Downfiring an oil burner

realolman

do you explain it. The analyzer's efficiency calculations do not enter into it. What I use the analyzer for is to set the fuel / air mix for each size nozzle.

I have monitored the results. It's not that difficult. There is no mysterious phenomenon. It's really quite straightforward.

The burner uses less oil per hour of running time. That's a function of the nozzle's construction and the pump pressure.

The running time has not increased to offset the decreased oil usage. I have it monitored and recorded.

The stack temperature is lower. I have a thermocouple in the stack

The CFM up the stack is less. I have installed a low fire baffle, static plate , and retention ring.


I have tracked the outdoor temperature to be sure I am comparing similar degree day's oil usage.

What do I not understand that I need to be taught? Again... condescension is not proof.

Kyle_5

Downfiring an oil burner

Several years ago, when oil was less than $1/gal., I ripped out my old scorched air system with it's cracked heat exchanger, and put in a hot water boiler with radiant floor heat. I also scraped the electric water heater for an indirect heater from the boiler. At the time I was planning on a large addition to the house which hasn't happened yet so the boiler is a bit oversized for the current house. Also, during the summer it is running for just the hot water. So with the price of oil approaching $4/gal. I am wondering if I can downfire the burner a bit to compensate for the boiler being oversized. The burner has the .85 gph 45degree B nozzle that the boiler calls for and I am wondering if it would be of benefit to maybe change to a .75 gph nozzle or maybe even smaller? If I do, do I need to change any of the other factors?

Thanks for your help.

Robert O'Brien

Yes

but it has to be done by someone with an analyzer who knows what they're doing

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Long Beach Ed

Yes again...

The reason Robert said it must be done by someone who knows what he is doing is very important. The efficient and safe combustion of oil requires the proper ratio of air to fuel.

When you change the nozzle you must also change the air setting of the burner.

Failing to do this will cause improper combustion which could waste oil, or make lots of smoke. Smoke soots up the boiler and will sooner or later clog it. When the passage to the chimney gets clogged, the smoke "puffs back" into the room.

That can destroy your home and produce carbon monoxide amounts that can kill you and your family.

Professionals use instruments to set the air and calculations to figure the proper nozzle size.

Anyone who fails to do that is incompetent, ignorant or lazy and dangerous.

Paul Fredricks_5

Also

Some manufacturers recommend not down firing their products. I've seen down fired boilers where everything checks out fine, but the CO level is way high. The solution was to fire it back up to factory spec.

Got to use a combustion analyzer.

George Endres

overfired boilers

If over fire is giving you short burner runs, have you tried increasing the heat differential--like the Beckett Heat Manager does, or otherwise like I did.

I have already re-jiggered the L8124 controls to get a 34 degree heating run differential (3+ times what the Honeywell normally allows), but there is still just too much flame to obtain reasonable burn periods in this tiny home.

Even keeping the extreme differential, I need a rate something closer to .5 gph to get reasonable. Can this be done with a clean burn? Or how badly will I screw things up trying?

realolman

I downfired mine

I think from a 1.1 gph to a .65 on several tries. I have a combustion meter. no way could I have done it without it... you just don't know otherwise... and there were times after putting in the low fire baffle that you simply don't have the air to spare.

Run times were too short and the stack temp was way too high. It still grieves me to run as much hot air up the stack as I do even now.

On the suggestion of one of the guys here I disconnected the one zone from being able to call the boiler for heat. That helped a lot.

I installed a beckett heat manager... it spread the differential out from 10 to 27 degrees.

K HAYNES

YOU CAN DOWNFIRE A BOILER. AGAIN AS SAID YOU NEED A COMBUSTION ANALYZER TO DO IT PROPERLY. SOMETHING ELSE THAT HASN'T BEEN MENTIONED IS STACK TEMP. YOU HAVE TO KEEP THE FLUE GAS TEMP ABOVE THE CONDENSATION LEVEL. .85 TO .75 NOZZLE ISN'T A LARGE CHANGE. I DON'T REALLY THINK IT WOULD BE WORTH THE EFFORT. I HAVE DONE THIS TO MY HOME BOILER WITH A COMB ANZ. I WENT FROM A 1.30 @ 100 PSI TO A .95 @ 140 PSI. THIS WAS IN AN OLD STEAM BOILER . MY STACK TEMP STILL STOOD AT 488 DEGREES WITH NO CYCLING PROBLEMS. WITH A NEWER BOILER THEY ARE EFFICIENT ANYWAY . I WOULD ADJ MY WATER TEMPS AND SEE IF THAT WORKS

realolman

Quit yelling

I'm hard of hearing , but not hard of reading


I mentioned stack temp in the post before yours.

