50 miles of me, I've had them both out and both repeated the above, the last one even told me to leave the bottom door slightly ajar all the time which another helpful internet expert told me was positively dangerous advice.

    Long and short of it is that I'm out of engineers, so not really a solution for me)

    Anyway, it looks like I'm going to remain baffled. Thanks for trying though.

  • SuperTech
    SuperTech Member Posts: 2,430

    You don't need to hire an engineer, just a good oil burner or HVAC service technician. The reasons why nobody has done the combustion analysis should be obvious. Laziness, incompetence and negligence. Back when the boiler was installed it was common practice to look at the flame and call it good. Few boiler manufacturers have any combustion testing ports, the boiler doesn't come with the flue pipe attached, the installer provides that and should drill the hole for testing.

    GGrossMikeAmann
  • Steamhead
    Steamhead Member Posts: 17,380
    edited April 26

    @JamesI wrote:

    "You seem to have misinterpreted my question, my fault for not being
    clear enough I'm sure. The key part was "one issue has always puzzled
    me…" I was asking for an explanation, rather than just a solution."

    That was uncalled for. We didn't misinterpret your question at all. That is the correct method. And this is the explanation:

    The results of this "laziness, incompetence and negligence" can be breathtaking:

    Here are a couple more that don't display properly. Copy the links and paste them into your browser to view:

    https://forum.heatinghelp.com/discussion/132567/one-of-the-worst-maintained-oil-fired-boilers-weve-seen

    https://forum.heatinghelp.com/discussion/146509/quot-serviced-every-year-quot-we-were-speechless

    I've long maintained that in many cases, fuel suppliers doing boiler or furnace service is a conflict of interest. What motivation do they have to make your system run efficiently, if it means they make less money on fuel?

    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
    SuperTechGGross
  • JamesI
    JamesI Member Posts: 8

    "That was uncalled for…"

    I didn't mean to offend anyone, but to be fair the 'explanation' came after I wrote that, so without any oracle-like abilities, the issue wasn't 'explained' at the time of writing, hence my comment, but moving on…

    Still not an option. When I say there are only three engineers within 50 miles of me I mean literally anyone with "Rayburn servicing" anywhere on their list of services. I live rurally, so if I can't get what I need from local firms I'm forced to do it myself, whether advisable or not…

    So I suppose a subsidiary question is, in the absence of such "good oil burner or HVAC service technicians", is there a second best option? Buy my own FGA, check some other proxy measure? Anything?

  • Steamhead
    Steamhead Member Posts: 17,380

    @JamesI , tell us where you are located. We might know someone.

    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
  • Jamie Hall
    Jamie Hall Member Posts: 24,849

    A couple of thoughts here.

    First, the hole in the flue isn't put in by the boiler manufacturer — because the flue isn't part of the boiler. It's put in by the installer.

    Now on tuning an oil burner. It is possible to get an oil burner to the point where it will run, and run reliably, by eye. None of us will argue with that. Back in the day it was possible to get a car to run and run reliably by ear, plus a screwdriver and a dollar bill. Does that mean that either one was running as well as it could? It does not. In the case of your oil burner it could be running very well. It could also be running, but poorly and using half again as much oil as it should be.

    Now why aren't there similarly stringent regulations for oil burners as there are for wood stoves and such? First off, there are. It's just that you may never have encountered those sections of the code. The second reason, though, is that pretty much anyone can go down to the big box store, buy a wood stove and some pipe, and put it in their house. That is much harder to do with a boiler. This wouldn't be a problem if the pretty much anyone knew anything about the safe way to install a stove — but, sorry to say it, they don't. So to protect them from themselves we have to have inspectors.

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Mustangman
    Mustangman Member Posts: 113

    I will do my best to explain what I know about combustion which should help you out. Combustion utilizes 2 air sources. Primary and secondary. Primary air is the air you mix with fuel via the air band on the burner. Primary air is in the center of the flame. Secondary air is the air pulled in around the flame for more complete combustion. Oil fired boilers are not air tight nor is the oil burner. A lot of secondary air comes from the oil burner itself by design. Combustion will draw air around the retention head for its secondary air. If its burning and you open a door, you are flooding the fire box with too much air and it screws up the balance between primary and secondary air. Using instruments is the only way to get the balance right.

