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Condensing vs traditional cast iron boiler?

darrylg Member Posts: 15
I am switching from oil to natural gas, and National Grid offers discounts on Burhnam boilers. I am debating on purchasing the Alpine modcon vs one of their traditional cast iron boilers. Is there any reason I should choose the Alpine?

I've performed a cost-benefit analysis and financially the cast iron is much cheaper over 25 years, assuming the condensing boiler needs to be replaced after 12-15 years.

Any thoughts before I go ahead and order the cast iron 85% efficiency unit?


  • SWEI
    SWEI Member Posts: 7,356

    What kind of emitters are installed, and do you plan to leave those in place?  Then you need a room-by-room heat loss to pick a system design temp.  From there, a better comparison can be made.  
  • Robert O'Brien
    Robert O'Brien Member Posts: 3,483
    Cost /benefit?

    You need to project the price of natural gas out to 2037? Since 1967,the average price increase is almost 5%/year. If I knew what the price of gas was going to be next month much less 25 years from now,I'd be trading NG futures from my yacht in the Caribbean! Seriously,you also have to account for the eff. difference and it's way more than the 10% AFUE spread would suggest
    To learn more about this professional, click here to visit their ad in Find A Contractor.
  • CMadatMe
    CMadatMe Member Posts: 3,086
    Then Why Buy

    A condensing boiler that's only going to last as long as you predicte and buy one that is made to a goal of 40 years? Could you share with us your cost analysis? How did you account for the modulation rate of the condensing boiler over the fixed rate of the cast iron boiler? Cause the condensing boiler isn't firing at the same btu rate every day. When its 40 degrees outside the condensing boiler may only be firing at 40,000 btu/hr while your fixed rate cast iron boiler is firing to what it is..
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • Roland_18
    Roland_18 Member Posts: 147

    Don't forget the cost of yearly service. From what I've read here, mod-con boilers can be more expensive to maintain due to added complexity.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    Annual service cost.

    I suppose I should not post what my service contract costs for my W-M Ultra 3 boiler and indirect domestic hot water heater. It is gas fired.

    But the maintenance contract for it costs less than the one I had for my old oil-fired boiler. My current contractor charges more for oil-fired boilers than for gas fired ones. And I do not know if he charges more for mod-cons or not. I did not really care what he charged, provided he did the work.

    My current contractor drew up this contract specifically for me. It is itemized, and one of the items reads:

    1 Weill-Mclain Ultra 80  Boiler Service each Year  per manufacturers requirements. And they do it (except for checking the relief valves). Check the boiler water, open and clean the heat exchanger (using my torque wrench to tighten the bolts when done), replace the igniter (not sure why, inspection is all that is required; probably it is cheaper than a free no-heat service call at inopportune time) using all new gaskets, clean condensate trap, stuff like that.

    I kept the old igniter because it looked brand new. It did not even need cleaning.
  • darrylg
    darrylg Member Posts: 15
    Thanks guys

    Obviously when performing a cost benefit analysis, you need to make a lot of estimates and assumptions, so here is what I used:

    Gas price increases @ 1% per year. I looked at the last 12 years of natural gas prices in my area, and they've actually decreased by 16% since 2001. So I figured I'll play it save and account for a 1% increase.

    Estimated usage: 2000 therms/year (very generously)

    Condensing boiler lifespan: 12-15 years

    High efficiency Cast iron lifespan: 25 years

    I have used the AFUE rating to determine my cost savings between the two units. Now I see that may not be the best method to use, but it should be fairly close. If it's not using 10% less fuel, would it be closer to 20% less? I also assumed the AFUE rating accounted for the modulation and ODR, so that's probably something else I should consider.

    The cost of gas for the 85% boiler for 25 years @1% increase per year =$45,471.55

    The cost of gas for the 95% boiler for 25 years @1% increase per year =$41,517.50

    Which is a grand total of = $3954.05 savings

    Now consider the 95% unit costs an additional $2,000 up front and $6,000 in 12-15 years for replacement, and the savings does not even come close. Figure in an additional $100/year for service and the condensing boiler has an additional cost of $10,000 vs the $3954 it is saving.

    The only way the condensing boiler seems to make sense, is if it's actually 25% cheaper to operate than the cast iron, natural gas increases 8% each year for 25 years, or the lifespan of the condensing unit is 25 years. Basically spending $6000 every 12 years really eats into any savings. It doesn't seem like they are ready for prime time yet..but I'm no expert, just looking at it from a financial stand point of view.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    Gas vs oil.

    I do not know if my numbers are much use, but here are some.

    At my current billing rate, including all charges, my gas bill is little less than $400/year (for the past 12 months). The gas company charges me $2.48/therm for gas, and $2.19/therm for delivery. They also charge $8.25 monthly customer charge. I run the boiler all year because it runs my indirect hot water heater.

    From 1976 until 2009, I used oil in an old GE oil boiler. Depending on the weather I used 300 to 600 gallons of fuel oil per year. Way back when, the stuff was about $0.40/gallon, and it was almost $4.00/gallon near the end.

    I had a 1000 gallon tank that was filled once a year, except I did not have it filled the final year at all.

    Bills were

    2006-06-14 480.1 Gallons 1,425.90

    2007-06-23 516.9 Gallons 1,535.19

    2008-06-16 410.3 gallons 1,875.07

    So my bills dropped about 75%. How much of that was the lower cost of gas, the fact that I had a new boiler instead of the old one, and how much of that was due to mod-con boiler with outdoor reset I do not know.
  • darrylg
    darrylg Member Posts: 15
    are your rates really that high?

    I'm making my cost basis from national grid's prices, and we typically have the highest rates in the country for utilities:

    Aug 1 2012

    Monthly Cost of Gas = $0.4209/therm

    Delivery: First 3 therms or less : $13.6600

    Next 47 therms: $0.6320

    Excess 50 therms: $0.2000
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    are your rates really that high?


    Think, and the world thinks with you.

    Gafoo, and you goof alone!

    Those numbers are the cost per therm multiplied by the therms I used that month.

    Gas is $0.5837/therm

    Delivery $0.5155/therm.
  • gennady
    gennady Member Posts: 839

    Just make sure your new boiler has a standing pilot because electronic ignition is more expensive and can go bad in a 20 years. Also, there are boilers like Williamson and Crown, they are much cheaper and quality wise are on par with brand name boilers. Can't beat that. Make sure you hire lowest priced contractor. They are also all the same, just some are greedy, and others are good guys.
  • CMadatMe
    CMadatMe Member Posts: 3,086
    Real Numbers!!

    The average customer that has a condensing boiler properly installed will see 35% fuel savings easily. That is a conservative number. Get off the yellow tag on the boiler its mean absolutley nothing..Figure this out...

    1 gallon of condensate produced by a condesning boiler saves 8,000 btu/hr that your 85% boiler can't do...

    A condensing boiler is NOT using a fixed btu/hr rate. Your 85 is..

    Your drinking the wrong cool-aid...But what do I know....
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
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