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2 stage gas valve retrofit and boiler de-rating results

mikeg2015mikeg2015 Posts: 760Member
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.


  • mikeg2015mikeg2015 Posts: 760Member
    Logically, if the sections so need cleaning, and I transfer more heat, that will reduce the draft rate, reduce excess air draw, increase resonance time, which should further reduce stack temp.

    The efficiency numbers are estimated from a chart and CO2 is calculated in the meter. Meter only measures O2 and temp with a manual pump bulb. CO was measured separately with another meter. Measurements taken just inside the collector before the draft hood as far as I could insert the short tube without getting burnt. Might get better numbers if removed the cover and drilled a hole in the collector.
  • Inliner311Inliner311 Posts: 25Member
    edited March 4
    Thanks for putting this up. Did you change to an intermittent pilot to use the Honeywell two stage valve?

    I want a similar long term setup like you. I think my boiler is better size than your current one. I want to add TRVs. I've actually been buying up Honeywell Evohome parts so I can have a smart trv system with the ability to call for heat by each zone and not having a main thermostat. It's also why I want a two stage gas valve so I'm not short cycling if only a handful of zones are calling for heat.
  • mikeg2015mikeg2015 Posts: 760Member
    I already had intermittent ignition and a flue damper.

    I as thinking this morning that when I resize the boiler I could use a remote bulb on a “control” radiator and sense when it’s fully heated to drop to low fire. I might put TRVs on everything except that one. and at that point I could go to a vacuum system.
  • FredFred Posts: 7,813Member
    edited March 4
    mikeg2015 said:

    I already had intermittent ignition and a flue damper.

    I as thinking this morning that when I resize the boiler I could use a remote bulb on a “control” radiator and sense when it’s fully heated to drop to low fire. I might put TRVs on everything except that one. and at that point I could go to a vacuum system.

    I would think putting TRV's on all radiators has the potential to make the boiler way oversized, almost all the time, even on low fire. What's your goal? It would also seem to me that you are looking for an alternative to a Vaporstat to switch from low to high fire. I'm not sure one radiator, fully filled, is an option. What would be the relationship of that radiator to all the others on the system or the room temperatures? I would think your goal should be to down fire at some pressure before full radiator(s) to keep the system pressure from building before full radiators. Using a "typical" radiator at an equal distance and vent rate to all the others might be geri-rigged to work as an on/off switch but with all the variables I doubt it will work system-wide.

    You're going to end up with a one-off system that no one will understand or be able to work on if you are no longer around. It's hard enough to get good steam people now, creating a Frankenstein system will likely result in one of two fixes:

    - Being called a knucklehead and returning the system back to a vanilla steam system or
    - Attempting to fix what is there and screwing it up even more.

    Experimenting and finding new ways to do something is great but adding a lot of complexity and maybe losing some of the system benefits, not so much. JMHO
  • EBEBRATT-EdEBEBRATT-Ed Posts: 5,618Member

    with a heat loss of 110K adding the pick up factor and 20% for boiler efficiency you 175K sound like that what you need.

    But with the current boiler is 375k input and your new low fire is 70% of that or 262K input

    Why run on low fire at all.
  • Inliner311Inliner311 Posts: 25Member
    I personally appreciate the innovation. After researching TRVs, there just isn't enough info out there for one pipe systems. I do agree that you should try to keep in mind that your setup should be easily turn back to a basic system. I would personally go to a smaller boiler that is the proper size for your full system minus any TRVs before adding all the TRVs to the system. I wouldn't trust that anyone can sort thru TRVs with lack of info out there.

    Keep the old parts just in case you decide to move and you can put the system to the most basic system possible. Keep all the old vents so you can remove the TRVs, maybe even label all of them so you don't have to rebalance the system. Keep the single stage gas valve and pressuretrol.

    Lastly keep us posted on what you are doing and how it's working. I think the more info out there with more people trying TRVs and two stage gas valves, the less daunting it will be.
  • mikeg2015mikeg2015 Posts: 760Member
    No good way to use a vaporstat. My system never builds any measurable pressure.

    I’m seeing the flaw in using too many TRV’s. I considered that. Will probably just use the vaporstat to downfire on the future boiler but start with a small boiler to begin with. TRV’s only on upstairs and eliminate upstairs from calling. Might go back to a seperate thermostat for it. Doesn’t integrate with my heat pump as well as I want because it causes the blower to run at heating fan speed since it’s a communicating thermostat. The minimum I can set it to run is almost as high as cooling airflow.

    I agree that I need to keep in simple. Few steam boilers left around here. I only know of 3 myself. One home recently burnt down.
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