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Boiler producing excessive soot


Neal Lewis
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Here is a pic of a gas boiler that is only a couple of years old. This thing must have been producing soot from day one. The burner flames were solid orange and rolling out the front. The system was obviously not professionally installed. The adjacent boiler was clean as a whistle, but was half the BTU's. I know there might be a combination of reasons, but is this caused by insufficient gas pressure?

BTW, there was heavy soot deposits in the first floor apartment.The boiler was running continuously and didn't respond to the thermostat. The apartment temp was regulated by opening the windows. The occupant had suffered from a stroke more recently.

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I would guess insufficient oxygen for proper combustion and improper venting of the exhaust.

"The occupant had suffered from a stroke"

Uh-oh. I've read many articles that state chronic CO poisoning is frequently misdiagnosed as, among other ailments, a stroke. Carbon monoxide displaces oxygen in the blood.

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Guys,

The boilers are in a wide open basement; no problem with combustion air. The draft hood spill switch did not shut the boiler down. There was an opening into the base of the chimney which showed that the flue was clear at the bottom. The adjacent water heater and boiler did not have any drafting problems or soot buildup.

I believe that the section passages are now blocked with soot, causing the extreme flame rollout, but something was causing the excessive soot production to begin with.

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Originally posted by Neal Lewis

Guys,

The boilers are in a wide open basement; no problem with combustion air. The draft hood spill switch did not shut the boiler down. There was an opening into the base of the chimney which showed that the flue was clear at the bottom. The adjacent water heater and boiler did not have any drafting problems or soot buildup.

I believe that the section passages are now blocked with soot, causing the extreme flame rollout, but something was causing the excessive soot production to begin with.

Neal,

You may be right, but just because the basement was wide open, doesn't mean they had enough air.

Consider this:

A single boiler with a 100,000 btu input needs 625 square feet of basement (assuming an 8' ceiling which would be high in my area). Two boilers that size would need 1250 square feet. Add in a couple of water heaters and you can see that most basements aren't big enough to supply them all with enough combustion and dilution air. If you there is a clothes dryer (which draws air from the basement and vents it outside), and it's not hard to starve a boiler for air.

Anyway, you noticed the problem and no doubt told your client to have it checked out by a heating expert. Job well done.

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If it was starving for air, wouldn't that cause a small flame, do you think it would cause soot?

If the air mix was out of adjustment, at the burners... couldn't that cause a poor flame and sooting? (lazy yellow)

It the flue was blocked or was not getting proper draft, couldn't that cause a poor flame, sooting and roll back?

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Just food for thought... If it's a particularly long and oversized masonry flue the gases could be cooling and becoming heavy before exiting. This can cause all the same problems as a blocked or restricted flue. A draft inducing fan may be necessary.

Also, old brick masonry flues usually were separated by simply a brick shiner stacked up the chimney, which I've never understood. It's a really bad idea because eventually they tend to fall into the flue to one side or the other blocking the flue.

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Originally posted by StevenT

If it was starving for air, wouldn't that cause a small flame, do you think it would cause soot?

If the air mix was out of adjustment, at the burners... couldn't that cause a poor flame and sooting? (lazy yellow)

It the flue was blocked or was not getting proper draft, couldn't that cause a poor flame, sooting and roll back?

Yes, lack of combustion air will cause sooting. As will the other conditions you mentioned.

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My first guess is blocked jacket. This would cause that amount of soot very quickly. Also the flame shield is not burned away and does not look warped, so the temp never was getting too high. All soot is air/gas mix and if the sections were obstructed at all, they would build soot. Jim brings up a good point re: combustion air. Most inspectors do not think this through and assume a large basement will have lots of free air.

Pull the jacket and clean it up and set burners - betcha' it will be fine.

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"Roll out" like that when adequate combustion air is available can only mean one thing, an obstruction.

The obsruction could have started anywhere in the exhaust system but will eventually plug everything up all the way back to the burners.

The amazing thing here is that you didn't mention anybody being killed by the fumes.

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George wrote:

The amazing thing here is that you didn't mention anybody being killed by the fumes.
Yeah, but the occupants probably have very pink complexions and the neighbors have probably been shaking their heads for months and saying something like, "Poor ____ and _____. They've always been such nice folks. Have you noticed how red their faces are lately? They must be hitting the bottle pretty regularly these days. What a shame!"

OT - OF!!!

M.

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  • 3 weeks later...

icon_speech_ugh.gif[:-crazy] This is why any gas or oil appliance should be setup using an electronic co/combustion meter and a draft gage.

Another possible cause for the sooting is no bypass loop on the boiler. Newer boilers have less mass and less water. If the boiler is installed on a system with cast iron radiators a lot of cold water will be returning to the boiler. A bypass loop allows a small portion of the heated water to mix with the return water and bring the temperature up and reduce condensing and sooting.

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