What exactly is a "trace" of smoke?

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JohnCT

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Beckett recommends first setting the air shutter for a trace of smoke (after verifying or setting the draft) but not zero smoke before testing for baseline CO2 or O2. On a typical Bacharach spot smoke tester, would that be a"2", "1" or somewhere between a "1" and the zero dot?

I mean, a trace of smoke by eye might be a 3 or 4.

71SErV8dX7L._SX466_.jpg


Thanks.

John
 

JohnCT

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Since there's no call for heat yet, the boiler won't run for more than 4-5 minutes from a cold shutdown ambient temperature to set-point high limit even with a 0.85gph nozzle, so it's hard to get a handle on the readings. The factory recommended starting point was air band 0, shutter at 3. I eyeballed the flame and settled on 2 on the shutter.

In the meantime, I was able to get two readings from one cold start run between minute 3 and 5:

First reading was about 12.5% CO2 at a smoke reading of 2-3 on the Bacharach scale with the air band at 0 and the shutter at 2. I moved the shutter from 2 to 2.5 to add a bit more air, and the second reading yielded 10% CO2 and zero smoke - so it looks like I overshot my target. That's with just a half number jump on the scale. I would have loved to dial it back by a 1/4 notch, but the boiler was at high limit and shut off so I couldn't do any further testing.

By eye there's no visible difference in the flame between the original starting point of 2 and the second setting of 2.5 (on a scale of 0-10), so there's no way these can be eyeballed.

Yes, I'm aware that the difference in readings might have been at least partially the result of short run time, so I'll wait until the weather turns colder and the burner is running for about 15 minutes or so.

John
 

JohnCT

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I received an email from Beckett tech support (quickly!) and they said a "trace" of smoke is "1" on the 0-9 dot scale. But... on the installation instructions of my old Thermodynamics boiler I found a chart that shows a trace is about halfway between 1 and 0.

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Looking at the graph, it seems that there might be less than a quarter percent difference in baseline CO2 between a smoke level of 1 and a smoke level of 0.5, so it wouldn't seem that critical if the "trace" level is a 1 or a 0.5 on the scale. I set the air shutter for a smoke reading of about a 1 or a bit less, then dropped the CO2 by between 1.5% to 2% (smoke now zero) and will call it done until late fall when the colder weather hits and the house is shut up tight when I'll retest or reset it.

John
 
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Hey, wait a minute.

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