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Downfiring Boiler

68GMC Member Posts: 36

I own a Burnham IN6, I would like some knowledge and direction on downfiring the boiler. <a href="http://www.heatinghelp.com/forum-thread/129549/Oversized-Boiler">[url=http://www.heatinghelp.com/forum-thread/129549/Oversized-Boiler]http://www.heatinghelp.com/forum-thread/129549/Oversized-Boiler</a> 

I'm pretty sure I did the math right, <a href="http://www.heatinghelp.com/forum-thread/124807/EDR-calculations-for-steam">[url=http://www.heatinghelp.com/forum-thread/124807/EDR-calculations-for-steam]http://www.heatinghelp.com/forum-thread/124807/EDR-calculations-for-steam</a>, this post goes through pretty much the same thing, although theres was a new installation. I believe my boiler is around the 8 year old mark. Rod was kind enough to point me over here, it sounds like I should be able to have a gasfitter install a IN5 burner nozzle to essentially make my boiler smaller.

Is a burner nozzle the same as the burner orifice? How do I explain to the gasfitter what I am trying to do? Any rough ideas what this should cost? I'm up here in Ontario, Canada, so I can't use the "Find a Pro" thats on here. Rod suggested I should definately not attempt this job myself, right?

Thanks everyone.



  • Tim McElwain
    Tim McElwain Member Posts: 4,593
    I am on the way out of the

    office but will get back to you on this. Right off the bat I do not recommend downfiring boilers and I will explain later why!
  • Tim McElwain
    Tim McElwain Member Posts: 4,593
    I am assuming this is a gas boiler

    based on your questions. The boiler at 175,000 BTU's (if all your calculations are correct) is way too large. I do have some questions that may answer why:

    1. Did this boiler at one time provide or does it provide domestic hot water? If not to take advantage of some of that BTU you may want to consider an indirect water heater.that would be able to use up some of the BTU you have.

    2. Have any radiators ever been removed?

    Now as to down sizing, to down size this boiler it would have to be drastic and that would definitely affect combustion efficiency. The boiler heat exchanger and combustion chamber are sized to work best at full input which in your case is 175,000 BTU's.

    Orifices are not the same as nozzles for oil and typically there is an orifice for every burner.

    I would have a professional come in and do a heat loss, recheck your figures on square feet of radiation. Clock the burner to determine its exact input and also check gas pressures. They should also do a combustion test to determine if you are firing at maximum efficiency.Then they can advise you on alternatives.

    Please contact me by e-mail as I want to hook you up with a Rep from Burnham to advise you on this boiler and what they may recommend.

    My e-mail address is [email protected].
  • 68GMC
    68GMC Member Posts: 36
    Oversized Boiler

    Sorry, I should have clarified it is a gas boiler. I believe I have all of the original rads, there was one loose when I moved in but I repiped it in last winter. I believe based on the floorplan of the house it originally was an 8 room house, 4 per floor, and had one rad per room. I am planning on adding in one small rads on the third floor this summer, but that will only increase my rad square footage by 20 sq. ft. or so.   

    I have thought about the small water kicker idea, but I was talked out of it given the reasoning that I don't want/need to be running a 175000 btu appliance in July to heat water. But I do agree, it seems redundant to have a 175000 btu boiler running right next to a 36000 btu gas water heater. Would there be a way to run a seperate heating loop off the boiler to a hot water rad in the basement, or a small kicker heater?  

    I am confused, when I do the math, my current setup requires around 80,000 btus to perform. Do you try to match that number to the input or the output of the boiler? It made more sense to match it to the output, because that is how much load the boiler can produce....correct? If you have anywhere to direct me to read up on this, I would appreciate it.


  • Tim McElwain
    Tim McElwain Member Posts: 4,593
    You match the output

    of the boiler to the heat loss/square feet of radiation. You could have the water heater set up to be a storage vessel for the winter and then switch over and use just the water heater in the summer. A good professional could do that for you very easily.
  • Roland_18
    Roland_18 Member Posts: 147
    Downsizing Boiler

    A couple of years ago, I spoke with a Burnham rep. who was a regular on this board.

     I have the same situation, too much boiler, not enough radiation. The Burnham rep said I could go down an orifice size but it would not gain me much in savings.

    What would be the result of removing a burner tube or two and blocking the open orifice ports in the gas manifold? This way there is no disturbance of the remaining tubes combustion.
  • Tim McElwain
    Tim McElwain Member Posts: 4,593
    It is never a good idea

    to plug off burners and remove them it will just take longer to heat up the unfired sections. It also does not change the amount of excess air being brought in so the combustion efficiency goes down even further. After 50 years of working on thousands of gas boilers and furnaces and testing them for combustion and thermal efficiency you actually lose more than you will ever gain.

