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Thread: Advice on converting oil boiler to gas, adding indirect water heater

  1. #1
    DIY Junior Member embepe's Avatar
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    Default Advice on converting oil boiler to gas, adding indirect water heater

    Greetings all,

    I am new to this forum, looks like a wealth of info.

    General question - any opinions on this approach to improve enviro-friendliness and energy efficiency of boiler and water heater?
    -- Convert our 10 year old Smith 8 Series boiler from oil to gas; measuring at 83% efficiency (When new, rating was 86%) By conversion, I mean literally keeping the boiler but changing the fuel mechanism. We are told this is possible with this model, but don't know if it would be more effective long-term to replace the boiler altogether. Wish we never used oil, but we did.
    -- Replace 9 year old traditional gas water heater with an indirect-fired SuperStor Ultra (45), connected to boiler
    -- Include a hydrostat / outdoor reset control to modulate water temps with outdoor temps
    -- A few details: We have hot water, radiator heat, which we love. Fairly low energy use, heat partly with a wood-burning insert with radiator heat as needed, and to keep the house at least at 50.
    -- For our 2-adult, 1800sf conditioned area, our energy use is currently 145 therms for gas (water heating, clothes dryer, cooking), and about 250 gal, of oil per average year.

    Specific questions -
    -- Does anyone have a way to estimate the CAE (combined appliance efficiency rating) of the converted gas boiler/indirect water heater combo? I am assuming the gas boiler will run more efficiently than the oil, we are told 20-30%, but that sounds high. No idea how to estimate EF or efficiency of the indirect, except that is supposed to lose less than half a degree an hour such that the boiler may only come on once a day to heat the water in non-heating months.
    -- Based on some energy-use charts, it doesn't look like a new energy-efficient standalone gas water heater would be more efficient than the indirect/gas boiler arrangement, even at the highest .7 EF. Am I wrong?

    Thank you all in advance for any comments of guidance.
    Last edited by embepe; 03-01-2013 at 07:53 AM.

  2. #2
    In the Trades Tom Sawyer's Avatar
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    The conversion is simple and straight forward but if you have a choice of gas burners I would go with a carlin EZ. Adding outdoor reset and an indirect will bring your system up to much better efficiencies and be a lot less expensive than changing it out.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

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    DIY Junior Member embepe's Avatar
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    Oh, good to know... that's what was recommended. Are you saying that using the converted boiler with an indirect would be more efficient than a new, separate gas burner and new, standalone/traditional gas water heater? Thanks.

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    In the Trades Tom Sawyer's Avatar
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    Not more efficient but for the dollar amount saved by changing the boiler the payback would be many many years if at all. You can go here www.nora.com and find free software that will compare various units, efficiencies and costs but having run the numbers and if your estimates are in line the most cost efficient thing would be to convert your boiler especially if its in good shape. For that matter, simply adding outdoor reset and an indirect would most likely be your most cost/efficiency option keeping your oil burner. Gas is less expensive for now but the price will increase sooner or later and gas is always less efficient than oil because gas burns at lower temperature with less btu's than fuel oil. Add the cost of removing your oil tank, and running a new gas service and our payback time increases substantially.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

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    DIY Junior Member embepe's Avatar
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    Thank you - gas service already in place nearby, so hopefully that helps our bottom line.

  6. #6
    Master Hot Water Mpls,MN BadgerBoilerMN's Avatar
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    Your original information is correct.

    Fuel cannot be defined by "efficiency" though choice of fuels can have an effect on the ultimate efficiency of your heating system. For instance, 96% combustion efficiency can easily be achieved while burning gas in one of more of a dozen condensing gas boilers on the market today, all of which feature outdoor reset as standard equipment. Oil boilers, by contrast, and with few exceptions, will fire at about 86% combustion efficiency, if installed, tuned and serviced properly. The operating cost of any boiler is determined by the cost of fuel per therm and the efficiency of the burner plus the control and distribution strategies.

    With a conversion from oil to gas you will enjoy cleaner burning and perhaps longer life of your existing boiler, but you will still have a hot chimney and be drawing conditioned (air you paid to heat up) from the house and mixing it with the byproducts of combustion thence to the atmosphere to condense in clouds...acid rain.

    Your current boiler may last another 20 years with some care, but the combustion efficiency will be in the low 80's. This can and should be confirmed by the technician when he installs the factory approved gas conversion gun. The only way to confirm proper efficiency is with a combustion analyzer. This test will reveal a stack temperature of 350F, about a hundred degrees under the old oil burner and saving about 1% of the fuel.

    Once you have the best boiler you can afford an indirect-fired water heater is the only rational choice. Unlike a conventional tank-type water heater, the typical indirect-fired water heater is simply a storage tank with a heating loop or coil coming off the boiler. Since there is no stack coming off the top of the unit, there is no parasitic draft to cool the heated water between burn cycles. Most are stainless steel and feature foam insulation and as you suggest operate once day or two. Even better, the average indirect will last 30 years--about three times as long as a standard glass-lined tank water heater with standard 6 year warranty. If you don't have soft water you will want a model with a serviceable coil/heat exchanger such as those offered by Crown-MegaStore, NTI-TrinStor and Buderus-ST.

