Near boiler piping/replacement boiler

The piping size is adequate for the load you have connected. 100' of fin tube could supply about 55,000 BTU/hr. Seems like plenty for 1800 square feet? No sense in having a boiler sized larger that the fin tube can put into the space. So a 60- 75,000 BTU/hr boiler would be adequate.

If your current boiler is twice that size, 120,000 or larger it probably short cycles and runs 70% efficiency range.

or a buffer tank. a buffer tank is probably the only thing you could do that might come close to paying for itself

A heat load would add some more info to the question. 1800 sq ft X 25 btu/ ft guesstimate= 45,000BTU/hr required. That is on the coldest day.

80% of the heating season the load could be in the 30,000 range. So the boiler 152,000 you have could be 3-4 maybe 5 times what you need.

While` not hydronically ideal for that boiler, the circs are not causing efficiency issues on the return, unless the system has noisy air issues?

Here is a simple buffer piping, direct to load method. Indirect on priority with its own circ.

@katman, The Aquastat that you have, may be the Original Equipment Manufacturer (OEM) specifically designed for WM. That control may not have the ability to operate as a WGO cold start boiler. If your system was originally installed with a WGO boiler and an indirect for DHW, then the control would automatically be set for cold start operation. All that said, since you are no longer using the Coil for DHW, there is no need to maintain any minimum temperature in the boiler when there is no call for heat of call for DHW. Set the control to the lowest temperature for LOW LIMIT as possible. If you can go as low as OFF that is the best setting for your situation. that will result in the lowest fuel usage. In the future, if you ever need to replace the Aquastat Control… Use the universal model that can be set to OFF in order to convert this WTGO to cold start operation like the WGO. Except for the tankless DHW coil, the WGO and WTGO are the same boiler in every other specification.

As far as setting up the burner to fire at 1 GPH with a .85 nozzle, that is where I would start and see if you get the minimum stack temperature of 350° within 5 minutes of cold start operation. If you do, then leave it there and look for signs of flue gas condensation on the vent connector, after several weeks of operating at this lower input. You may be in good shape.

FYI:  If you originally had a WGO boiler of the same series, the OEM control would have been the L8148 aquastat.   You would not have the option to set a low limit with that control because there is no low limit.  Weil McLain does not see that maintaining  a minimum 135° on a cold start boiler has any advantage.  Their 66 and 68 series boilers also came with the L8148 aquastats and there are many of those 35 to 50 year old cold start boilers still operating across the country. The only advantage to maintaining 135°F in your boiler is to your fuel oil supplier.  They make more $$$ the more oil you burn. 

As far as repiping the boiler so the circulator pumps are located on the supply side of the boiler would be: if you are experiencing air problems. If you constantly need to purge air from your system (more that once a year) because you have no heat in a zone or a radiator resulting from air in the system, then you will gain an advantage in that repipe job, if designed correctly. Otherwise, if it ain't broke don't fix it. Lacking any air issues, there is no fuel savings or thermal efficiency to be gained my redesigning the pipes. The only advantage is to eliminate air problems.

At the 10 minute mark, boiler at 155, baseboard at 126°. Is that the return from the baseboard? Hopefully you are not leaving the boiler at 155 arriving at the bb at 126°?

Ideally within 10 minutes or so the return at the boiler should be over the fuel dewpoint. So getting to @130°F within 10 minutes or so is ideal. Burner adjustment CO2 has some to do with dewpoint also.

If the boiler cycles off before warming above 130, you could be getting condensation in the block.2

On the indirect call, boiler hitting high limit at 6 minute tell you that you could be flowing more btu to the indirect so it can absorb full boiler output. Not a dealbreaker if you get adequate DHW and recovery time?

point the camera at the copper pipe not the aluminum fins

Or at the copper return pipe at the boiler.

Are you sure you have the right fuel selected for the analyzer.

Your efficiency numbers can’t be correct.

Looking at the 13 minute numbers here is what I might want to look into

The temperature difference (∆T) between the supply and the return water is a little high. 29°F (almost 30° ∆T) means one of two things. Either the water is staying in the radiators too long, or a new zone just opened and is sending cold water to the boiler and mixing with the hotter return water from the previously operating zone(s). You need to have a more controlled test procedure. Perhaps have all zones calling at once, then check steady state operation after 15 minutes. That will show the real operating ∆T

11.8% CO2 with a gross stack temperature of 383.6°F does not equal 92.43%. When you look on a combustion efficiency chart for #2 heating oil and you take into consideration the NET stack temperature. (383.6° minus 70° room temperature is a net of 313.6°, for example) you will get a combustion efficiency closer to 85%

Of course you may get different number if you set your electronic instrument to "LP" or "Nat" gas. Double check your settings

A thermometer with a clamp type probe will give you more accurate readings.