Outrageous draft readings
I work for a school that has 2 zf 600-ls unilux boilers. Nat gas. Powerflame burners cr4 burners. So I just started working on these a few months ago since the guy retired that used to. The buildings a complete disaster but what I noticed when both boilers were idle yesterday, some serious whistling from the combustion air dampers on both boilers when off and at min damper position which is like a 1/4 inch gap. For the heck of it I tested draft with both boilers off for the day cause it was warm out, I have .18 to .24 draft with boilers off. So today I checked with a boiler running, they switch boilers every cycle. One fires, then once that one reaches sp it shuts off, then the other one fires next time. They short cycle like crazy in warmer days,like 4 min runtime,but when firing the draft gets up to .3" which seems insane to me. There is no draft regulators, I would think there should be a dual action reg on each boiler. You can literally hear the heat being sucked out of them after shutdown. Then one just starts back up 2 min after the other shuts down. Loses psi fast. Set at 5psi because of hx's. I've already replaced some very old Webster 0026t's that were probly original to this building and I have many more traps to replace, e.o.m. and individual convector traps so hopefully that will allow system to not lose pressure so fast. But jeez. What have I gotten into here guys? Lol the venting of the 2 boilers is, the boiler on the right comes up with just a 90 into the common, then about 10 feet where the left boiler tees into it then another 6 ft to the left 90s into stack. All metalbestus
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Not farmalier with the boiler is it forced draft pressure fired or neg draft.
What kind of chimney or stack are they connected to?
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Four minutes enough to let everything stabilize!
our boilers changed once a week. Number one lead number two lag number three standby. Next week number two lead number three leg number one standby.
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That boiler looks like forced draft.
Your best bet would be to call Unilux for recommendations.
They might recommend barometric dampers or sequence draft controls (which you don't want) they are big $$$$$$
I will take a wild guess that these boilers replaced old boilers that needed a huge chimney and natural draft.
Sounds like you have more chimney than you need.
Some forced draft boilers like a Smith 28 or Weil McLain 88 have a manual adjustable damper at the flue outlet.
Are your boilers equipped with those?
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If you are anywhere in Pennsylvania or an adjacent state call 410-821-8900 and ask for the service department, They may be able to help.
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There's no fd fans or Id fans. Just a gas powerburner and yes the chimney is massive. At some point about 25ft of height was added to it, not sure if that was for these boilers when installed in 2007 or the previous boilers. I am going to contact unilux I've read the iom for these and doesn't talk about draft. Just was trying to see what you guys thought about the -.3" draft. Thanks
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Chimney has a 36" round tile flue. I think it's tile anyway. We'll over 100 ft tall, too tall to measure ill have to try and find the prints from when it was extended. No manual dampers. Over 6,000,000 input each so not sure if sizing is correct,havnt looked into it that far yet but I think I will now.
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From your description of the chimney, it probably was for coal boilers from many years ago. Those things were massive and when they got warm produced a tremendous amount of draft. I saw a lot of those in Pennsylvania. They were a thing of beauty. Any boiler hooked to that type chimney always needed an automatic boiler outlet draft control system to control the draft. From looking at that boiler on the Unilux web site it looks to be a typical 3 pass fire tube boiler with nothing special. I would have to see the job but it probably should have draft controls and not just a manual outlet damper.
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I understand exactly what you're saying about the old coal fired boilers, but this stack was built in 1952 for 2 much smaller btu boilers than exists now, that were oil fired. 20k edr. I have the original prints for the building I've been looking at. Actual blue prints. So cool. So much easier to read. The original boilers had no brand name, they were built custom out of fire brick,iron,insulation and decorative brick on the outside. Not much detail on them other than that unfortunately. At some point they added height to the stack for the replacements. At least 25 ft if not more,I think more. I can't get up that high to measure without a lift. I'm trying to find the reason why the stack was extended and at what point in time. Nobody knows but the town hall should have these records. I have the combustion analysis records of when these boilers were installed in 2007 but wouldn't you know they list everything but the draft. Lol. Wonder why. They were oil fired only when installed in 07,then in 2018 they were told by a contractor cleaning it that they arnt designed for oil and they need to get gas only burners installed. Which is bs. I think they just got sick of cleaning so much soot every year. These boilers are very hard to clean. You need rigging gear to break the panels down for access to tubes. But anyway, I want to do everything I can to at least try to make this situation better so I called unilux today but they had me send an email to one of their guys with my situation. I'll post back when I hear back. Thanks for taking the time and interest with this
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That chimney is massive and is causing your draft issues.
Not an easy fix and will be $$$$
As @retiredguy mentioned sequence draft controls will be expensive.
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You should rarely have to clean out soot from a boiler just because they were firing fuel oil. If that is the case you need to switch your service company to a better more knowledgeable company. Some boilers will soot a small amount and if that boiler can and does have nat gas connected, switching to nat gas for a couple weeks should burn off the soot if the combustion is set properly. I know that this works on most installations since I did it many times. Can you post a picture or 2 of this boiler so we can get a look at it. I hope for your sake that this boiler is not one of those 5 pass tube boilers that were made in the early 2000's. They were a pain in the a** to work on and clean. If those boilers are those, they only trick is to set the combustion slightly lean to stop the burner from making soot. This does not always work.
Sometimes, height was added to a stack in an attempt to get the combustion products higher into the atmosphere to alleviate peoples complaints about odors from the boiler's exhaust. This rarely worked to solve that problem. Also, if there is an obstruction such as a hillside or higher building near that stack it can cause stack problems and even the occasional down daft.
By the way, where in the USA are you located? There a lot of reputable companies that use this site that you could call for help.
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I had wondered if it was extended in the era of get the stack up higher so the pollution is higher in the atmosphere to get rid of local pollution. Especially if there was also an incinerator connected to it.
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