    In the 1980 and 90's AGA (American Gas Association) conducted testing across America on various energy and efficiency procedures. De-rating proved without exception to actually increase over all cubic foot consumption. Most of these tests lasted two years. Just as a point of interest the most efficient additions were insulation and new windows and sealing up air leaks. Those were also the cost effective as far as return on your investment. 
  • 68GMC
    68GMC Member Posts: 36
    Had a gas tech

    come out yesterday and do everything you suggested. Clocked the meter, it was around 180,000 btu. He turned down the pressure and reclocked it. He did an efficiency test as well, the numbers were pretty much the same as when he did it 2 1/2 years ago, CO2 went down a little, O2 went up a little, and the "t stack degrees fahrenheit" went up about 20 degrees. So I doubt I will see a huge change from this alone, but if nothing else it's running a little leaner.

    He said there is nothing you can do except wait until the boiler is worn out and go smaller, but he did say most boilers he installs are half the size of the one I have for the same size homes. It's no the answer I was hoping for, but at least I know mine if running the best it can, and it doesn't sound like it being oversized is dangerous at all, it's just hard on the monthly fuel bill.

    Thank you again for your patience and advice.
  • Tim McElwain
    Tim McElwain Member Posts: 4,593
    If he reduced the pressure what was it when he

    started? Most gas valves are set up to operate at 3.5" WC outlet pressure. Reducing the pressure is just as bad as changing orifices you have accomplished NOTHING!

    If the CO2 went down and the O2 went up and the stack temp increased then you have lowered the operating efficiency of your systems. You have accomplished NOTHING!

    I would be interested in knowing what his readings were before he reduced the pressure and then what they were after the reduction.

    The fact that he lowered the gas pressure can cause other problems. So here is my final question. What was the O2 reading and what was the CO (Carbon Monoxide air free reading) and what is the net stack temperature. Those three things will determine if the system is operating efficiently and might I add SAFELY! Why do I say that, very simple what he did (reducing pressure) can cause your CO air free in the stack to go over 100 PPM or higher.
  • 68GMC
    68GMC Member Posts: 36
    Test results


    351.9. degrees F T stack

    7.08 %CO2

    83.1 EFF

    8.3 %oxygen

    1 ppm CO

    2 ppm Undiluted CO

    78.6 degree F ambient air

    82.9 Instrument Temp

    Yesterday, 2010

    371.4 degree F T stack

    80.9 %EFF

    6.12 %CO2

    10.0 %oxygen

    1 ppm CO

    2 ppm Undiluted CO

    81.3 % ExAir

    61.4 degree F Ambient Temp

    54 degree F instrument temp

    I do not know what the pressure was before or after he adjusted it, on the front of the boiler is a Honeywall control above the burners, with an on/off like the control for a hot water heater, all he did was clock the meter, go inside and turn a flathead screw on the Honeywell control, and go outside and reclock the meter. Said everything was good. Said before I was running 180,000 btuh, and after he adjusted it I assumed it was clocking 175,000 btuh.

    Does that make sense to you?
  • Tim McElwain
    Tim McElwain Member Posts: 4,593
    I have a little problem with

    some of those readings, in particular the CO air free is extremely low in both sets of readings, it is almost too good to be true.

    The 10/01/2007 83.1% efficiency does not match up with the O2/O2/stack temperature my calculations show with those readings the efficiency would be 79%. To get 83% the stack temperature would have to be 250°F which would be causing condensation in the flue system.

    The Feb 2, 2010 CO2 and O2 readings are actually out of sync with one another. However lining them up as best I can with my charts the 80.9% reading is not correct it should be 77%. The CO also very low.

    If you are satisfied I guess we are all done but I am not sure you will see any change in cost to operate.
  • 68GMC
    68GMC Member Posts: 36
    I wouldn't say I'm satisfied

    but those numbers mean nothing to me. I understand the basic basic concepts of combustion, and I understand that there must be some exhaust temp and unburnt fuel and air. It's the kind of thing where I want to give you more information but I don't know what else to give you. Rick, the technician from ******* Plumbing, is apparently one of my towns only steam guys, I've used him off and on for almost three years. Glenn Stanton suggested John Raymond at Hydronic Systems Canada, who referred me to Hydronic Solutions in my hometown, who suggested ******** Plumbing, where Rick works. (Did you follow that?)

    I can maybe find out the make and model of the efficiency tester, and I can call another company to come in and do another efficiency test, if it's another efficiency tester. For right now I'm at a loss on how to give you more information to help you help me.

    I talked with a friend of mine tonight, Bob, who's a small engine mechanic. I said it reminds me the customer who comes in and says "my snowblower won't start".  Bob says "is it getting fuel?". Customer " i dunno". Bob: "is it getting spark?". "I dunno". Bob "What have you tried?". "I pulled the cord... it won't start".