    I once had a call on a problem boiler. After a short run, the flame would just go out. It made all kind of noise just before it shut down. This boiler had a peep hole so you could see the flame lose its uniformity, got super orange then out. I noticed there was no barometric draft control too. So I put the draft gauge in a hole in the smoke pipe, that I drilled. That tells me, the last guy there did not check draft. I couldn't get the boiler to run long enough to even check it but standing draft with a sort of warm chimney, I had -5. I took the peep hole cover off and fired it up. It kept running and the flame wasn't aweful bad. With in 30 seconds after I put the peep hole cover back on and within 30 seconds.. it was off. Axman Anderson makes a very tight boiler. So at this point I knew the boiler was cutting out because it burned up all the air in the chamber.

    I had my guy install a Barometric and put the analyzer to it. It ran perfectly. I didn't know that in some cases a barometric can provide draft control and a source of combustion air OR the balance of proper draft allows the secondary air to come from the burner around the retention head.

    Hope that helps you understand what happens when you dump an unregulated amount of secondary air into combustion.

    Good Luck

    Steve

    MikeAmann
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 9,378

    I have a feeling that this is what @JamesI might be referring to when he says converted Rayburn.

    and I believe that when @JamesI mentioned an "Engineer" I believe he is referring to an HVAC Tech.

    I also believe that @JamesI is probably located on the right side of the Pond, while most of the answers are comming from the left side of the pond. That being said, the Americans on this side of the pond are probably confusing an oil burner conversion with this type of oil burner

    That might be attached to a central heating boiler or furnace. 

    The Rayburn is an appliance that is usually a "hand fired" coal or wood burning kitchen appliance that is used for cooking.  It also has the ability to heat a small flat so a central furnace or boiler is not needed.  In order to make the hand fired appliance more like an automatic heating system, a gas conversion burner or a wick style burner is used to replace the original equipment grates that hold the solid fuel.  This explains the need to adjust the flame without the ability to see the flame.   Once you open the fire box door, the combustion air will no longer originate through the normal openings.  The combustion air for a wick style burner will accept the combustion air from the open fire door.  


    Here are two examples of the type of conversion burner that a Rayburn may employ that we Americans may recognize.  Not the normal “OIL BURNER” that we are referring to in our American comments.  And we must also consider that @JamesI may not be making “uncalled for” comments.  We must remember that the US and the UK are different countries separated by a common language. That may just be the normal conversation tone in his part of the world.   

    To sum up, in order to be absolutely sure that you have complete combustion, you should drill a 1/4" hole in the vent pipe to the outdoors between the exit of the Rayburn and the draft hood or barometric draft regulator, and take a smoke spot test to see if there is any free carbon particles in the exhaust gas.  That is the best test for complete combustion.  If you have a smoke spot on the test, then you need more air (or less fuel).  

    If there is no smoke spot on the test, then you may be able to close the air down (or increase the fuel).  This second adjustment can be repeated until your smoke test shows a trace of smoke,  at that point you will adjust in the opposite direction until you have zero smoke spot test result. That is about as efficient as you are going to get with that type of burner.  If you need to open the door for some reason, then you will need to close that door in short order, or you risk the incomplete combustion and soot build up associated with it. 

    I hope this helps with your issue and our language barrier. 😜


    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

    CLambbburdPRRGGross
  • JamesI
    JamesI Member Posts: 8

    Thanks everyone for the further comments.

    Yes, I am indeed on the other side of the pond. South-West England. And @EdTheHeaterMan has hit the nail squarely on the head with a picture of my exact Rayburn (minus it's modified oil pipes), with a wick style burner.

    Unfortunately I couldn't drill a hole in the outlet flue as it goes out the back of the flue chamber underneath the old chimney breast, there's no more than about 2 inches of leeway around it. I'd have to drill into the flue chamber itself.

    If that would still work, then a hole and smoke spot tester might well be my best course of action, thanks.

