Convert steam radiators from oil to gas

Discussion in 'HVAC Heating & Cooling' started by netmouse, May 7, 2013.

  1. netmouse

    netmouse New Member

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    84
    Location:
    NJ
    With winter over, I am back thinking about conversion from an oil burner/boiler to natural gas. I have a very old 2-story Victorian house with steam radiators.

    I ran into someone I know who did this a few years ago. He also is the plumber on a local team that provides this service as a business. He also has steam radiators like me in an old 2 story house, and said he installed a furnace that has 90+ efficiency with a pipe out the wall (not chimney). This surprised me as I have been told for steam radiators you need to use an oil (gas) burner, not furnace. I asked what brand, he believes it is American Standard.

    What is going on - can a more efficient gas furnace (not burner) be installed? I'd been hearing about burners for steam radiators that have about 83% efficiency.
  2. Dana

    Dana In the trades

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    For the heat distribution via steam radiators you need a steam boiler (which is not technically a furnace.)

    The high boiler temperatures required to make 215F+ steam result in higher stack temperatures (= a greater fraction of the heat going up the flue, which means a lower raw combustion efficiency), so you'll never hit 90%. But 82-83% is do-able with natural gas (you can do slightly higher combustion efficiency with oil, maybe 85-86%, but that's it), and that's where the better steam boilers live these days when new, with both the boiler & system dialed-in.

    To hit 90% the exhaust temp has to be WAY under 200F, which takes return water from radiation to be under 125F. That simply isn't possible with 150-200F water returning to the boiler from the radiators. There is no such thing as a "condensing steam boiler", except those where the cool makeup water is being pre-heated by a secondary condensing economizer. SFAIK those systems that exist are limited to commercial boilers, not residential systems, and even with those hitting the 90% number requires some system design optimization. It's conceivable that your friend has a system large enough to handle the output of a smaller commercial steam boiler with a condensing economizer for preheating the make-up water, but it would be unusual for residential systems.

    It's possible to retrofit an oil-fired steam boiler with a gas "conversion burner" at a reasonable price tag. If it's a decent oil boiler you'd be able to hit ~78-80% efficiency with a gas conversion burner, but if it's an ancient asbestos covered pig that had been converted from coal to oil you'd be lucky to hit 70%, and it's worth considering an all-new boiler.

    American Standard steam boilers have been around for a long time, but I'm not sure they're still making steam boilers under that name. The Burnham Independence series seems to be a popular replacement boiler in my area, and can hit 83% when tuned. The Weil-McLain EG series is pretty similar and also hits the 83% range when dialed in. I'm sure there are others.

    The high temperatures and large surface area of steam piping also requires a decent R-value on all steam piping (including the return plumbing) in order to hit a reasonable system efficiency. Retrofitting 1" wall-thickness ~R4 fiberglass or rock wool pipe insulation not cheap, but if the boiler room is the warmest place in the house during the winter a large fraction of the heat is being wasted, and even at buck-a-therm gas there is real payback on it. The goods sold at box stores is usually 1/2" wall thickness or ~R2. It's worth going online or to a real plumbing supply distributor to get the 1" or thicker stuff, which won't be much more expensive than box-store pricing on the thin stuff. If you can't find it locally, try these guys.
  3. LamdaPro200

    LamdaPro200 In the Trades

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    Sounds like he converted from steam to hot waters with a 90% boiler not a furnace. Have you looked at the Burnham MegaSteam. It is a 3-Pass Oil Fired Steam boiler with an AFUE of 86%. You can't get a cast iron gas boiler close to it even on the hot water side.

    http://www.usboiler.net/products/boilers/megasteam/

    Here lies the problem when converting an oil boiler to gas via a conversion burner such as a Midco Economite. You have voided any remainder warranty you have on the existing boiler and have essentially turned it into a non rated, non UL listed appliance. I'd check with my homeowners insurance and make sure that god forbid you converted it and it was the cause of a fire or other accident because it now is installed outside the boiler manufacturers installation manual and ratings and most likely would not be covered. Can it be done. Yes and there are many out there. Just do your do diligence before hand.
  4. Dana

    Dana In the trades

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    Most insurance carriers won't void anything as long as the local inspectors signed off on the retrofit conversion burner installation. If the boiler is more than 10 years old, the value of any remaining warranty isn't even worth considering. If the boiler is over 25 years old it's probably worth a full replacement. But if you're already on the gas-grid, buying another oil-boiler would be a poor investment.

    Replacing it with a higher efficiency oil boiler would be an expensive upgrade with very little return compared to replacing it with an 83% AFUE gas boiler. Sure, there's a 3% difference on nameplate efficiency, but it's more than a 2x source-fuel-energy price in most local markets. Oil as home heating fuel has no future, no matter how many North Dakota type basins get developed. There is no sign that increasing world oil production can really stay ahead of increasing world demand for oil as transportation fuel- the price of heating oil will continue to be volatile, with a higher than historical average price. Natural gas prices will of course rise above their current historical low, but the technology for turning the tap higher (and quickly) has already been developed, and the ability for gas production to keep pace with increasing domestic demand is clear (at least for the next couple of decades.) The proximity to regional shale gas will dampen gas prices in NJ for at least the anticipated lifespan of a new boiler.

