Changing input firing rate without changing orifice size

Ted89

I have a 2014 Trio P3/Carlin EZ NGas boiler. With the welded flange (not universal) version and factory drilled .189” orifice it should fire at 85k BTU/hr. At installation it only clocked at 76k. DHW production via an indirect tank was marginal so I asked them if they could get it up to spec. They made a change and it actually went down to 68k. They did not change the orifice (I was there). What could they have changed to make it drop? What can be done to increase it?
Thanks very much

JUGHNE

If the orifice is fixed then the only other adjustment is the gas pressure, IMO.

Jamie Hall

And furthermore... whoever is doing the fiddling with that thing needs to check the entire gas train and air, and adjust the whole show with the proper instruments. You have enough trouble with that puppy.

Don't even try to do it by eye or by ear.

EBEBRATT-Ed

The Carlins I have done all came with the orifice drilled to the smallest size. We then drilled it in the field for the input we needed. Don't know if all their burners come that way. Drilling the orifice doesn't make a perfect machined smooth hole, I am not surprised your 9000 btu/hour off. The lab is the lab and the field is the field. This is nothing new

I would tweak the pressure slightly to get what you need. As others have mentioned combustion testing is a must.

As far as dhw production their are many thing other than burner input that can affect that. Temperature of boiler water, size of circulator and piping, domestic cold water temperature and draw.

HVACNUT

What's the lockup pressure? What's the pressure with other appliances on?
I'm almost positive manifold should be 3.5" w.c. so if it's under that, incoming pressure is too low or the adjustment on the gas valve is off.
You've had numerous posts concerning issues with your boiler. Like @Jamie Hall said, someone is fiddling by T&E. Not the best way to work on a gas burner (or any potentially dangerous application).You need a qualified tech, and you still haven't posted any combustion readings, so I'm curious if it was ever done. It leads the way to tell the tech what's going on with combustion. If draft, CO2, O2, CO (typically <50 ppm), stack temp are within manufacturer's specs, there shouldn't be a problem.
A fouled flame sensor doesn't cause soot. It has no effect on BTU's.

Ted89

Thanks for comments. Some of you are aware of a more complex problem I’m having, but for this thread I was hoping to just understand the single issue of “can the firing rate on this burner be changed without changing the orifice size.”

But let me answer your questions:
1. The installation and all servicing was by the same company and a master gas technician using a combustion analyzer. All 6 combustion performance figures. All changes were then checked with it. Not by eye and ear. I have changed nothing.
2. According to Carlin, my new burner had the .189” orifice factory drilled. I will verify it is still .189”. Spec input for that size is 85k BTU/hr.- I get 68k per the meter.
3. At last servicing, the technician was looking carefully at the lockup pressure reading- he didn’t tell me the reading but acted like it was a bit unexpected. Will inquire. I don’t understand the significance on fire rate.
4. DHW: the Tekmar control, its settings, the flue & chimney setup, the dedicated indirect Boilermate tank/piping run/010 circulator was left as is when changing to this boiler in 2014. The firing rate of the old boiler was also about 85k. Regardless, it’s not relevant as the DHW perceived downgrade just got me to think that getting back closer to the 85k input spec was worth doing. I still do.

A new question: One of you said changing the ”gas pressure” can affect the input rate. Seems obvious but I have been told on HeatingHelp that changing the gas valve output manifold flow pressure (now 3.5”) can’t change the fire rate. Am confused. Can it?

You have all been very generous with your time helping me understand more gas heating basics before I go back to my service company for more checks on the bigger problem. Thank you. But on this thread I am just trying to understand how someone can change the fire rate without changing the orifice. If changing the downstream valve flow pressure doesn’t affect it, the only thing I can think of is the 30’ ½” connection tubing from the meter could be insufficient. FYI, static supply input to gas valve is 7”. Can’t find my table. No other NG appliance in the house.

Thanks all!

JUGHNE

How about a picture of the boiler, including the burner, regulator and gas lines?

And is the gas tubing yellow or black CSST?

captainco

According to a standard gas orifice chart a .189 orifice is 90,695 if the btus in the gas are around 1030 per cu.ft. at 3.5" W.C. If you are only getting 68 cu.ft. of gas then the orifice is not the size stated or marked. I have seen orifices stamped with one size but the hole was a different size. This might have been the last one drilled with a worn drill bit?