    If it's smoke (and soot presumably) that I'm looking for, then I can check for that even without the hole/detector because - one advantage of being the homeowner rather than a tradesman - I can have a look in the Rayburn tomorrow, next week, in a month etc. By chance the insulation material in the firebox and flue chamber are white, meaning that I can see the slightest soot build up on them. This has happened only once since I've been maintaining it, after a really weird load of puffing and small explosive noises about 5 years ago, I serviced it and the inside was fairly dark with soot. It's never happened since and every time I come to service it, the inside is completely soot free. The restrictor plate in the flue box has a thin dusting of brown soot after about a year (between services).

    At the end of the day I have two concerns of radically different importance;

    1. I'd quite like the Rayburn to be running as efficiently as possible so my fuel bills are reduced, but as long as it's in the right ball park I'm not too fussed.
    2. It's vital that no dangerous fumes enter the house.

    I don't want to confuse the two in asking for advice. Quite happy to set up a system of detectors as per the advice to make sure it's running efficiently, that sounds quite do-able and although a big outlay for the smoke spot detector, it's worth it in the long run, I'm sure. But the most important thing is not what is going up the chimney, it's what isn't (ie what might be coming into the room). Here, I thought, it's FGA or nothing, so I looked up 'the best' on Google and got this result - the Testo 327-1 Flue Gas Analyser. But is says it can check CO (well I've already got an alarm which tests that), CO2, and O2 (presumably to get a ratio?), but only the very high-end ones seem to do any kind of ambient or 'sweep' testing, as the seem to call it, and then only for CO (which I already have a detector for dangerous levels of), and CO2 (which would undoubtedly be impossible to distinguish from the effects of my woodburner).

    The trouble with any of these systems is that unless there is a non-machine way to detect when something might be wrong, then you're faced with either doing a 'sweep' of your kitchen every day in case something went wrong overnight, or testing once a year anyway. It's like suggesting we go the hospital for regular brain scan just in case we have tumour. We don't do that, we go when we have severe headaches which can't otherwise be explained. In other words something human-detectable prompts us to seek the technical gadgetry to find out what's wrong. Either that or we have passive alarms like my CO monitor.

    So I suppose my question should now be limited to what I suppose is the meat of it - what human-detectable 'red flag' should one be on the lookout for that might cause one to call in the experts with the fancy kit to check what's wrong? If there are no such 'red flags', if it's really true that the Rayburn could be leaking dangerous fumes into the house and I'd have absolutely no way of knowing it was doing so without highly technical equipment and training, then I'm screwed. It might go wrong the day after the technician has been and what then…?

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 9,378
    edited April 29

    @JamesI Said:

    "The restrictor plate in the flue box has a thin dusting of brown soot after about a year"

    Brown spot on a smoke test indicates too much air, or a lean fuel mixture when looking at The Central heating boilers with the Power Gun Type Oil Burners. I cant see that ir would be different with a Wick type burner. All the brown stop means is that there is raw fuel that did not even burn because there was too much air and it cooled the flame down so much that the raw fuel (in it's gaseous state) did not even burn a little bit.

    Black soot is from a rich mixture where there is not enough oxygen for complete combustion so some of the carbon only mixes with one oxygen atom making Carbon Monoxide, and other carbon atoms do not mix with any oxygen, making a black carbon smoke that we refer to as soot.

    This is the smoke spot tester I am referring to:

    https://www.amazon.com/Bacharach-0021-0019-Filter-Paper-Sheets/dp/B00I93CAYO/ref%3Dsr_1_1?crid=3E5RJJJFIY0TI&dib=eyJ2IjoiMSJ9.GaVEvqU7eNfsLEo1smfghVgpvi5KhIJlD3rWMiWjQJw3ZTuNBGD4q--ohUBuGLasKPZvM9paZJNqd8BpMP6AJZ7uydQdXcqSTI58IXzEQdlAzuUsddHtzm7QkCLB0Em2.wBJIfSdiFWJK0e0ppPQ6XE8vFasy8LnvhSoyTF6nO3k&dib_tag=se&keywords=Bacharach+True+spot+smoke+tester&qid=1714333263&sprefix=bacharach+true+spot+smoke+tester%2Caps%2C63&sr=8-1

    There are push pins that can cover the test hole when you are not testing the flame adjustment.