    That's how I feel.... you can ask me all the technical questions you want about why the CO2/O2 levels don't match the stack temp and I'm going to come up with "I dunno".  If you can suggest a book to read up on I would look into it, I couldn't find one tonight.

  • 68GMC
    68GMC Member Posts: 36
    WOHLER tester

    I had a different company come out for a service, while here the tech diagnosed a faulty gas valve on the boiler. He explained to me that the gas valve was stuck open, which could result in an explosion, somehow instead of lighting the pilot, a pause, and then the pilot lighting the main burners, the way it was running the pilot and main burners would light all at once. He changed the gas valve and set up the pressure on the valve using a water column, he said 3 1/2" of water column was the right gas pressure for the boiler. He also performed an efficiency test using a Wohler tester.

    02  7.5%

    CO2 7.5%

    CO air ppm  0

    Stack temp  413 degrees

    Ambient temp 32 degrees

    Efficiency 79.1

    He explained that because the tester was cold, it read the ambient air as 32 degrees F, that the real efficiency would be a little lower, probably around 75%.

    Is that more in line with what you would like for performance?

    Thank you.
  • Tim McElwain
    Tim McElwain Member Posts: 4,593
    That was a good catch

    on finding that problem with the gas valve. It tells me the technician knows his/her stuff. You may want to have that technician check and see if the valve manufacturer would make good on the defective valve. Sometimes there are recalls on controls which also include a rebate for parts and labor.

    The readings look good and resetting the pressure to 3.5" W.C. is a good move. You as I am sure you know have a boiler too large for the system. The only solution to that is a new boiler.
  • alcraig
    alcraig Member Posts: 28
    edited February 2010
    optimum combustion

    If he can lower his stack temp and increase his efficiency % with a lower firing, assuming he can keep his o2 co2 and co levels within a safe range, then I have to think he's going to waste less fuel. With his new setting, he's sending more heat out the chimney. If his old settings resulted in higher co levels, I can see the benefits of this readjustment. But please explain why he needs to add more fuel to the mix just to send it out the flue. Yes, it's a better burn, but it's also more fuel expense with no adverse levels resulting.

    Ideally, if he could adjust his air to reduce the o2 while reducing the gas pressure, then he would get the best of both worlds (optimum combustion and less fuel wasted)

    And btw, I didn't think you could trust a cold tester...it's results could be off, no?

  • Mike Kusiak_2
    Mike Kusiak_2 Member Posts: 604
    Lowering the firing rate

    If he could reduce the firing rate while also reducing the excess air, then he might see an increase in efficiency. The problem is that reducing the gas pressure will not appropriately reduce the excess air with an atmospheric boiler. The geometry of the burners, jacket and the size of the flue passages pretty much determine the amount of combustion air. So with lower gas pressure, the amount of excess air increases, thereby reducing the flue gas temperature. The flue temp decreases, but not because of increased efficiency, rather because the flue gas is being diluted by more excess cold air.

    It would be a different story with a power gas burner, where you could adjust both the gas an the air for optimum combustion at a lower firing rate. Here you could actually see an increase in real efficiency at a lower firing rate.
  • 68GMC
    68GMC Member Posts: 36
    Downfiring isn't doable

    According to Mr McElwain, downfiring is not doable, practical or recommended. As stated above, the boiler is designed to run on 3.5" WC gas pressure, and downfiring would result in an uneven combustion temperature and could create more problems. Apparently it came from the factory this way, and should stay that way. We agree that the boiler is oversized, and the best I can do is to make sure my boiler is running at the best efficnency I can get out of it, if I want to lower my gas usage I need a smaller boiler.

    As for the gas valve, it was the fastest diagnosis of any problem I have ever seen. I had wanted the tech to come in to help me cut and thread some 3" pipe, and had a couple other questions for him while he was here. About a month ago, when I had the boiler jacket apart, I noticed a jumper wire on the control box. From a mechanics background I know jumper wires are bad, there is a factory wiring harness on appliances/vehicles for a reason. I asked him about the jumper wire, he said my gas valve is bad, explained why it was bad and then pulled a wire off the gas valve as the boiler was running. I assume an operating gas valve would should off the boiler without power to it, as the valve would shut automatically.

    Any suggestions on a book or reference manual I could purchase to learn more about this? I am not interested at all in doing gasfitting, but this is an area I know nothing about, and at the very least would like to be a better educated homeowner so I know I'm not getting taken advantage of.

    By the way, the first company uses Testo analyzers. I doubt there would be a difference between Testo and Wohler, but is one better than the other?

    Thanks all.
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