    You may want to consider a new NG condensing boiler with indirect or a combi condensing boiler with built-in domestic water heater such as the Bosch GreenStar or NTI Ti.

    With your low usage, justifying a large investment in upgraded equipment is questionable from a purely financial perspective, but with comfort, fuel usage, longevity and ecology factored in, the choices are not so straight forward. Have your contractor quote the conversion, with ODR and an indirect, but insist on two other options as well. Only the smart guys can give you choices, so which ever you choose, you will generally end up with a better technician.

    "Gas is less expensive for now but the price will increase sooner or later and gas is always less efficient than oil because gas burns at lower temperature with less Btu's than fuel oil."

    Whereas it is true that there is more energy in a gallon of fuel oil than a gallon of propane (an important factor in judging between the two), converting from either to natural gas is rarely a hard choice since natural gas has historically (last 20 years) been a good value and I see no convincing evidence that this trend will change in the next 20.


    http://www.businessweek.com/articles...-cheap-in-2013
    Last edited by BadgerBoilerMN; 03-02-2013 at 06:40 AM.

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    In the trades Dana's Avatar
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    There is even LESS evidence of oil returning to it's pre Y2005 levels, which is what it would take to make gas more expensive, even with a substantial run up in natural gas pricing! The last time 86% efficiency oil was a cheaper way to heat a house than gas (even 80% efficiency, which isn't even legal to install for a new boiler in MA) in New England was in 2002, more than a decade ago.

    At current oil prices it's substantially cheaper even to heat with 25 cent per kilowatt-hour electricity (2x the national average) if you use better-class ductless heat pumps (mini-splits.) There's a chance you'll see $3 oil again (perhaps a fleeting glimpse, if the economy re-crashes) but gas would have to roughly double it's current retail-residential price levels to be more expensive than $3 oil, but the fundamentals that would bring oil that low would also set a new (perhaps insanely) low price point for natural gas.

    No matter who is blowing smoke about oil prices falling simultaneously with rising gas you'd do well to not inhale. While predicting future energy prices is always a fools errand and fraught with error, the price of oil is set by the world demand, whereas natural gas tracks local & regional sources and demand- the cost of liquifying gas for export is a huge cost-adder, which makes gas markets mostly local to the pipeline infrastructure, which is being built up regionally in the northeastern US to get the Marcellus and Utica shale plays to the NY/NE market more cheaply.

    The existing pipelines into southern New England have for decades lacked the capacity for the wintertime peak demands, so half or more of the gas in the Boston area is already the more expensive sort. Most of the fossil-fired electricity in New England is also from natural gas, so in Quincy MA, the retail price of natural gas is ALREADY maximized relative to the rest of the country, and even so it's well under half the per-BTU-delivered cost of heating with oil

    The NORA site indeed has a lot of useful efficiency information on it, but at any efficiency you can't make a rational case for NOT converting to natural gas, if there's a main on your street. The cost of converting a high-mass boiler (even a steam boiler) from oil to gas is paid for in lower heating cost within the first 1 to 1.5 heating seasons almost anywhere in New England. (I have personaly seen multiple real-world examples of exactly that which have occurred within one city block of my house in Worcester MA within the past 6 years.

    Also, by definition all oil boilers are oversized for the heat loads of small or medium sized existing houses in New England, which has efficiency consequences well documented on the NORA site. Without retrofitting heat-purging controls or buying a new oil boiler with those functions built-in, there's no way to actually hit near the tuned-up 86% steady state efficiency as an as-used AFUE. Even breaking 80% isn't in the cards for the typical 3-5x oversizing I see in my neighborhood. See Table 3. You'll note in Table 3 that even at 2x oversizing an 88% AFUE mod-con gas boiler (system #11) hits 85% annual efficiency. A right-sized 95% mod-con will pretty much hit it's numbers if the system designer doesn't bring it to it's knees by micro-zoning the hell out of it, and in the hands of a good designer with more low-temp radiation it can even beat it's AFUE tested & labeled numbers.

  8. #8
    DIY Junior Member embepe's Avatar
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    Thanks to all who answered. (And hello to MN! We used to live in S. Mpls. ... with a giant old beast of a boiler, I might add!)

    I think our approach is going to be to go with the conversion to gas boiler (Carlin EZ) with an indirect water tank attached. The existing Smith boiler has a lifetime warranty and seems to be in good shape. The water heater needs to be replaced anyway.

    Thinking that in 10-15 years we can spring for the best mod-con boiler available then if budget and circumstances allow. The extra $ to fully replace a respectably functional boiler now could be better used (we think) toward other energy improvements that will make the whole house "work" better with the heating energy it uses - i.e., air sealing. The house is already well insulated and our basement pipes all have (encased) asbestos wrap.

    Any pro's / con's on that approach?

    Thanks again.

