High CO at 3.5inwc gas pressure

Ldallas_87

From what I have been seeing on this forum, 3.5 wc gas pressure is common for atmospheric natural gas steam boilers. My dad has an Enerjet boiler from the late 80’s and unfortunately it has no specifications on gas pressure. 

At 3.25 wc the boiler was producing around 400ppm at the flue. When I brought it down to 2.85, it’s at a much better 50ppm. Has anyone seen something like this? 

Jamie Hall

Do you have any way to adjust the draught or the air? High CO is usually a symptom of inadequate air.

Ldallas_87

The only thing I can do is add an intake fan to the vent which has a direct path outside. However it does bring in a good draft and the testo measured ambient oxygen at 21%. 

ch4man

clean the scale out of the fire side of the chambers

Ldallas_87

Thank you for that suggestion. I will definitely do that. 

EBEBRATT-Ed

What are you measuring the gas pressure with? Gauges and testers can lie to you.

A water tube manometer never lies.

How are the O2/Co2 when you are at 2.85"?

Jamie Hall

Have you actually measured the draught? And is that the only fresh air source for the room in which this unit is placed? If so, unless it's a very small burner, you don't have enough combustion air.

Ldallas_87

I used a digital manometer from Amazon and I probably should have went the old fashioned way. I have not measure the draught. And yes that is the main fresh air source but there are rooms on either side of the boiler room and windows can be cracked from both sides to supplement the vent. I did multiple readings (O2 was approx 5.5, CO2 approx 8.5%

Ldallas_87

I should say that the boiler seems to be oversized. It takes about 3-3 1/2 minutes to cycle between .5-1.5 psi when I timed it today at “2.85” wc. At “3.5” inwc it would cycle too fast, approx 1:30 seconds between cut in and cut out 

mattmia2

Jamie Hall said:

Have you actually measured the draught? And is that the only fresh air source for the room in which this unit is placed? If so, unless it's a very small burner, you don't have enough combustion air.

I looks like there is a water heater in there too.

The cycling on pressure is a separate issue to address after you get the combustion right. You need o look at the edr of the boiler and the connected radiation and also make sure the air can get out so the steam can get to that connected radiation.

Ldallas_87

Fireside doesn’t look too bad although I will still try to get in there with a brush. 

Jamie Hall

As firesides go that looks pretty decent. I really think your problem is not enough combustion air -- but i would add that it really doesn't do to try to adjust a gas burner (never mind oil) without the proper measuring equipment... and certainly not down firing (which you have effectively done by changing the pressure) without a full combustion analysis.

Ldallas_87

Okay thank you. I will get a professional to check up on this. 

captainco

When there is a combustion air problem the CO will continue to rise indefinitely. Combustion air problems cause low draft. Low draft causes CO2 to back up and block O2 to the burners. Watch the numbers and see if they remain the same after 3 to 5 minutes. If the CO and O2 are stable, then your problem is not combustion air. If they are changing, then the draft must be measured to determine if it is a combustion air problem.

One exception to the low draft combustion air problem would be a flue restriction problem, which can also be diagnosed with a draft gauge.

Ldallas_87

The co, co2 and 02 remained stable. I was able to measure draught using the Testo 310 and it fluctuated from -.1 (.980 pa) to -.2(1.96pa) mmwc. However it occasionally went down to 0. Temperature hovering at 394 F.  There was no option for a lower pressure measurement on it. Outside temp was 56 degrees. The fluctuation of pressure was concerning and I noticed that my dad has no chimney cap. I wonder if the wind is affecting draft. Is that possible? I opened the basement door, put a fan by the door blowing into the boiler room and didn’t notice a change in pressure. 

My thinking is that as Jamie Hall mentioned there is not enough air to supply the boiler at full 3.5” gas pressure and if I were to bring the pressure up to that amount whilst adding a intake fan to the boiler room, in combination with a chimney cap to reduce backdrafts,  draft pressure will go up. 

Also excess air was measured at 32%  and I saw in a video that closer to 50% excess is ideal. 

captainco

You are measuring combustion in the wrong location. If CO is 400 ppm there it is going to be a lot higher below the drafthood where it is not diluted. Also, wet flues in mild weather causes draft to be low. Definitely need a rain cap. Wind does affect most rain caps. Field Controls makes a Star Kap that minimizes wind affect!
Please drill a test port below the drafthood. You might find the numbers there less stable. This could be very dangerous!!

Ldallas_87

Just for clarification, I measured draft above the draft hood and combustion below it. Also, I got CO to 50 ppm (70-75 u CO) but only after bringing gas pressure to 2.85 inwc.  Thank you for the chimney cap recommendation. 

