Oil boiler efficiency

This seems too easy....is underfiring an oil boiler gaining efficiency? Appears so, since the stack temp is lower and the ratio of boiler surface area to flame quantity is higher. A customer account I serviced about a week ago claims an engineer had him grossly underfire his 5 section Burnham V7 oil boiler, and it appears to be heating the 7000 sq. ft house just fine, and he says it only burns 800 gallons/yr, hot water included. Nozzle size was .85 gph but with 140 psi fuel pressure, so actual firing rate is 1.05 gph. Stack temp was 350F. The boiler is rated for 1.65 gph. Hmmmmm.

As far as the heat transfer efficiency between the hot combustion gasses and the metal water jacket (heat exchanger) of the boiler, a lower firing rate will increase efficiency. However the other aspect of overall system efficiency, namely combustion efficiency, may be adversely affected depending on the combustion chamber design.

The problem when you drop below 80 % of the Max firing rate is low CO2 and too low of a stack temperature. If you can produce proper numbers your fine...


Seems like someone used a rule of thumb on your job.........Best doing the math before installing the equitment

You might ask him if you can run a combustion test for him, to see what it is.

Sounds like his boiler was way over sized for his house to begin with, if its keeping his house warm at design temp.

Yes it is more efficient to underfire it as long as the chimney doesn't condense.
He will need to save his money when the boiler springs a leak.
The V7 boiler is junk and will leak right around 5-10 years. They no longer make this model.

I'm with oil lp on this one.
One way to improve efficeincy is to lower stack temp, always being concerned about excess air though, you can only go so low before the savings are lost due to improper combustion.

Lo-fire state is the most in-efficeint state to run a burner.

Time to break out the Bacharach. I'd bet dollars to donuts his CO is sky high.

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Originally posted by GradyWhite244
Time to break out the Bacharach. I'd bet dollars to donuts his CO is sky high.

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I never check Co. Only smoke readings on oil units. Its easier to get a cleaner burn with a downsized fire. Certainly easier than if it were running at maximum firing rate.
The only exception that I have seen on this is if the boiler is a Buderus. And especially if it is a Riello burner. These units I would run with only one size nozzle. That is the size that is required by Buderus. They run better with a positive over fire draft. If you downsize, they will get a smoky or oily flame.
Doesn't matter what kind of crappy chimney you have. These units compensates for that.

After testing equipment in the field for 27 years, whether it was industrial, commercial or residential, underfiring equipment has led to higher fuel bills 100% of the time. Every heat exchanger has a certain mass to heat. The radiant heat of the flame and the scubbing of the flue gases cannot be accomplished without maximum input. A combustion analyzer will always calculate a higher efficiency when down firing is performed, but it is 1005 misleading. Had a oil furnace once that was too big for a house but when it was fired at 1.25gph instead 2.00gph it used 600 gallons more oil than it had used in 15 years.
Not measuring CO on oil can subject the customer to an unsafe condition. Oil burners can make thousands of PPM of CO at Zero Smoke!

I've done what you said you've never seen.
With becketts, and carlins.
Not just take out an old burner and put in the carlin, or beckett, but on units that came with those burners.

But, you can't go over board and do 35% down fires or you will use more fuel.

When i worked for oil companies we tracked the results for 3 years, and it should that those customers were indeed saving on fuel.

When i use to p/m boilers i found that i could underfire about 10% and increase the pump pressure from 100# to as much as 140# too increase fuel(#2)atomization to give you better combustion effiencys. A given example is a new burnham boiler with a 78% effiency rating would change to a 81 or higher % effiency. Our job was never complete in less you had a your effiency analysis setup report completed. This effiency increase did not apply to all boilers/burners. Another old trick was on late night or call outs with nuisance lockouts due to poor/intermitted flame signals and charcoaled blast tubes was to paint it after cleaning it with silver metalic paint and get your ass home. My soot sucking days still live on from 12 yrs ago...........

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Originally posted by gasnowman
. Another old trick was on late night or call outs with nuisance lockouts due to poor/intermitted flame signals and charcoaled blast tubes was to paint it after cleaning it with silver metalic paint and get your ass home.

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LOL... Your either showing your age, or you worked with simulair old timers like i did.

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Originally posted by beenthere
I've done what you said you've never seen.
With becketts, and carlins.
Not just take out an old burner and put in the carlin, or beckett, but on units that came with those burners.

But, you can't go over board and do 35% down fires or you will use more fuel.

When i worked for oil companies we tracked the results for 3 years, and it should that those customers were indeed saving on fuel.

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You saw a savings because of a better burner and possibly set-up. But take all those systems now and bring them up to their mechanical ability(not just the rating plate numbers)and additional savings would be attained each and every time if the O2 or CO2, smoke and CO were the same. Flue temperature will be slightly higher when greater inputs are used but then it should be known that the greater the temperature difference the greater the rate of transfer.