  9. #9
    In the Trades Tom Sawyer's Avatar
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    i think thats the best approach but then again I said that earlier. Be sure to add outdoor reset to the conversion. I like the Taco PC700
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

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    Master Hot Water Mpls,MN BadgerBoilerMN's Avatar
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    We replaced your old boiler in Minneapolis with a Bosch combi Greenstar last week!

    Every system is limited by funds. A new gas gun and indirect will do a good job as Tom suggests.
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    Last edited by BadgerBoilerMN; 03-08-2013 at 05:23 AM.

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    DIY Member jefferson17's Avatar
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    Default Advice would be appreciated for reasonable estimates etc

    Quote Originally Posted by Tom Sawyer View Post
    i think thats the best approach but then again I said that earlier. Be sure to add outdoor reset to the conversion. I like the Taco PC700
    We're in PA - about 25 miles North of Philly and are in a similar situation. We've got a 10 year old Weil Mclain boiler that is way oversized - 240K. It was there when we bought 4.5 years ago. We can finally get gas now and I've placed the order w/ PECO.

    I've done several detailed heat loss analysis workups and I get about 82000, while trying to be at least a bit conservative. We did a lot of air sealing and insulating this year, starting in the spring. The summer was much more comfortable than prior years. Total sq footage is 2950, 4 levels and 3 zones (zone a is front of house, zone b is middle of house and zone c is rear - only 2 floors not 4). Rear of house also has very new fujitsu split heat pumps, that kept it comfortable solo (that zone was drained out for last 18 months).

    I'm trying to get some quotes from local guys here and would appreciate some basic figures, parts and labor separately - if we go with the following:
    - Carlin EZ conversion
    - Outdoor reset
    - indirect water heater, perhaps a 40 or 50 Amtrol? They seem to be less expensive and ppl say good things about them (current boiler doesn't seem to have integrated connections for this so if we do go w/ one vs. a standalone gas water heater we'd need a small separate circuit built for that). There is plenty of room next to the boiler.

    Also - does anyone have really good figures on recovery value for an indirect water heater vs a high recovery 50 gallon stand-alone gas water heater? We can get a Rheem 42vr50-40f for under $600 delivered.

    Thanks very much in advance, for your assistance!

    Jeff
    Last edited by jefferson17; 09-18-2013 at 03:06 PM. Reason: adding in a bit of info I forgot re heat loss figures

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    Retired Defense Industry Engineer jadnashua's Avatar
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    I'm not sure I believe your heat load analysis! Keep in mind there is absolutely no reason to make it bigger to heat water when you use an indirect; plus, using the design day temperature will keep you warm, especially since two things: the house doesn't immediately become a freezer if it is that coldest day in 100-years, and as long as the boiler you choose is large enough to do it the other 10,000 days, it will likely have some extra capacity anyways, since they are hard to buy at exactly the size you want anyways.

    An indirect will outperform almost any standalone WH (except maybe a few commercial units) since when it does need heat, it gets the full capacity of the boiler (when installed in the normal manner as a primary zone) which is bigger than most standalone burners for WH. Size the thing for your biggest anticipated draw, then let it reheat when it can. Bigger is better if you have say a large soaking tub, or you'll have multiple people showering at the same time, or are using a car wash for a shower (i.e., multiple showerheads).

    If I were a moderator, I'd split this off into your own thread...it's not the best idea to piggy-back others! You may not get the attention since the previous info doesn't apply, people may never get to your question as they get bored.
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    In the Trades Tom Sawyer's Avatar
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    I thought you were a moderator
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Quote Originally Posted by Tom Sawyer View Post
    I thought you were a moderator
    Lost that somewhere along the line...
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Member jefferson17's Avatar
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    I wasn't adding anything to the heat loss calc for an indirect water heater. Those are simply the #s, with some wiggle room that came out of a detailed excel spreadsheet. I didn't trust the "totally accurate" figures I punched in, so I gave the house in the end a design temp of +10 (ODT conversion of .86 instead of +15 (ODT of .79 for 74,735 heat loss). And that gave me the 81356 BTU. Maybe the 74735 is totally accurate but it just seemed a touch low to me, and I was anxious about the possibility of undersizing instead of "1 size up".

    Calculations
    (Factors found in "Heat Loss Factors" Tab at Bottom)
    Multiply x Factor = BTU/Hr
    (A) Window and Doors: 555 Sq. Ft. 39.2 21756
    (B) Net Wall: 2705 Sq. Ft. 10 27050
    (C) Cold Ceiling 1200 Sq. Ft. 1.6 1920
    (D) Infiltration 30300 Cub. Ft. 1.25 37875
    (E) Cold Floor 1000 Sq. Ft. 6 6000
    and/or 0
    (E) Cold Floor 0 Lin. Ft. 0
    BTU per hour heat loss at 0 degrees Outside Design Temp 94601
    ODT Conversion (if other than 0 degrees): x 0.86
    Adjusted BTU / HR 81356.86

    So you are probably correct that my 82K (rounded up) is still high, but unless someone can convince me that sizing to about 75K is still safe, I wouldn't think that I'd use so much more fuel and would sleep better.

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