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Determine Boiler Efficiency

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Jsbeckton
Jsbeckton Member Posts: 47
I have a Weil McClain gas boiler is old enough that even WM doesn’t have any info on it such as an efficiency rating. It has a boiler plate that says input of 210k BTU and output of 168k BTU. Does this mean it’s 80% efficient or is that just the heat transfer efficiency?

Trying to determine how much I would save if I converted it to a modern boiler to see if it’s worth considering or not. The boiler is likely from the 50’s and I plan to be here for another 30-40 years.

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  • lchmb
    lchmb Member Posts: 2,997
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    I would start with a heat loss of the building. Once that is known I would see how much baseboard or emitters you have in the building to see if you can run at a lower water temp to increase savings. With that said, it's 65 plus years old.. it owe's you nothing and you would probably see a large saving's if done right... Odd's are it will fail at the worst possible moment..
  • Ironman
    Ironman Member Posts: 7,397
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    No, that's not boiler efficiency.

    See hot rods comments on the current thread about a UFT boiler for good explanation.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Jsbeckton
    Jsbeckton Member Posts: 47
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    Did a heat loss with heatcad and came up with 95k BTU. Will check out that other thread.
  • Gilmorrie
    Gilmorrie Member Posts: 185
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    It is axiomatic that you can't economically justify replacing a boiler that works solely to achieve increased fuel efficiency. Boiler salesmen, of course, will disagree.

    Take my situation, for example. I spend about $1,000 per year for heating (natural gas). If I could replace my boiler with an imaginary one that heats my house with zero fuel consumption, I would save $1,000 per year. To achieve a 5-year payback, I could afford to pay $5,000 for a new boiler - good luck. For my size house, figure $10-15,000, minimum for a new boiler, and it would be lucky to trim my fuel bill by 10-15%,

    Do your own math.
  • Jsbeckton
    Jsbeckton Member Posts: 47
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    My math has me at about $1500/year for heating. If my boiler is significantly oversized and inefficient I’m guessing I might be able to save maybe $650yr with a new boiler and likely more as fuel costs rise. If a boiler will be expected to reasonably operate for 15 years that puts me at about maybe $10k. Seems that might not be enough to make it worth it if a new one might cost more than that.
  • Jamie Hall
    Jamie Hall Member Posts: 23,635
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    As @Gilmorrie just said, you can almost never justify a new boiler on the basis of money, unless it is really seriously old. That Weil-McClain isn't. However, unless it has been well maintained and serviced over the years, you probably can save yourself money -- and some headaches -- by having a really competent technician service it.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • mikeg2015
    mikeg2015 Member Posts: 1,194
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    A combustion analysis will determine efficiency... with excepting to stack losses if there’s no flue damper and standing pilot losses if it has one.
  • Jsbeckton
    Jsbeckton Member Posts: 47
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    Looks like a new ~125k BTU Weil McClain boiler goes for ~$3k, would it really cost $7-9k extra to install for a total of $12k?

    Also, this boiler lasted for ~60-70 years and still works fine. Are the new boilers made so differently that they are only going to last for 15 years?

    It would be a lot easier to justify if it would be a bit cheaper to install or would last longer.
  • NY_Rob
    NY_Rob Member Posts: 1,370
    edited December 2017
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    Jsbeckton said:

    ....this boiler lasted for ~60-70 years and still works fine. Are the new boilers made so differently that they are only going to last for 15 years?


    Modern cast iron atmospheric gas fired boilers should easily surpass 15 years lifespan if maintained properly.

    Maybe you were seeing speculative posts regarding the relatively shorter lifespan of mod-con boilers?

    Keep in mind that on modern boilers simple mechanical aquastats and relays have been replaced with "control boards" that are basically complete computer system on a single board. They also have advanced safety systems that the old boilers didn't have. The added features not only come at a higher price ($500 for a control board vs. $150 for an aquastat) but they add complexity and the chance of more frequent breakdown vs. their old mechanical counterparts.
  • Gilmorrie
    Gilmorrie Member Posts: 185
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    Jsbeckton said:

    My math has me at about $1500/year for heating. If my boiler is significantly oversized and inefficient I’m guessing I might be able to save maybe $650yr with a new boiler and likely more as fuel costs rise. If a boiler will be expected to reasonably operate for 15 years that puts me at about maybe $10k.

    It's an economic fallacy to be satisfied with a 15-year payback because the expected lifetime of a new boiler is longer. You need to look at the return on investment compared to other places to put your money.

  • Jamie Hall
    Jamie Hall Member Posts: 23,635
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    Uh guys... no pricing.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    Canucker
  • Jsbeckton
    Jsbeckton Member Posts: 47
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    Is ballpark estimate of cost of replacement vs living with an old innefficint boiler outside the rules? I guess I took that to mean pricing for a specific job/product.

    If so, then let me rephrase and just ask how many years I should realistically expect out of a WC mod/con boiler vs a new WC conventional boiler and then just do the math myself.

    Thanks!
  • Brewbeer
    Brewbeer Member Posts: 616
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    It's really hard to predict how long a boiler will last.
    I recently installed a new boiler and looked at the economics of the modcon vs. conventional boiler. For my install, there wasn't enough gas savings between the different boilers to cover the higher installed cost and expected maintenance of the modcon.
    Hydronics inspired homeowner with self-designed high efficiency low temperature baseboard system and professionally installed mod-con boiler with indirect DHW. My system design thread: http://forum.heatinghelp.com/discussion/154385
    System Photo: https://us.v-cdn.net/5021738/uploads/FileUpload/79/451e1f19a1e5b345e0951fbe1ff6ca.jpg
  • Gordy
    Gordy Member Posts: 9,546
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    Depends on your maintenance regime. Correct installation, correct sizing, and system water quality/ maintenance. Mod/ con 15-20 plus.
    Ci boiler could be 30 plus.

    Either case could be more.

  • Gordy
    Gordy Member Posts: 9,546
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    I have said this before. Everyone is complacent about the slight savings of a mod/con when fuel is cheap. When it’s expensive everyone wishes they had the higher efficiency.......

    Really it’s more about what we choose to do to preserve our finite resources, but for most those finite resources become the wallet.
    CanuckerSolid_Fuel_Man
  • BobC
    BobC Member Posts: 5,480
    edited December 2017
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    Mod/cons have their place but keeping things simple also has it's place.

    Bob
    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
    Solid_Fuel_Man
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,646
    edited December 2017
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    I agree, as usual there is no clear cut answer. Myself, I take grear pride in the fact that an appliance can use plastic as a flue! Think about that... or you can cook your supper on the smoke pipe of a conventional boiler.

    That said connecting a mod/con to a "builder spec typical" minimum radiated dwelling won't save much of anything.

    It's a sensitive topic as I'm staying with family right now who have a newer home which is defiantly builder spec, with minimal high temp baseboard. In the crawl-space ugh directly below my bed there is a combi Biasi. I listened to it cycle every 5 min all night and the ensuing pex creek as temps swung up and down all night.

    I like to design systems which will provide a good balance of economy and simplicity. CI boilers are wonderfully simple, and work very well on high temp systems. We are in fuel oil country here, and it kills me to see a boiler running at 180 degrees only to mixed down to radiant slab temps running a power flame pripane burner that was retrofitted in to replace oil. A mod/con on a well designed and executed low temp system is a thing of beauty IMHO.

    Rant done....
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
    GordyBobC
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,829
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    I'm not a big Mod-Con guy but they sure run nice. Being able to modulate and reducing stand-by loss is a major savings. It's not all about 82% versus 95% combustion efficiency
    BrewbeerSolid_Fuel_ManGordy