I went from 1.1 to .65 and the stack temp is still 538°.Burnham v74 clean as a whistle fire side and water side.

I'd like to know what you'd have to do to lower the stack temps down to condensing range...

Jim Davis_3

Underfiring any equipment below its rating will normally cause an increase in fuel usage not a savings. This is usually a bandaid when someone can't get the burner to run correctly at its normal firing rate. Controls setting and boiler reset is the only proper & efficient way to de-rate equipment.

Robert O'Brien

J

> Underfiring any equipment below its rating will

> normally cause an increase in fuel usage not a

> savings. This is usually a bandaid when someone

> can't get the burner to run correctly at its

> normal firing rate. Controls setting and boiler

> reset is the only proper & efficient way to

> de-rate equipment.



Jim,do you have any non-anecdotal evidence to support this claim?Because my opinions are based on anecdotal observances,not scientific data.Convince me I'm wrong.

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Gordy

Down firing

It would seem to me that even though you are down firing your heat source, you still are trying to heat the same mass of the HX to achieve the same water temps. A btu is a btu,and mass is mass, you are only taking longer to heat the mass after down firing.

Band aid to poor design is correct. Saving equipment cycling is all that is being achieved here. I don't see any efficiency gains in longer burn times do to down firing. In fact efficency may decrease do to the longer run time of the circulator or circulators in the system.

JMHO Gordy

Jim Davis_3

I worked with a lot of energy auditors, contractors, engineers back in the 80's during the energy crunch when the government was giving 50% rebates on all energy management spending. It didn't matter whether it was oil or gas, if the equipment was operating less than its rating it showed a higher energy bill. In one case a furnace was fired with a 1.25 nozzle although it called for a 2.00 nozzle. The furnace was oversized but that doesn't change the rules of heat tranfer and thermodynamics on the fire side. When it was fired back at the 2.00 rating it did cycle more often because it heated the house much quicker. The homeowner noticed he had heat coming out of registers he never felt before. But what excited him was that his oil usage that winter was 600 gallons less than any of the previous 15 years he had lived in the house. Odds are in 15 years you would have two similar winters so thinking that this was just a mild winter would be wrong.

100% of all appliances that I have tested for the past 30 years used less energy when their firng rates were brought up to their maximum capability. Firing at 60% versus 100% on the average used 25% more fuel regardless of the conditions - residential, commercial and industrial.

Live/Learn

down firing re-visited!

Hi Wallies, I asked this question awhile back and got all kinds of ideas on both thoughts . Larger nozzle size (shorter run time) or smaller nozzle ( longer run times). Which method will save the most oil? I'm more concerned with saving oil then I am with burner efficency. Some say a burner should fire through the whole heating cycle for the best efficency. Seems like efficency and economy are two different things in this case. Please educate me! Thanks, Live/Learn

realolman

I looked

at my records and I was mistaken in my earlier post:

This is a burnham v 74

Before I started I had a 1.1 gph nozzle and the stack temp was 620°

Now I have a .65 gph nozzle and the stack temp is 456° ( which still grieves me )

Also I put a on a low fire baffle, static plate, and retention head, so while I don't know what the CFM up the stack is, I do know it is less than before, because I can't set the burn very lean at all... there just isn't any air left. so I'm putting less CFM up the stack at 164° lower temperature.

.

I don't see how downfiring a boiler could be less efficient than not downfiring it. Is it less efficient than a smaller boiler? ... that I don't know...

but I think if I could put more surface area of heat exchanger on the stack at end of my boiler, I could extract more heat from the combustion gasses. It seems logical to me that the larger heat exchanger of the V74 might possibly be extracting more heat from the lower BTU flame than a smaller boiler could.

