How rich is too rich

Driven11 · 2:40AM

Battling the HTP phoenix lite that I've named "tuba". Foghorns like a sonofa for the first 30 seconds or so after ignition. I tried all the usual suggestions and the only thing that works is throttling a little rich. It's out of spec though. Manual calls for 8-10% for low and high fire. I keep low around 8.5 for some excess air to keep the burner cool but high is closer to 11 if I want silence. Maybe a little more. CO stays well under 60 so I don't know if I should even care as it's more efficient combustion the higher that CO2 goes. I've searched and searched and nobody ever has a real answer to all the modcons that howl besides richen it up.

mattmia2 · 2:47AM

co of 60ppm seems kinda high, you are probably on the low excess air side of the curve.

Mad Dog_2 · 8:04AM

I'm not sure where you operate out of, but in New York, the Natural Gas Utilities want CO flue #s under 50 PPM as a rule. Mad Dog

HVACNUT · 11:36AM

Each manufacturer has their own specs on CO in the flue. Most want <100 ppm CO. Some like the NTI Trinity allow up to 175 ppm CO in the flue. Not saying its right, but…

Jamie Hall · 1:42PM

You probably aren't confused, but I've seen it enough times to feel a need for a caution: CO and CO2 are not the same thing. And in combustion work in general, CO will increase with a richer mixture, while CO2 will increase with a leaner mixture.

Another sort of useless general comment: sometimes you can get a resonant sound — like a tuba maybe! — from unstable combustion, but other times you can get a similar sort of sound by simply varying the air flow — and it may change as less air or more flows through. This can be altered by draught, for instance. Or of course any air shutters.

Ironman · 2:02PM

Is any portion of the gas line CSST?

EdTheHeaterMan · 2:24PM

Screenshot 2026-06-11 at 10.22.31 AM.png

This is certainly not Too Rich

Driven11 · 2:24PM

https://forum.heatinghelp.com/discussion/comment/1898308#Comment_1898308

Only the 6" piece HTP uses inside their control panel. Completely hard piped.

Driven11 · 2:27PM

I agree but also hear comments like "anything below 100 is fine". What else can I do besides have the noise? And why does it only happen for that short time at ignition? You'll find 100s of these type of threads with a quick Google search but none of them ever seem to have a detailed, proven explanation. Some say pipe, some say vent, some say regulator, but when those items are changed it never seems to solve anything.

mattmia2 · 2:29PM

there are 2 places where you can get the same CO2 value. you are on the left side, you want to be on the right side.

Driven11 · 3:03PM

https://forum.heatinghelp.com/discussion/comment/1898314#Comment_1898314

Yes I'm on the right side 100%. I thought of that. The readings verify based on my gas adjustments. I'm between 3 and 4% O2 currently.

Jamie Hall · 3:06PM

Just a thought — but have you tried going way lean? Just enough fuel in the air to fire up? and then adjusting back richer? Until the CO2 peaks and the CO maybe beings to show an increase?