    https://www.amazon.com/Pack-Metal-Hole-Plugs-Nickel/dp/B083RDXJWZ/ref%3Dsr_1_1?crid=1O7XXEJWQIA9P&dib=eyJ2IjoiMSJ9.7qGeYxgTCG-uXBL9Wx1KF_t78V88gH9YDKozU3TQO7AX9qTdY2gP3IU6K3R6rwzrMf3GfZEHBt3xgIgk8JILkPeVi-z3ouy6WGByEdcY56G87LZEIxmehbnctklgENtpqAFLMc6QNluaposwSANMVZmnxE8F6LMsm4g0PsRDFCK8-YTYAs_XO5paMoxpwy2pHZ5zgbD5d9YaF5pOolaVw4dia8i14fmxDRwgK4ORkkM.aOCBL53tBratM4fcKAKD84QSjcszEa8t8RW38ye1Fkc&dib_tag=se&keywords=metal+1%2F4+hole+cap&qid=1714335325&sprefix=metal+1%2F4+hole+cap%2Caps%2C80&sr=8-1

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • JamesI
    JamesI Member Posts: 8

    That's really helpful information. Thank you for your time, and patience.

    When it's windy, our Rayburn oven temperature drops from the usual 150 (centigrade) to around 100 which seems a fairly massive drop (considering the oil input is remaining the same), so I could easily see the soot coming from the accumulation of those days over the year (it's windy quite a lot these days), rather than a continuous state of too much air, if that makes sense?

    In either case, a smoke spot tester seems the way forward, so I appreciate the links.

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 9,378
    edited April 30

    When you experience higher wind speed the amount of flow up the chimney increases. You may not believe this but it is actually called the chimney effect. Go Figure  You see Lord Reginold Chimney of Yorkshire discovered it in 1186 AD at Conisbrough Castle.  [1]  

    The faster the wind blows across the outlet on the roof, the lower the air pressure is at that point where the chimney ends high above the roof. This lower pressure will allow the more buoyant hot flue gasses to rise up the chimney faster. In order to reduce the additional air flow on High Draught Days, there is a device known as a Barometric Draft Regulator (or draft control) that you install on the vertical pipe going out of the house close to the appliance. [2]

    Depending on your configuration, that may or may not be easy to do. If a draft control is able to be placed properly on your stack, then you may have more control over excess air during windy days.  That will help reduce the excess air that is causing the brown soot.  

    As long as the oil burner is an approved retrofit for your Royal, Then I would just make the needed adjustment for the least draught conditions - That is on a rainy day with low wind and a relatively warm temperature day - and the overdraught days will do as they do.    

    Footnote [1]

    There is no such person as Lord Reginald Chimney.  But the castle is real and one of the earliest places known to have a chimney in Great Britain.

    Footnote [2]

    installation instruction: check to see if it will work for you https://www.fieldcontrols.com/wp-content/uploads/2019/04/01575700_TypeRC_Rev_B_04-15.pdf

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • CLamb
    CLamb Member Posts: 325

    @JamesI If you are interested in monitoring lower levels of Carbon Monoxide released into the room then I suggest you get a low-level carbon monoxide monitor for the room. We can't call the low-level ones "alarms" in the USA. The one I use is https://www.defenderdetectors.com/ll6170.html . Use of them has been controversial on The Wall.

    @EdTheHeaterMan Regarding wind and chimneys. Cleveland is quite a windy city—even windier in high places. I went to college at CWRU. One of the buildings, Carlton Commons, had a fireplace with the unique design feature that when the front door was opened wind would blow down the chimney filling the room with ashes and smoke. Ironically, CWRU has an excellent architecture and engineering program.

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 9,378

    @CLamb Said "CWRU has an excellent architecture and engineering program."

    That explains the smoke and ash issue.

    A chimney always works to vent the smoke and ash, only if all the parts are configured properly. I don't do chimneys, I just explain how they are supposed to work, and why they don't work when I come across a down-drafting one. Then it is up the the chimney engineer to make the necessary corrections.

    I have always had a great respect for the engineers that design the stuff that works, But for the rest of them, not so much 😜

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

    CLamb
  • JamesI
    JamesI Member Posts: 8

    Cool historical diversion, thanks.

    So, here's what I get so far.

    Getting a clean burn is about getting the right balance of fuel to air. Too much air vs fuel=unburnt fuel, too little air vs fuel=CO etc.