Brian_18

WOW, I'm scratching my head now

Just to make clear I am NOT a pro, but make the following observation. I have a low mass boiler, which according to the installation manual is mulit-rated for 105, or 140, or 154 thousand BTU/Hr. The ONLY change to do this is nozzle size, and the appropriate burner set-up. It has been set-up at the lowest rating, as it matches my load best. Am I to believe that it will run more efficiently, using less oil per season set up at the highest rating? Even though it will short cycle all the time? I thought short cycling, and oversize boilers were energy hogs? Help me understand, Please !

Gordy

Different situation

Than a boiler that does not have the sizing option as yours does.

Jim Davis

The easiest way to explain underfiring is place your hand a few inches above a candle flame. You feel it getting warm or maybe hot if it is a big candle. Now move the candle farther from your hand. Some will tell you your hand will still get warm, it just takes longer. Ever notice when sitting next to a camp fire you don't stay warm when the flame gets smaller not matter how long you sit their.

Low flue temperature does not necessarily mean high efficiency. It just shows that the heat produced dissipated somewhere. Small flames produce low volume of gasses to scrub the entire heat exchanger surface and that is not affective.

Believing that combustion efficiency calculations give you any actual valid data is absolutely wrong! It is kind of trying to tell time with a broken watch. It does have the exact right time twice a day but you don't know when.

Oversized equipment causes minimal efficiency loss whereas underfiring causes maximum. The more you underfire the worse it gets.

Weezbo

just had a similar conversation yesterday .

efficiencies ,& effectiveness has probably been the main down fall of 90 % of all heating systems in the entire world.

"like a broken watch it is somewhat helpful
because at least it has a possibility of being right when you look at it" *~/:)

Steamhead (in transit)

The problem seems to be

that so much equipment is way oversized. This results in short-cycling and more wear on burners, controls etc. On oil burners that do not have valve-on delay, the starts and stops can be rather dirty, so short-cycling can result in more sooting.

A properly-sized unit doesn't have to be downfired.

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realolman

I agree

with what you said about the candle and campfire, however being out in the open atmosphere is not analogous to a boiler.


Moving your hand away from the candle makes the constant area of your hand a smaller part of the total area into which the total heat from the candle is transferred. I would guess exponetially so.


In the case of downfiring a boiler, to where is the heat from a smaller BTU flame dissipating, if not into the water, or up the stack? My stack temp is lower and the CFM up the stack is also lower.


Wouldn't you agree that if I constructed some sort of additional heat exchanger ( made my heat exchanging area larger ) to replace my boiler's breeching I could extract more heat from the gasses that is now escaping up the stack?


I suppose the temperature at the heat exchanger wall might be lower with a smaller flame, but I wonder how much? What is the difference in temperature at the heat exchanger wall in a Burnham v74 with a .65GPH nozzle vs a 1.1 gph nozzle, both set with an analyzer?


I don't know how meaningful the efficiency calcs. on my analyzer are. So far as I know, my analyzer is made by knowlegeable people. It measures the temp of the combustion air, the stack temp, the Oxygen content of the combustion gasses, and displays the efficiency. What does it mean?


It doesn't make sense to me that downfiring an oversized boiler is less efficient than not downfiring it.

Considering the boiler, you can :

1. downfire it

2. not downfire it


I guess you could up fire it if you were so inclined.



If you don't downfire it, it seems there is only one
logical result:

1. Your oil usage will remain the same.
..



If you down fire it, one of three things will happen:


1. overall oil usage will increase


2. overall oil usage will stay the same


3. overall oil usage will decrease

My oil usage has gone from 4.25 Gal. per day @ 31.8° to 2.91 GPD @ 31.7 ° To be honest, I have also installed a beckett heat manager, and done some other things, so downfiring the boiler is not the only variable.


I have done considerable monitoring of my boiler over the past two years. I like everything about downfiring it better than before... It fires smoother, runs quieter, stack temps are lower, and most importantly, it uses less oil. No way would I go back to a larger nozzle.

Bruce Stevens_2

Much of the heat transfer

is via radiation in the chamber area, so the smaller the flame is the less radiation effect there is in the chamber, which does not get taken into effect with you flue gas analysis. Pin style boilers used to say downfire up to 10- 20% depending on manufactuer, todays triple pass manufactuerers say up fire up to 10% but never down fire. so one must be a bit more carefull in what we do when getting away from factory specs.