    Conversion to a pumped hot water system is not cheap. In many cases in NJ it would be cheaper to implement 2-3 heads of ductless air source heat pump (as both high efficiency heating + air conditioning) as it would to convert most steam systems to a condensing gas hot water system, and the operating costs would be comparable. A wet-head heating plumber might do the conversion on his own home, but for someone to pay him at full rate to convert from steam to hot water could be daunting, usually uneconomic compared to a conversion burner or slipping in a brand new gas-fired steam boiler.

    Even after switching fuels (whether retrofit burner or new gas-fired steam boiler), in an old 2-story Victorian it's probably more cost effective to spend the conversion-to hot water money on a serious round of air-sealing and insulation retrofit, which is likely to reap better returns than the efficiency jump from 80% steam to 90% condensing gas, and it'll buy more comfort too. Most homes of that era have NO foundation insulation with HUGE air leakage at the foundation sill and numerous thermal-bypass air leakage channels in the framing. A blower door test with infra-red imaging can identify where further treatment is needed, and air sealing is by far the cheapest most cost effective efficiency upgrades most homes can buy. A 2-story with an unsealed uninsulated basement has high stack effect drives, and getting that under control is job-1, sealing both the basement and the attic floor. In homes with reasonable insulation levels in the above-grade walls an uninsulated foundation can easily account for 25% of the total heat loss, from combined infiltration and conducted thermal loss from the above-grade portion of the walls. NJ used to have pretty good subsidies for weatherization efforts, probably still does.

    In short, changing to gas-fired steam and knocking 25-35% off the heat load with more serious weatherization efforts is probably going to be the most cost effective way to knock ~2/3 off your heating bill.
  5. BadgerBoilerMN

    BadgerBoilerMN Master Hot Water Mpls,MN

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    303
    Location:
    Minneapolis
    Dana has it right. Though we often see 50% reductions when replacing non-condensing boilers with properly sized and installed condensing boilers with cast iron radiators. When converting steam to hot water, higher ROI should be nearly automatic. All condensing boilers now have outdoor reset, so comfort is assured and lower fuel bill guaranteed.

    Tightening up is good but never buy new windows expecting an ROI.
  6. Dana

    Dana In the trades

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    Any quotes I've seen to date in my area for changing from steam to condensing HW using the same radiation have been way beyond any reasonable ROI (let alone a higher ROI), though probably better than replacement windows. I suppose it really depends on the system. But changing from steam to (gag, koff) hot water baseboards or other low-cost heat emitters and scrapping the antique radiators may have decent ROI with a condensing boiler, even at the currently very low price of natural gas, but maybe not.

    But that's an order of magnitude up-charge compared to a conversion burner, that would cut the cost in half with effectively NO changes to the system, and you'd buy more comfort in the meantime spending the money on envelope changes rather than highest efficiency mechanicals. When the boiler has finally had it's day, THEN it's time to think about whether or not it's worth changing up the systems entirely. Most NJ locations have see fewer than 4900 heating degree days (about half the HDD of Duluth, MN), and the payoff for the highest-possible efficiency systems is comparatively longer than in cooler climates, and maybe never at current natural gas prices. The arguments to switch over from oil to gas are more compelling.
  7. netmouse

    netmouse New Member

    Messages:
    84
    Location:
    NJ
    This is a great thread and I appreciate everyone's input. I did use the NJ rebate program to insulate attic floor and basement. 5 years ago I put in energy stars windows. And the fed credit paid much of a new huge wood stove. I am down maybe a tank of oil a year, from 4 or 5 tanks to 3.5 maybe? Still, I pay about $2800 a year for oil. I pay a bit more using a full service company that is dependable with emergency off hours number for no heat calls and do have steam specialists. If I can save maybe $1000 changing to natural gas, the payback would be 8 to 10 years depending on the conversion costs. I've interviewed several contractors (some large local companies, some independent referred by others). I just now need to evaluate the info to understand who can do the job right, as that seems what really counts, more than boiler brand. I know I am "stuck" with a low efficiency gas boiler (82%) a bit less efficient than my oil boiler (84%) or new oil boiler (86%), but I hear what you all say above. It is hard, I am a senior on a fixed income and this technology is all new to me so judging contractors is hard.
  8. Dana

    Dana In the trades

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    " If I can save maybe $1000 changing to natural gas, the payback would be 8 to 10 years depending on the conversion costs."

    Changing from (assuming the high-side) $4/gallon oil to buck-a-therm gas with a conversion burner tweaked to ~80% combustion efficiency would be more than $1500/year savings.