1/2" of gas pressure changes the volume about 6% above 3.5". Below 3.5" it can change up to 7%. You just happen to have a natural gas water heater. How would one check the same problem on LP with no meter to clock? Combustion testing is the best way to set it up but one has to know what numbers to look for and I have not seen too many manufacturer that provide that information, especially flue temperature.

Tim McElwain

Just to answer your question about input. With a fixed orifice changing the gas pressure higher or lower will definitely affect input. As I suggested earlier I would have some one start from scratch and check everything and then do a combustion analysis.

Tim McElwain

The Carlin burner because of how the orifice is located in a fixed manner inside the pipe it can sometimes instead of being a drilled round hole it is oval shaped due to poor drilling. This will cause sooting many times.

Ted89

Thanks for reply.
I assumed the Carlin factory can drill a proper hole. They said they drilled it to 189". Was that a bad assumption? I will verify it.

Ted89

Yellow tubing.

JUGHNE

With all other parameters being equal, 1/2" iron pipe could pass 52,000 btuh and 1/2" Tracepipe claims 55,000.

These numbers are from the simple charts.
I have found it easier to just up the pipe sizes rather than crunch more numbers trying to make it work.

There probably is a utility company regulator just outside at the meter. Often these are considered infallible and ignored.
The gas valve would be the second regulator.
Both should be checked during operation.

captainco

The simplest method to determine if the piping is small is to check gas pressure at the inlet of the valve when it is closed and then when it is open. If the gas pressure drops more than 1" you have a supply problem.

HVACNUT

@Ted89. With multiple threads of basically the same issue, i.e. flame loss within a minute or two, flame impingement, orifice size and gas pressures.
I can't understand why your tech can't tackle this.
A qualified tech should have been able to address everything, from diagnostics, tests, repair, replace part(s) if needed, adjustments, combustion test, done.
What's all the hubbub, bub?

Jamie Hall

I'm not sure he's got a tech, @HVACNUT -- but he sure has a messed up boiler and burner...

Tim McElwain

Ted89
A new question: One of you said changing the ”gas pressure” can affect the input rate. Seems obvious but I have been told on HeatingHelp that changing the gas valve output manifold flow pressure (now 3.5”) can’t change the fire rate. Am confused. Can it?

That is incorrect! If I change the gas pressure at the outlet by changing the setting on the gas valve regulator from 3.5" W.C. to 3.6" W.C. then the firing rate would increase. If however I reduced the outlet gas pressure to 3.4" W.C. then the firing rate would decrease.

Tim McElwain

A new question: One of you said changing the ”gas pressure” can affect the input rate. Seems obvious but I have been told on HeatingHelp that changing the gas valve output manifold flow pressure (now 3.5”) can’t change the fire rate. Am confused. Can it?

That is incorrect! If I change the gas pressure at the outlet by changing the setting on the gas valve regulator from 3.5" W.C. to 3.6" W.C. then the firing rate would increase. If however I reduced the outlet gas pressure to 3.4" W.C. then the firing rate would decrease.

Tim McElwain

If my calculator is correct a .189 orifice is the same as a # 12 drill size or 3/16. If so at 3.5" W.C. with btu content of gas at 1050 and specific gravity at .6 it should be firing at 110,000 BTU's unless I am missing something?????

Table 1 in the Carlin manual says 3/16 on natural gas should be 75,000 BTU's I guess compensating for the air band opening and increased pressure. The notes say "maximum burner input decreases with increasing overfire pressure. Assume a reduction in maximum burner input of approximately 5% at at.1" W.C. and 10% at .2" W.C. This has to be taken into consideration.

So at 5% it would be a reduction of 5,500 from 110,000 or 104,500. At 10% it would be 11,000 reduction from 110,000 or 99,000. If memory serves me the other posting about this job says you wanted 85,000 BTU's.

EBEBRATT-Ed

@Tim McElwain

Overfire pressure reduces the gas input.

On commercial stuff I use a manometer and connect the left side of the manometer to the gas manifold and the right side of the manometer to the combustion chamber. Then whatever the furnace pressure is pushes back on the manometer and you set the gas pressure to 3.5" above furnace pressure.Most commercial pressureized boiler now have a 1/8 or 1/4" pipe tapping to the combustion chamber. don't know about residential stuff

Tim McElwain

@EBRATT-ed

That also works on residential power burners in fact sometimes you may get different readings depending on where you locate the overfire test probe. It should be above the burner.