    The restrictor plate cuts down the amount of air drawn in because oil requires less air than wood.

    All well and good so far.

    But the Rayburn has adjustable fuel levels. I can have it on high or low. I can't be reaching into the flue box to adjust the restrictor plate every time I turn the Rayburn up or down.

    So, maybe getting the right amount of air to fuel is done at the inlet - turn the fuel up, let more air in; turn the fuel down, let less air in.

    But then any tests the technician carries out on flue gasses are pointless because I'm left in charge of getting the right air:fuel balance by adjusting the inlet every time I turn the Rayburn up or down, and I don't have a FGA to check I've done it right.

    So, maybe it's not that fine-tuned and so long as the restrictor plate is roughly right I'll always be in the right ballpark no matter what I do with the inlet.

    But the air inlet goes all the way from completely open to screwed tight shut. So that can't be right, I've clearly got the full range of air inlet options, it can clearly be very wrong (no air at all).

    So, maybe don't touch the air inlet once set by the engineer.

    But then we're back to square one. If it's about air:fuel balance then how come I can turn the fuel up, not change anything about the air, and everything's still fine.

    So, maybe there's a wide range of settings that work, as long as I'm not stupid about the inlet. Bit more fuel, no problem, the system will cope.

    But then how could anything go wrong if the air:fuel ratios aren't that fussy? There's two holes (flue and inlet) and they've been roughly the same size for the last 30 years. How can cleaning the Rayburn possibly change either by anything other than a very minor degree which we've just established can't make much difference.

    It just doesn't make any sense to me.

  • bburd
    bburd Member Posts: 1,039
    edited May 3

    @JamesI you have been getting advice from highly skilled, well intentioned people who have never seen a kitchen range designed for solid fuel and converted to oil, which almost don't exist in North America where most of us are based. They are not well suited to our climate.

    Keep an eye on the burner, clean it or have it serviced by a qualified technician as needed, keep a working carbon monoxide detector in the kitchen and be alert for odd smells or signs of trouble.

    Then stop worrying and enjoy your food. 😎


    Bburd
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 9,378

    We need to go back to basics. The fire triangle, you must have all three, if you remove one than there is no fire.

    • In the case of the fuel you have oil, #2 fuel or lighter I would expect, which contains hydrogen and carbon.
    • The oxygen comes from the air in the room where the Rayburn is located. That air has a little more than 20% oxygen and a little less than 79% nitrogen. The nitrogen is inert in the combustion process and just goes along for the ride. Goes in as cold nitrogen and leaves as hot nitrogen.
    • Heat comes from the first ignition source, a match or a glow plug, then the heat is self sustaining after ignition.

    Remove any one and the flame goes out.

    Now look at the numbers:

    In a perfect world this match up of fuel to air would yield a 3000°F (~1650°C) flame temperature.  But the world is not perfect.  So in order to make sure that every Hydrocarbon molecule matches up with an Oxygen atom, we design oil burners to add excess air to make sure there is enough O² in the mix so you get all the carbon to match up to make CO² (Carbon dioxide).  Not enough O² and you find the carbon just heats up and makes black smoke or it mixes with only one oxygen atom and the result is CO (Carbon Monoxide) that is deadly.  So it’s a good idea to have excess air.   

    How much excess air is enough?  If you add too much excess air then the flue gasses leaving the flame kind of water down that 1650° flame to something cooler.  There is all that extra nitrogen and stuff so you may end up with a 1000°F (538°C) flame. With that lower temperature flame, the gasses that heat up the heat exchanger or stove will be much cooler.  If you don't add enough then you get soot, and CO.  

    This is why you don’t want too much excess air but you want enough.  Each oil burner has its own minimum and maximum based on the conditions.  Also adding too much air is less dangerous than not enough so, burner manufacturers like to err on the side of caution.   That said, you, the consumer of the fuel, pay the price for the inefficiency.  

    Example of a 80% efficient flame

    You can clearly see from the numbers that just adding 50% excess air (a normal amount for a gun type power burner) the flame temperature drops to under 2500°F (1338°C). the same amount of BTU per pound of fuel but it is spread across more air. That extra air cools down the flame, and since the space inside the heater does not change when we add more air, The cooler byproducts of combustion take up more room so they race thru the heat exchanger faster. since the hot gasses are moving faster thru the stove, they have less time to exchange the heat to the other side of the stove. This may even end up with a higher exhaust temperature. Lower start temperature + higher exhaust temperature = less efficient operation.