    $4 oil in an 84% burner:

    138,000 BTU/gallon x 0.84 = 115,920 BTU/gallon of 220F steam for $4. $4 x (1,000,000/115,920)= $34.50/MMBTU

    $1/therm gas in an 80% burner:

    100,000BTU/therm x 0.80 = 80,000 BTU of 220F steam for $1. $1 x ( 1,000,000/80,000)= $12.50/MMBTU

    The ~$2800s of oil could be replaced by [($12.50/$34.50) x $2800=] $1014 worth of gas, a savings of $1786.

    Fitting a conversion burner is usually under $3K in my neighborhood, less, sometimes zero if subsidized by the gas company (which happens.) YMMV. That would pay back in under two years.

    Even if they took you for $5K the payback is 3 years, not 8-10.

    A new boiler as opposed to a conversion burner would give you marginally bigger savings, but would take much longer to pay off, but a simple swap out for an 82% efficiency steam boiler would save you about the same money, but is likely to come in at $8-10K, simple payback in maybe 6 years. Unless your existing steam boiler is the asbestos-flaking formerly coal-fired beast that was new when the house was built it's probably better financially to go with a retrofit burner, not a new boiler.

    With any steam system it's worth recommissioning the system vents & radiator vents every 5-10 years, swapping out the corroding sticking ones for fresher versions. Using adjustable thermostatic vents on at least some of the rooms also lets you micro-zone the place for better comfort and marginally lower fuel use too. Replacing sticky or stuck radiator vents is a fairly straightforward DIY job.
  9. netmouse

    netmouse New Member

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    84
    Location:
    NJ
    Good info for a newbie to digest. I have currently an oil boiler Weil-McLain Gold Series 3 Model P-SGO-4. I understand this is a 450 sq ft, which is much larger than the EDR's I'm now being told is right. It is 14 years old, someone said too old really for just a burner replacement, go for boiler/burner replacement. Not sure cost of just a burner in NJ.

    I've done my homework and am trying to learn. I am attaching a chart of radiator measurements and also Vendor boiler choice with sq ft based on their quick EDRs.

    I am dependent on contractors. Does one, for new steam boilers and today's technology, go with a boiler just above or just below their EDR and adjust from there (up to 10% I hear)?

    My EDR using the below radiator measurements is 291 using a chart from this forum, if I am doing it right.

    Attached Files:

    Last edited: Sep 24, 2013
  10. Dana

    Dana In the trades

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    14 years old is not ancient for a steam boiler. Unless the thing has been abused somehow you should have decades of life left in it. (I've seen crummier units than that would qualify for Social Security still delivering 75% efficiency with a conversion burner.) The thing was rated 84% AFUE fired with oil, and would likely deliver ~80% with a gas conversion burner.

    It' less problematic to oversize a steam boiler to the radiation than under-sizing it, and even oversizing it by quite a bit doesn't affect system efficiency too much. The 4-plate SGO is good for ~144,000BTU/hr output fired with oil, and as long as the system has been working fine over it's first 14 years of life, sizing the conversion burner to something like 140,000-150,000 BTU/hr of output is the right thing to do.

    Checking your math on the radiation is appropriate for new boilers. If the current boiler truly is 50% oversized for the radiation you can probably drop back. Assuming your 291' EDR is correct, Burnham PIN5PV would probably be a better choice than the undersized IN-4 you have listed.
  11. netmouse

    netmouse New Member

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    84
    Location:
    NJ
    Thank you! Very helpful. And the link to Colombia Heating - that is the chart I got here to use for my EDR calc.
  12. Tom Sawyer

    Tom Sawyer In the Trades

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    Undersizing a steam conversion can be a disaster. Many of the new, smaller volume boilers will make steam very fast. So fast that the water level in the boiler drops enough to trigger the auto-feed if equipped which adds water to the system which as the cycle continues will eventually overfill the system. If the boiler doesn't have an auto fill the burner will cycle on and off rapidly.
  13. netmouse

    netmouse New Member

    Messages:
    84
    Location:
    NJ
    That is what makes this so difficult a choice for someone like me non-technical. Each vendor differs. So your input is very valuable. I'm hearing it is better to err on the high side rather than on the low side, with the EDR as the guide. And nozzles can be adjust a bit (10%) to accomodate.

    What are the specific contract facts you think are important? Someone said get in writing that all radiators will be hot within some time frame (not sure how fast, assume evenly). Also that the near boiler piping is per the manufacturer's specifications (given that newer boilers differ) as some contractors take short cuts. And make sure piping is steel, not copper.

    Anything else?
  14. netmouse

    netmouse New Member

    Messages:
    84
    Location:
    NJ
    Also, if the EDR is about the same, does it matter if a boiler has 3 or 4 sections (Peerless has 3, Utica and Burnham have 4).
  15. Dana

    Dana In the trades

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    Continuous standing pilots on water heaters (or any other equipment) don't meet US federal regs anymore. The ignition cycle on water heaters typically light a pilot with the spark, which must be "proven" with a flame sensor before the main gas valve opens up.

    The number of sections doesn't matter- different boilers have different section sizes. It's the BTU output/EDR numbers that matter, whether it's delivering that heat with 2 big heat exchanger plates or 27 really tiny ones.
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