gas fired boiler help

Discussion in 'Boiler Forum' started by recon, Sep 18, 2011.

  1. recon

    recon New Member

    Messages:
    2
    Location:
    Rhode Island
    About 4 yrs ago my wife & I put in a new Weil-Mclain oil fired boiler, now with oil almost $4 a gallon. I'm thinking of switching over to natural gas. I have a question for the experts.

    What is the best quality gas fired boiler to get???
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,183
    Location:
    New England
    The first critical thing is getting one the proper size. The tendency for ages has been to do a rough calculation (or just look at what was there) and replace it with one the same or larger - this is rarely the proper solution. Any boiler will only reach its efficiency specs steady state...each time it starts then shuts off, it wastes some energy and it takes awhile to get up to max efficiency, if it ever does. Short cycles are death to a combustion device and a hit to your wallet as well.

    There are a bunch of decent boilers out there, but one critical thing is to find one that is well supported by parts and technical expertise. Any boiler needs to be installed and set up properly, or it will not meet your expectations. All that being said, when I looked around to replace mine a few years ago, I called a bunch of contractors, got a bunch of opinions, then decided on a Buderus unit. The US factory/distributor is about 15-miles from my house, which didn't hurt, either (in Londonderry, NH).
  3. Tom Sawyer

    Tom Sawyer In the Trades

    Messages:
    3,236
    Location:
    Maine
    changing to natural gas will not save you a dime.
  4. Dana

    Dana In the trades

    Messages:
    2,933
    Location:
    01609
    At $3/gallon (lower than currrent pricing) and 85% combustion efficiency you're getting ~40KBTU per dollar into the heating system. At $1.50/therm (higher than current pricing) and 80% combustion efficiency you'd be getting ~53KBU/$. That's about 30% more heat per dollar. At the actual New England fuel prices it's even better. If you then consider that the boiler is likely to be at least 2x oversized, and could easily be 3x or more it's real AFUE will be 75%, and replacing it with a modulating condensing boiler you'd be getting 90% real AFUE your heating cost would be less than half at current prices. But mod-con boilers are expensive, and your existing boiler has decades of life left.

    Installing a retrofit gas burner makes more financial sense than simply scrapping what's practically a brand-new boiler. If it's oversized for the load (far more likely that not, in RI) integrating a smart-economizer such as the Intellicon 3250 HW+ or similar onto dumb aquastat control will usually bring the efficiency closer to it's rated AFUE. Properly adjusted you should be able hit 80% or better with a retrofit burner. Depending on the type & quantity of radiation you may be able to use an outdoor reset type controller and do about as well. All told the retrofit w/smart controls would likely come in under $3K, whereas a new right-sized cast iron boiler would likley be north of $5K and run about as efficiently as the retrofit solution. A high-efficiency modulating-condensing unit could easily run twice that. It could take decades to pay off the difference between a simple gas conversion burner and a mod con on fuel savings, and in most cased investing the difference into air-sealing & insulation on the house would likely pay off sooner.
  5. recon

    recon New Member

    Messages:
    2
    Location:
    Rhode Island
    Guys,
    No company in this area will retrofit my existing boiler to a gas unit. They will only replace whole unit with a new one. I know I tried I called dozens of heating companies.
  6. Dana

    Dana In the trades

    Messages:
    2,933
    Location:
    01609
    That's surprising to me, since just a few 10s of miles up the Blackstone from you in Worcester gas burner retrofits are pretty common. (There was a real run on them during the 2008 oil price spike. My next-door neighbors retrofitted their nearly-new ca. 2003 Burnham oil fired steam unit with a gas burner at that time, and had the oil tank removed, cutting their heating costs in half. It paid for itself in 2 heating seasons.)

    To make a realistic assessment of what makes sense we'd need to know what the 97.5th or 99th percentile out door temp heat load is. Short of doing a lengthy heat loss analysis, if we had a zip code and your fuel use correlated to specific calendar dates, and the model/size of the oil boiler it's easy to put an accurate upper bound on the heat load. The size of the heat load, and the type/amount of radiator/baseboard you have may dictate the boiler choices. Even a single annual fuel use number and the boiler specs can get pretty close. If your oil vendor includes a "K-factor" on their billing (as many do), that helps too.

    Also, do you heat your hot water with the boiler? If yes, is it with an indirect tank, or with an embedded coil inside the boiler?

    Steam, or hydronic (pumped hot water)?

    Radiators, or baseboard?

    There may be sensible alternatives that also make more economic sense, such as putting an Intellicon economizer control on the existing boiler along with installing a high-efficiency mini-split heat pump to carry some or most of the heating load. At 15 cents/kwh electricity a mini-split would deliver ~57KBTU/$ of heat to the house, compared to an ideally-sized 85% oil boiler giving you only 39.1KBTU/$ with $3/oil, or 33.5KBTU/$ with $3.50 oil. Even if the mini-split didn't carry the whole load at +5F (which is about your 99% design condition in RI), the boiler can. But if most of the time most of the load is handled by the heat pump, your oil use would be cut by 80-90%.

    An 83% mid-efficiency gas-burner would deliver 66.4KBTU/$ at $1.25/therm gas (55.3KBTU/$ @ $1.50/therm gas) but would cost somewhat more than a 2-ton mini-split, and wouldn't provide air-conditioning. A modulating condensing gas-burner might deliver 76KBTU/$ (with $1.25 gas) but would cost north of $10K up front, taking a good long while to pay off the difference on fuel savings alone.

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