    By this illustration with 50% and 150% excess air, you get two different flames,  iI the amount of flue gas goes from ~22 pounds of flue gas to over 50 pounds of flue gas,, and the space inside the heater stays the same, then that gas needs to race thru the heat exchanger at more than double the speed, to get out of the way for the next batch of flue gas to travel thru.   So extra air will cost you more to operate.  Less heat stays inside the home.

    With a wick type burner, I can only guess that the combustion air requirements are over 100% excess air.  That may end up with a much colder flame.  Once you get the stove’s fuel air mixture where you want it to be, you may want to understand how draft and fuel level adjustments can be adjusted for the conditions you encounter.  

    • Do you want to test when the draft is at the highest with the flame set low, and also when draft is the lowest with the flame set high?  Yes.
    • Do you want to remember to adjust the air for optimal efficiency when the excess air may cause that brown deposit to form? Maybe.
    • If you do that adjustment, will you remember to put it back after the high draft condition is over? That is up to you.  

    I hope this condensed lesson in combustion theory is helpful.  (in my one day seminar, this portion of  the discussion takes about 30 slides and 48 minutes.)


    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

    LRCCBJ
  • JamesI
    JamesI Member Posts: 8

    @EdTheHeaterMan it restores my faith in humanity that people are prepared to put so much work in for free to help others just because they asked. That's been very helpful.

    @bburd I think you're right. The thing is, there is a smell which is why I've been fiddling and trying to work out what's wrong. Fortunately, the smell is on the outside (we can smell it in the garden occasionally coming from the flue outlet). The smell is distinctly that of heating oil.

    With the help of Ed's exhaustive information, I'm pretty sure I've been barking up the wrong tree with the whole air:fuel balance which I assumed was wrong. I'm now convinced the problem must be the burner itself.

    If I'm getting smells of unburnt fuel, then, according to Ed's explanation, I'm giving it too much air for the fuel.

    But, the air inlet, restrictor plate and flue are all the same as they've been for at least 30 years. I assumed it must have been some tiny deviation from those settings that's caused the problem, but now I realise those settings simply can't be that fine-tuned otherwise everyone would muck them up all the time when they turn the heater up or down.

    So the only explanation left is the only other component in the system - the burner. Since I've checked the oil delivery rate is per specification and I've checked for oil leaks, it must be that the flame is not hot enough for the oil, but not because of air, because of something else…

    … and there I'm at a loss, but as you say, if the problem is the burner, then I literally need a specialist in that exact type of burner to provide some ideas. Back to hunt again…

    EdTheHeaterMan
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 9,378
    edited May 6

    #2 fuel burns with a specific smell at the exhaust. wether it is #2 fuel in a diesel engine or #2 fuel in a pot or wick type burner, or #2 fuel in a power gun burner, the exhaust smells very similar. Since I have worked on oil burners for over 40 years, and some of those years were in the later 1970s when fuel prices jumped rapidly and alternate heating devices were popular, I remember having the KeroSun® brand space heater in my own home for a year. Whenever the tank ran out, the exhaust from that heater was very offensive to me. Maybe because I had to smell it all day and I just didn't want to smell it a home when trying to relax.

    Since that smell is always there perhaps the location where you smell the fumes is the issue. This illustration shows how the same venting pattern can be offensive in one case where it is not in the other case. It is just going to happen, and no adjustment will make the smell any different.

    This next illustration may be an occasional problem based on weather conditions and wind direction.

    How to go about solving this problem depends on how severe the problem actually is.  And some adjustment to the flame will make it more efficient. I can say from experience that a rich flame odor is very different from a lean flame odor, but the odor is still there.  The unusual north wind illustration is a barometric pressure problem that causes the flue gasses to cool down enough to become heavier than the surrounding air, bringing that odor down to ground level.  So when you notice the odor, take note of the weather conditions.  See if they are consistent each time you smell the fumes.  Humid, cold, dreary kind of day may be what I’m talking about.

    There are many other things that can happen to those invisible fumes.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

    CLamb