Zman

Yes, ^^^^ measure the exhaust before it is diluted. One easy way to determine if you are lacking CA is to open the doors and windows to the space. If the numbers change, you have a CA issue.

captainco

You can open doors and windows, but just on days the wind isn't blowing or it will be misleading.

retiredguy

If you can determine that the amount of combustion air in the boiler room is OK then you have to look for another culprit. This may be way off base but you could have worn gas orfices. I would clock the gas meter to get a good idea of the gas input and see if it higher than the rating of the boiler. If it is, then a new set of orfices would be necessary.

pedmec

clean your burner tubes and retest. dust on the burner tubes will affect how well your gas/air mixes on an atmospheric boiler. are your co2 and o2 readings @3.5 wc or 2.85 wc. you should run @ 3.5 wc. your excess air is fine. you don't want too much excess air as all it does is remove heat from the boiler.

wmgeorge

It could be very well that the system was designed to run at the pressure he has the lowest CO. Also assuming he has adjusted the burner air shutters. Also as I recall a combustion analyzer measures CO as one of the test points.

captainco

It may not look like much dirt but with those small of passages it can be a good restriction. O2 below 6% is okay if the CO is below 100 ppm.

wmgeorge

That fresh air intake, boiler and WH have been in that same room for what, 50 years? So what has changed, gas pressure or combustion air adjustment, dirty burners?

pedmec

i haven't seen an atmospheric boiler designed run at anything but 3.5 wc. not much engineering with an atmospheric boiler after going to market. while i agree with you the manufacturer can spec what they want, its industry standard to use 3.5wc on atmospheric boilers. and very rarely to you see burners with shudders, unless its a hydrotherm multitemp (unless someone has seen other brands). you'll get different pressure settings based on the type of burner your using. multi-stage boilers have different pressure ratings for different stages.
the problem with a lower gas pressure is you take the chance of ignition in the burner tubes if its not designed for the lower pressure. utica boilers use to do that all the time. sounds like a jet airplane taking off.
as i said before. clean the burner tubes and then test. you don't test an air conditioning system with a dirty condenser. why would you do a combustion test with dirty burners.

captainco

Anytime you start to clean a piece of equipment, furnace or A/C and don't check how it is operating before you touch it, then you can be blamed for anything that is wrong with it when you do turn it on. Test in and test out are critical! A company I worked for many years ago, gave away a lot of free service because they were blamed for the equipment not operating after they cleaned it.

SlamDunk

In pharma, we document "as found"; "as left" data for all of our calibrations. I do it on combustion burners too; it's the only proof you have to say you left it 'as found' or better. Tuning a burner is nothing less than a calibration.

That is good advise @captainco. Even though it is a memory muscle for me, I don't think I have read it on this site before.

Ldallas_87

Thanks for all the great input. The burners were cleaned before I did any testing and unfortunately they don’t have any shutters.  The boiler and WH have been there for at least 40 years. Yes the 02 and co2 numbers posted above were at 2.85 inwc. I wish that my dad kept all the labels from the boiler but unfortunately they’re gone and I have nothing to go on. I’m happy the CO is at a good level at that gas pressure and it still heats up the home fast. I will look more into intake air and draft. 

captainco

It is a shame that everyone thinks if equipment is set at 3.5" it has to be safe, Over and over we have found burner orifices that were miss stamped, drilled incorrectly or someone tried cleaning them with a drill bit. I am pretty sure no one checks each and every orifice to see if it is the correct size. The area opening of an orifice can change at least 1000 btus if the orifice area is .00018" bigger or smaller. Not sure who carries tools to measure this. Any equipment that is set by checking gas pressure only is a possible incident. Still believing that a blue flame is safe is one of the biggest lies in our industry!!

EBEBRATT-Ed

@Ldallas_87

I wouldn't dwell on it. If it runs ok at 2.85 leave it alone as long as it heats the house

wmgeorge

EBEBRATT-Ed said:

@Ldallas_87

I wouldn't dwell on it. If it runs ok at 2.85 leave it alone as long as it heats the house

Agree, just because you as a serviceman, have never seen it does not make it wrong. No air adjustment then its the gas pressure. Same room same boiler for 40 years, same fresh air intake.

mattmia2

captainco said:

It is a shame that everyone thinks if equipment is set at 3.5" it has to be safe, Over and over we have found burner orifices that were miss stamped, drilled incorrectly or someone tried cleaning them with a drill bit. I am pretty sure no one checks each and every orifice to see if it is the correct size. The area opening of an orifice can change at least 1000 btus if the orifice area is .00018" bigger or smaller. Not sure who carries tools to measure this. Any equipment that is set by checking gas pressure only is a possible incident. Still believing that a blue flame is safe is one of the biggest lies in our industry!!

Stepped plug gauges or plug gauges is how you would measure directly. If it is out of round that won't be accurate and it will get you within a thousandth or so even if it is pretty true but somewhere around 5000 btu is probably where it starts to matter. A rig to measure pressure and flow is probably more accurate for this application.

Steamhead

Clocking the meter is a good starting point.