Boiler question ?

Discussion in 'Boiler Forum' started by Dario, Mar 2, 2021.

  1. Dario

    Dario New Member

    Joined:
    Mar 2, 2021
    Location:
    Croydon pa
    What is the best gas cast iron hot water boiler with no domestic coil And going to use a chimmy with a liner installed. I have weil mclien oil cast iron now going to rip out this summer.thanks
     
  2. Sylvan

    Sylvan Still learning

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    Sep 23, 2004
    Occupation:
    plumbing - fire suppression - boiler inspector
    Location:
    New York
    Weil-McLain , Burham, HB Smith, Dunkirk boilers
     
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  4. Dana

    Dana In the trades

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    Location:
    01609
    The best cast iron boiler would be the one sized with output no more than 1.4x the 99% heat load (per ASHRAE), with some system design to prevent return water from being cool enough to condense inside the boiler.

    Most existing oil-fired boilers are ridiculously oversized for the space heating load, usually 3x or more if it has a tankless coil. Don't simply replace a 120KBTU/hr out oil-burner with a comparably sized gas burner, only to serve a 35-50K space heating load. Do some analysis first.

    Start with a fuel-use based heat load calc to ballpark the design load needs with reasonable accuracy. With this type of load measurement the distribution & standby losses are already included (they can't be isolated out), so you'd be looking at the DOE output numbers on the boiler, not the IBR/Net-Water output numbers.

    Then measure up the radiation, to see if an appropriately sized boiler would be at risk of condensing. A typical 3-plate cast iron boiler delivers about 50-55,000 BTU/hr (DOE), which would be about right for a house with a 35-40,000 BTU/hr heat load. But with a boiler that size if there is more than 150 feet of fin-tube baseboard the return water temps would be on the edge of condensing, but (usually) easily fixed by some near-boiler plumbing tweaks. The cool return water condensing problem becomes even more important to address if the system has a lot of high-volume cast iron radiators, but it still doesn't make sense to oversize the boiler to fix it, just be aware of the issue going in and design for it.

    For the record, what's the gph on the nozzle of your current oil burner (or the nameplate DOE-out number, if you're not sure how the burner is jetted.)
     
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  5. fitter30

    fitter30 Well-Known Member

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    Feb 2, 2020
    Occupation:
    Retired service tech
    Location:
    Peace valley missouri
    Nozzle gpm are rated at 100 lb pressure. Some techs and manufacturers use a higher pressure which raises the gpm rating. Some techs write the nozzle size on front of boiler. No 2 oil 140k btu's per gallon.
     
  6. Dario

    Dario New Member

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    Mar 2, 2021
    Location:
    Croydon pa
    0.70gpm on burner D.o.e rating htg. Cap.water,btu 86.000. Water btu hr 75,000 weil mclain p-wgo-2
     
  7. Dana

    Dana In the trades

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    Jan 14, 2009
    Location:
    01609
    Either the Weil McLain CGa-4 or Burnham ES2-4 would likely be an easy direct replacement for your WGO-2, but it's probably not the right boiler for your loads. The smarter controls on the Burnham ES2 would deliver higher as-used efficiency than the W-M CGa if your 99% design heating load is smaller than 60,000 BTU/hr. (Most homes in PA have heat loads lower than that, with the exception of uninsulated solid brick or stone houses.) There are others.

    At 0.70 gph the oil burner is near the low limit of what works with the #2 fuel available in the US, and even at that smallest size is often/usually still sub-optimally oversized for typical home heating loads. With a calculated heat load it should be possible to down-size to something more appropriately sized for the actual load. Run the fuel-use heat load calculation. If you are on a regular fill-up service that stamps a "K-factor" on the billing slips a few wintertime K-factors and your ZIP code (for design temperature estimation purposes) would be enough.

    With a real heat load number it's likely that you would get higher comfort and efficiency with a cast iron boiler smaller (maybe even much smaller) than the existing oil burner. Also, it's often even cheaper and more comfortable to install an ~80- 100 KBTU/hr condensing gas boiler than swapping in another oversized cast iron beast, and either mothball the chimney or use it as a chase for the inexpensive plastic venting used by condensing equipment.
     
  8. Dario

    Dario New Member

    Joined:
    Mar 2, 2021
    Location:
    Croydon pa
    A little bit more info on my home 1 floor ranch 1,675.00 sq ft 150 ft of fin tube argo baseboard. All new windows in house house is well insulated Chimney will just need a good stainless steel insulated liner for future for boiler . You guys are spot on my wgo oil now is way oversized. And boiler only runs in the winter for heat house has a gas water heater 40 gal bradford white . both water heater and oil boiler are 22 years old .thank you
     
    Last edited: Mar 4, 2021
  9. Dana

    Dana In the trades

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    Jan 14, 2009
    Location:
    01609
    Stainless steel liners are quite expensive compared to the plastic venting used by condensing equipment.

    If the 150' of baseboard is all one zone you have PLENTY of baseboard for running a condensing boiler. Even at low condensing temps sufficient for low to mid-90s efficiency (~125F out, 115F return) that's enough baseboard to emit ~30,000 BTU/hr (~200BTU/hr per running foot), which is probably more than the load at your 99% outside design temp (about +17F in the Philly area- yes I know it gets a lot colder than that.)

    A tight well insulated house that size with l0w-E windows is likely to have a design load of only ~20-22,000 BTU/hr, and wouldn't need a boiler with more than ~30,000 BTU/hr to be able cover even polar vortex disturbance cold-snaps. The smallest commonly used cast iron boilers are probably still too big- the W-M CGa-25 has a DOE output of 44K (~2x the likely load), the Burnham 202e is good for 32,000 BTU/hr, which would be better (if your actual load is that low, which is why you should run a fuel-use load calc.)

    Given the 150' of baseboard with a cast iron boiler you'd need to oversize it or design in a boiler bypass for a right-sized boiler. Without well designed & implemented bypass plumbing need something like 50K+ of DOE output to avoid chronic destructive condensation inside the boiler, which is getting into ridiculous-oversizing territory (which is at least better than LUDICROUS oversizing! :) )

    An 80,000 BTU/hr modulating condensing boiler with a 10:1 turn down is probably the best bet, something like a Navien NHB-80, or an HTP UFT-080W, (either of which can modulate down to ~7500 BTU/hr) or even a combi-boiler that can throttle back to the <22,000 BTU/hr range if a tankless water heater is appealing to you as a replacement for the B-W. There are others, but either of those two are likely to have a lower installed cost than a mid-efficiency cast-iron boiler with a new stainless flue liner.
     
  10. Dario

    Dario New Member

    Joined:
    Mar 2, 2021
    Location:
    Croydon pa
    If i go with the cga25 do i need a insulated chimney liner or no ? I would like to stay with weil mc
     
  11. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609
    Read the manual. I believe you can use B-vent (double-walled galvanized) venting- it need not be insulated.

    Pay special attention to section 3 starting on p.22. That much baseboard on a burner that size needs to treated somewhat as a low-temp system, with local bypass loop to protect the boiler.
     
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