[Deleted User]

save on oil

You can def down fire an oil furnace or boiler if it is oversized (AND YOU HAVE TO HAVE A PRO WITH A COMBUSTION ANALYZER DO THIS, IT IS A MUST!!). You need to be sure it's oversized though. In many areas such as the northern area where I now reside. Boilers are sized according to the coldest winter day. That's where outdoor reset controls and or a Becket Heat manager come into play. There is even a newer control put out by Intellidyne, they are the ones who made the Beckett Heat Manager, so it has the same easy wireing. The big plus of the intelidyne (which I picked up for a great deal at North Conway Winnelson) is it allows you to see your savings/customers oil savings on a screen, and you can also dial down and control an inderect with the same control, so bigger savings if you don't have tankless.

realolman

Could you

please explain where the heat, radiated or otherwise, goes? It can't just disappear. It's in the boiler.

I have monitored my boiler for two years, and recorded the outdoor temperature. As I have mentioned, I have also done other things, which would cloud my water somewhat.

Are you telling me that if I replace the 1.10 GPH nozzle from my present .65 GPH , I will use less fuel, even though all my monitoring says otherwise?

I'd like to see something more substantive to support that opinion.

Jim Davis

The only proof I have is thousands of residential, commercial and industrial customers that saw their usage drop substatially when their firing rates were brought up to the maximum. 600hp boiler, oversized firing at 200HP. Raised firing rate to about 500Hp(couldn't get to 600HP because it wouldn't run for more than two minutes) and the gas bill drop over $100,000. 400HP modulating boiler eliminated modulation and usage dropped from 33,000,000 cu.ft. to 22,000,000 cu.ft. Eliminated low fire on 100HP boiler and saved $35,000. Eliminated low fire on 2-stage furnace and bill dropped 40%. Energy auditor calculated that a 2-stage boiler was using more fuel in Spring and Fall on Low Fire than it was during Winter in Hi fire. Given the same combustion settings firing close to the maximum will save money. Controls can be properly set to minimize cycling.

Smart people make combustion analyzers but the calculations were conceived by someone that might not have been. No manufacturer of combustion analyzers would tell you their calculations are accurate if they are intelligent.

Example: Maximum efficiency = 100%
- 14% H20
- 6% O2
- 12% Flue T (430 degrees)
68% actual efficiency but analyzer will calculate somewhere around 77-78%.

realolman

In all of that

about thousands of residential and industrial customers and $100000 drops in gas bills, there is not one shred of proof.


You're saying that in properly set up modulating gas fired equipment , you would save fuel by running it wide open only.


All the outdoor reset and modulating is for nothing but to raise your fuel bill?!?

How foolish of people to make and buy this stuff!

In my oil boiler in my house, which I have been monitoring for two years, I am saving fuel by using a smaller nozzle.

realolman

In all of that

about thousands of residential and industrial customers and $100000 drops in gas bills, there is not one shred of proof.


You're saying that in properly set up modulating gas fired equipment , you would save fuel by running it wide open only.


All the modulating is for nothing but to raise your fuel bill?!?

How foolish of people to make and buy this stuff!

I apologize for being a smart aleck, but I feel pretty confident about my own experience which I have been working on for many years.


This is what I am basing my oil burner downfiring opinion on... I made a computer program and bought some hardware to monitor my boiler. It connects the computer to the boiler through solid state relays and sensors that monitor temperatures.


Among other things, it creates a list of times when the burner came on and when it went off. It is a relatively simple matter to figure out how much oil I used in a 24 hr period and the outdoor temperature.

I can plot this on a graph and compare it to what it was before I make some sort of change... like downfiring... Or in the case of what I have attached, I did not use the setback thermostat for one day.

I have been monitoring it for two years. I know I am using less oil after downfiring the boiler.

On one hand people are encouraged to use analyzers, and then on the other, someone says they are inaccurate. I don't know about the accuracy of the analyzer in calculating efficiency... I have always felt that there needs to be some connection to the rise in water temperature to determine boiler efficiency. I have felt that they were just reporting combustion efficiency, since they could be used in other combustion equipment besides boilers. I truly don't know.

