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Choosing between high efficiency and cast iron boiler

alexholman Member Posts: 5
We're having our boiler replaced and could use some advice choosing between a high efficiency and cast iron boiler. We have a single-family house in New England, 1500 sq/ft, insulated walls, with hot water baseboards and a 40gal super store. The two options that were recommended by our plumber are a Lochinvar KBN080 high efficiency and a Burnham ESC3NI-TS cast iron. With a state rebate the HE system only comes in about two or three thousand more expensive than the cast iron.

Theoretically, the HE system would save on fuel cost, as its 95% AFUE vs 85% for the cast iron. However, the HE furnace would require yearly maintenance that's more expensive than the cast iron, and according to my plumber, the cast iron could go with maintenance every other year for the first 6-8 years. I feel like this would pretty quickly wipe out any fuel savings between the two.

Also, in terms of lifespan, I'm told that the cast iron has an expected lifespan of 15-30 years, whereas the HE system is 10-15 but has yet to be proven. Again, wiping out any cost savings of the HE furnace, as I plan to grow old and die in this house.

What I'm wondering is, given these points, is there anything I'm missing that would make me go with the HE boiler, because right now everything I'm seeing is pointing cast iron and eating the additional fuel costs, but with a greater savings overall.

Additionally, if I go with the the cast iron system, I have the options of an outdoor reset card, and a touch screen (both for additional costs). We have 3 zones in the house, and tend to only heat the zones we're occupying at the time. Would the outdoor reset do much for us in terms of comfort and efficiency, or is in not worth the extra cost?
Also, I'm a bit of a hands-on guy, and like to troubleshoot problems myself. Does the screen on the burnham get me a useful interface, or is it mostly just shiny blinky lights?



  • NY_Rob
    NY_Rob Member Posts: 1,370
    Did your contractor do a heat loss analysis?
    Can you post the results?

    Do you have your (actual no estimated) gas usage for the past couple of months?

    What is your location, and age of house?
  • vvzz
    vvzz Member Posts: 39
    I'm not a professional, so take my advice with a grain of salt. