Stack draft question

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I am very familiar with woodstove temperaments as far as stack draft and it works by limiting the intake but in some situations the draft is too much and has to be modified to get the efficiency out of a stove. I have a gut feeling that the draft is too much with my new boiler set up. Beckett burner. With oil heat can you limit the draft or is this out of the question because of carbon monoxide. This is a clay lined chimney 27 feet tall.

STEVEusaPA

What is the make/model of the new boiler and burner? It's possible with a 27' chimney and no draft regulator that you draft is too high.
Yes you can limit the draft, but specifically you have to adjust the draft to the manufacturer's specifications. Some newer boilers require 0 at the breach and up to +.02 over the fire...so proper draft is the first step to better efficiency.
As long as its drafting properly, installed properly, adjusted properly and working properly, CO won't be an issue.

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Steve, It's a Purepro Trio P3 with a Beckett AFG burner. Thanks for the insight. My previous house I built I went with a Buderus and learned that system. Very efficient radiant with curtainwall panel construction over timberframe. Just moved to a home in VT with cracked boiler and could not seem to get the required (by me) 3 bids to make a decision for a new install. So I went ahead and stapled up 1200 ft of Onyx then my buddy said to read Pumping Away. Next thing I knew I was ordering a boiler, a bunch of pipe, circulators...Well, no leaks and she fired right up. I like learning. Anyway, I distinctly remember opening my Buderus little flap to look at the flame. Wow the heat was incredible. I also observed the flame. On this Trio boiler, not nearly as hot and the flame was noticeably different. Correct nozzle, correct nozzle to end of gun measurement. What tipped me off is that I could adjust the air intake with little noticeable difference. On the Buderus, all that it took were minor air adjustments and huge differences in the flame occurred.
With all this said, this heating install have been a fun adventure, now I just have to make it as efficient as possible.

Jamie Hall

On a 27 foot chimney I would expect to have two dampers on the breeching. The first, quite close to the outlet from the boiler, is in the breeching itself and is adjusted when you adjust the overfire draught and air for the burner, which you need to do with instruments to get the correct air to fuel ratio and the correct overfire draught. You can't do it by eye. The other is a barometric damper (so called) which is on a T on the breeching. It's function is to open when the stack draught is excessive to additional air in, and it is fully automatic, controlled by counterweights on the damper blade. It keeps variations in stack draught from affecting the overfire draught of the boiler.

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Jamie, the first damper you mention, what does it look like, specifically called and how does it work? Where I have gotten so far is I purchased a Testo 310, bought a T barometfic damper, and at the breech achieved the correct stack draught. With that my combustion gasses came in line and have 86 % efficiency. But to get there, the T is wide open. I was curious about this other damper but am unfamiliar with it.

OuterCapeOilguy

I would never consider installing an oil burner without installing a barometric draft regulator. Without it, you can't possibly get a steady co2 percentage or stable flue gas temperature. The results will vary from heat wasted up the chimney to excessive sooting of the heat exchange surfaces (and carbon monoxide production). Most equipment manufactures stress installing a regulator, and adjusting it for -0.02" water column. This must be done BEFORE any other tests or adjustments.

STEVEusaPA

What was your draft at the breech?
Your boiler with that burner is looking for +.02 over the fire and -.02 to -.04 at the breech. Which to me is a little odd in that if I had +.02 OF and -.04 or even -.02 at the breech I would assume the boiler needs to be cleaned or had some other problem.

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Hi Steve, right now I am in Saudi Arabia : (, and before I left my install, I adjusted the breech to exactly what the label said on the boiler, then did a smoke test which came out clean and the Testo came out within parameters and achieved above efficency stated. Boiler has been running for the last 2 weeks with my girlfriend at the helm with no (bolier) problems. (We have a Co2 detector that is very sensitive) Just want to mention that the previous boiler had no barometric regulator! Their draft readings were -.08 and achieved 77% efficiency. These were professionals who installed and maintained the boiler. Me, being a jamoke who knows squat about boilers, ended up installing his own (piping/boiler/radiant) out of necessity but I knew instinctively, once I looked at the flame, something was wrong with the draft. Then I bought the barometric draft, the Testo and the smoke tester so I could be self sufficient. What I haven't done admittedly yet is do an overfire reading which I will do as soon as I get home. But my question is, since right now my regulator is wide open, what if my over fire reading can not be achieved within parameters? Do technicians ever put in a damper before the barometric regulator?

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FYI this forum made install much easier.

Jamie Hall

A damper before the draught regulator (barometric on a T) is very common indeed. Goes in line with the stack, and has a calibration plate on the outside so you can easily see where the blade is.

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Thank you Jamie!