Jim Davis

I have spent the last 30 years studying this in the field. Very little was ever written on how to actually run things correctly. I wasn't paid to do a study, just help people run their equipment safe and efficient. And the purpose of modulation was never efficiency. I just tested a Cleaver Brooks boiler and the flue temperature was 190 degrees with 180 degree water in it. The analyzer said it was 86% efficient. Surprised it ever heated the building. There is a lot to this that you have never been taught and it is easy to misunderstand. Many manufacturers have tried to prove that I am wrong about the modulation and 2-stage but somehow can't seem to do it. Not trying to prove or disprove anything, just reveal the truth as it has occurred in the field. Plenty of techs on here have been to my training and have yet to uncover anything different. If you are saving money it is not because you are underfiring.

realolman

Hey

Don't give up on me now.

I want to know what I'm doing wrong. I imagine there are plenty of others who want to know why their fuel usage will increase by installing a smaller nozzle in an oversized boiler.

I did this to my mother's as well, beacuse I thought I was helping her.... if you're going to tell me that she is paying more for fuel because of my misguided good intentions , I think it's only fair you see this through to a reasonable conclusion. I'm not unteachable... I can learn.

I am tracking the time my burner runs and I know what the nozzle's flow rate is.

If the time the burner runs does not increase enough to offset the higher flow rate, why am I not using less oil?

Long Beach Ed

Interesting...

This is a very interesting and not often investigated topic...

I can understand how, especially in a steam boiler, a flame that is too small can result in slowing the rate of boiling to such a point that it is counterproductive.

Like many, I have had good experience down-firing a boiler that was too large or that may have been piped incorrectly. The lesser steam velocity helped the system operate better.

But how small is too small? Many manufacturers do not specify a firing range and probably don't test for any range other than the single nozzle specified.

Jim Davis

Not giving up and it sounds like you are quite open minded. In class I have shown people how I took two pipe nipples 1-1/4 & 1-1/2 and put the same flame in both of them. The 1-1/4 got really hot while the 1-1/2 stay fairly the same temperature. Radiant heat is the most effective method of heat transfer. You get 7 to 8 times more heat from the flame than the gasses it produces. Make the flame smaller and it cannot heat the heat exchanger.
Where does it go? Well it didn't go to the pipe nipple! Then we have convective heat or the scrubbing of the heat exchanger surface. In order to do this a certain volume of gasses have to be produced or we end up with laminar flow which means the cooler gasses travel to the outside and insulate the hotter gasses from the heating surface. The flue temperature is low because there just isn't that much heat produced. It is a lot easier to verify this on a furnace by measuring airflow and temperature rise. A little harder on a boiler unless you really can measure the GPM accurately.

The BTU's of fuel is based on stoichiometric combustion which doesn't exist in the field. An oil flame can reach about 4600 degrees while a gas flame can be 3600 degrees. The question I ask is if your flame temperature on oil is only 3900 degrees are you still producing the same usable btu's? This means even at the factory rating your input is still low. No mechanical device can be tuned by setting input and yet our industry to this day promotes input.

Those that measure output have seen the difference in btu's in versus btu's out. Underfiring lowers the percentage of btu's out assuming the equipment is tuned the best it can be in either.

Long Beach Ed

So then...

I am very open-minded to this; as it is obvious that too small a fire would affect efficiency negatively. The question is how to determine the minimum effective firing rate. How would you plot this curve?

It sounds like this would be quite difficult, if not impossible to measure in the field. It would be entirely dependent on the internal structure of the heat exchanger and fire box.

Without the ability to determine the rise in water temperature over a specific firing time, how would you know when your under-firing is being counter-productive? Why even the water flow rate through the vessel would affect this.

Some manufacturers specify this firing range. Others just give a fixed nozzle size.

Gordy

Levels of Efficiency

Interesting debate.....I think it needs to be noted that there are different levels of efficiency with in the whole heating system though.


Btu content of the fuel of choice to start. We are talking oil specifically here. But we all know that certain fuels will have varying btu content depending on blending. Except for electricity.


How efficiently the fuel is being burned hence the combustion analyzer. Like Jim says though, its kinda like a broken watch. Combustion efficiency varying with the btu content of the fuel which can change.

