Background - 375k BTU input HB Smith G300 circa 1983. Current installed EDR 640. TRVs installed on 160. Heat loss of the home @ -10F (design 3F) estimated @ 110k BTU. 3” header 95% insulated. System runs at <0.5oz. Vaporstat cuts out at 7-10oz indicated (lowest I could set it)
1) Previously plugged 2 of 10 burners. Regulator set to 3.5”. Still have whistling and hissing of vents on hot starts. On longer run it cuts out on pressure.
2) Installed Honeywell VR8345Q4563 2 stage valve (3.5/1.7 nominal ~70% lo fire rate). Adjusted air shutters until CO level started to rise above 20ppm. Best numbers were 12.0% O2, 5.0%CO2, 24ppm CO, 420F net stack temp on lo fire. 72% effeciency. ON hi fire, 24ppm, 11.0%, 5.5%, 26ppm, 450F. 72.5% eff.
3) Re-installed #1 & #10 orifices, adjusted gas pressure to 3.0”/1.6”. CO went above 100 ppm high on hi fire so opened shutters are little more. Lo fire 11% O2, 5.5% CO2, 30ppm CO, 400F. 74%. Hi fire 8.5% O2, 7.0% CO2, 60ppm CO, 470F stack. 75.25%
Hi stage controlled by 130F/115F snap disc clamped to the end of the header just before the main vents. I haven’t decided if I’ll leave it there. Might more it to the main header just above the boiler.
Next step - 1) remove clean outs (risk of bolts shearing so will wait until warm weather) and inspect and clean sections. Check for leaks. 2) replace leaking tube on
So CO is a little hi, but not terrible. I might mess with it a little more after I inspect and clean the sections. I need to repair some cement that’s come apart at the back of the fire box as well. That’s likely increasing me free air a little bit. Need to make sure the base is sealed as well.
I’m seeing about a 1% drop in combustion efficiency from hi to lo fire. But the longer run time and less overshoot and quieter vents make it work it in my mind. I should have tested it at full fire as a control. I suspect efficiency jumps to 76%. Dirty sections and secondary air leaks are probably driving to poor efficiency it since it’s high stack temps I’m seeing.
Current boiler rating - 340/245 Input, 255/181 Output. That’s 567 EDR on lo fire with 1.33 pickup.
No balancing issues even when I was running @ 165BTU output (517EDR) and with TRV’s open or closed. Using a mix of MoM #4 and Ventrites. Main vented with 2x Gorton #1, 1x Gorton #2, 1x Big Mouth, 3 varivents, 2 Gorton C’s. 3 vents are located at about the 30’, 60’ and 80’ points on an approx. 100’ header.
Long term I think a 175k input boiler with the 2 stage valve will be the ticket. Ill put TRV’s on all radiators except the one controlling the thermostat downstairs and upstairs. (Either can call in parallel).
Will be interesting to play with it some more and see what impact each adjustment has.