How efficient is the HX transfering the btus being made to the water in the HX. We all know there are alot of styles of HXs. Some are better than others at getting the most heat from the fire to the water.

Last there is the emmiter efficiency. Alot of styles, and variables there which is drifting off this topic.

I will have to say that running the highest level of fire the boiler allows sounds a bit counter intuitive to what a mod/con boiler is suppose to achieve for efficiency by modulating its firing to the load.

To me the statements are like saying that you should run the highest temperature rating of an emmiter no matter what the weather is doing outside in order to be efficient. That means that condensing /modulation, outdoor reset are smoke, and mirrors. Just my observation though.

All in all as steamhead has said there is no bandaid for improper whole system design.

My comments may be off, but I think that there is not apple to apple comparisions being discussed here. Whether it is going to save oil down firing a boiler that is twice as big as needed to do the job. Real old man sounds like you have made a few more adjustments than simply down firing your boiler, and is your boiler twice the size needed to do the job.


Gordy

Constantin

Gentlemen,

There may be a simple solution / explanation that makes both of you right. I believe Jims observations are based on oversized boilers and furnaces with very large flue passages. I could see how a lower air flow through those kinds of heat exchangers could be less turbulent, more laminar and hence even though the stack temps are lower cause less heat to be transferred to the walls (though this also suggests excess air, BTW).

On the other hand, if you have a "tight" heat exchanger, such as the many different incarnations found on the modulating gas side of the aisle, I think the equation changes dramatically. There, the gases are scrubbed pretty good, explaining why manufacturers can publish graphs that show increasing thermal and AFUE efficiency as equipment is modulating down. The reason may be the ~1mm wide passage in a Vitodens or Gianninni HX versus the 0.5-1.5" wide flue pipes found in a lot of residential furnaces, for example.

So, in my mind, Jim's observations may be correct for the kind of equipment he found in the field 30 years ago, whereas realolman has pretty good proof that downfiring worked for him with more modern equipment (i.e. a tighter boiler that still gets pretty good HX). Similarly, some manufacturers have published AFUE ratings for their equipment, showing higher AFUE's at the lowest input rating, not the highest input. Who knows, perhaps the AFUE test method skews the results, but most variables are controlled in this instance (same equipment, same conditions).

So in my mind the equation very much depends on the kind of equipment, including the HX, the controller, the method by which the fuel/air mixture is metered, etc. All of those presumably have an impact on how well a combustion appliance will function.

Weezbo

Jim do you discuss fire box configurations,

in relationship to flame pattern? ok maybe that would more easily explain what you mean by under firing...

with flow absorption patterns within boilers changing for best heat transference , i have asked many manufacturers technical staff about firing at a higher temp and flame configuration this is immediately discouraged...no further conversation available...

is this something to appease lawyers or is it due to over regulation of certifying agencies ..?

Jim Davis

Actually the combustion efficiency of most fuels is about 99.99% if our CO is less than 100ppm or are smoke is less than #1. Combustion analyzers are trying to calculate the heat transferred assuming that we are firing at the maximum input and maximum btu's of the fuel which is almost never.

Resetting water temperature or cycle time is how to adjust equipment for load conditions not firing rate. Modulation is similar to the old hot deck/cold deck rooftop equipment. It was for comfort when fuel was cheap. The old adage is that by keeping equipment running there is less wear and tear on parts. Can buy lots of parts for thousands of dollars in savings. Commercial fire-tube boilers that modulated needed partial re-tubing almost every year. When modulating was minimize this problem seem to diminish quite a bit.

I do not wish to be controversial but only write what I have experienced for the past 30 years. It just doesn't agree with what everyone has been told. Notice how few manufacturers require combustion testing or they won't give us warranty. I have seen very few that actually list a proper flue temperature when that should be one of the simplest things to know and diagnose problems. It is not much different then everyone setting gas appliances at 3-1/2" and thinking they are doing a great job. Just because that is what everyone has been taught won't ever make it right. But manufacturers in our business know that 95% of contractors don't test and that is the only safe thing they can do.

Constantin

But Jim,

Just because an appliance modulates does not mean that modulation is the cause of all boiler failures. Design failures can play just as much a part of that equation than the control / firing strategy being employed. Perhaps the "commercial fire tube" boilers you encountered were never properly designed for a modulating application.

FWIW, there are literally thousands of modulating heating appliances out there giving their owners great service at considerable fuel savings. Yes, they require more care, on average, than the equipment they replaced, but almost every manufacturer asks for yearly service... That the older equipment could survive without service doesn't make it right.

Lastly, the project I was involved with in Maine has saved the owner 46% on the LP fuel cost over the preceding year, despite the fact that the previous (oversized) 83% atmospheric system (2x Buderus 124X) was only 12% more efficient AFUE-wise than the single Vitodens that replaced it. IMO, modulation, low mass, low-temp capability, and right-sizing all contributed to the savings.

The owner is on track to make up the total investment in less than 5 years, even with annual service contracts by Viessmann-trained staff. I'd say that's a pretty good payback considering that any unscheduled increases in fuel prices will simply accelerate the payback even faster.

realolman

From my perspective

it all boils down to a simple concept: I want to get all the heat I can from a gallon of fuel when running my boiler.

Please humor me in a simple ( minded? )proposal:

I set my boiler up with a 1.1 GPH nozzle using an analyzer. I shut all the valves to the boiler with the water temp somewhere around room temperature, and the pressure well below popoff.

Then I fire the boiler for an amount of time, and check the peak water temperature.

I will then do the same proceedure for a 0.65 gph nozzle.


Can I not divide the btu s supposedly in the oil that I burned by the btu s needed to raise the temperature of the boiler water, and determine which nozzle is the most efficient in my boiler?

In my attachments, assuming 12 gal. water in the boiler, I'm coming up with .0646 gal. used by the .65 and 0.1204 gal. used by the 1.1 ...43% efficiency with a 1.1 GPH and 78% with a .65 GPH. Even if the actual percentages may not be completely correct, isn't it obvious the .65 is the one I want in my boiler?

If what I am doing is incorrect, where is it flawed?

John Abbott

down firing

You are not wrong.All of us that have been in the trade for a really long time know that down firing with a hot water boiler (not steam)will save energy if the boiler is oversized which it is 90% of the time.The laws of physics apply to all of us.The longer the burner cycle the more efficent it is.Modern burners and I am talking residential make smoke on start and stop so the longer the burn the less the smoke.We need to compare apples to apples not oranges.I suspect the same rules apply to larger burers but as I have limited experience with them (not over 1,000,000 BTU so I will refrain fom making assumtions.Oil burners run more efficently with a hot combustion chamber so the longer the cycles the better which is why the Beckett heat manager is so effective.

bill_97

I'm with ya , realolman

I have a Peerless WBV3 . It has a range from .60 gph to 1.10 . As the nozzle size increases , the AFUE goes down . Same thing for the boiler I mainly install , the Burnham V8 .

Although I don't believe AFUE is the best way to measure true efficiency it does show us lower inputs means lower consumption . But I think with each boiler there's a threshold where efficiency will drop when the nozzle size goes too low . Like burning a .75 in a 500,000 btu boiler .

By the way - 1500 sq ft home , WBV3 with an indirect and outdoor reset . Using .50 nozzle , I'm at less than 400 gallons this season . I was over 800 gallons before I used the smallest nozzle and the OR . I wish I knew which change gave me the best savings .........

Jim Davis

All the boilers I am talking about are factory spec modulation. There is a big difference between an atmospheric boiler and a low mass boiler. First there is no atmospheric than get get higher than about 71% efficiency in the real world and most are in the low 60's. We use to save 20% just switching from cast iron to copper fin. I agree the new low mass boilers are really efficient and do better on modulation because of the low mass but still lose some efficiency because of it.

Most commercial industrial boilers had full time engineers working on them so they got all the service they needed. The wear and tear was still caused by modulation because that was the only thing we changed and the maintenance dropped to minimum.

real- Based on flue temperature there could only be a 2-1/2% difference in efficiency worse case senario. Chart makes no logical sense at all? Sorry, just don't see how those numbers could be possible. Maybe the timeline and chart lines need more identification. Might be nice if you showed the O2 readings with both burners also. No matter how small the pan is on the stove, it still heats much faster with a high flame than a low one.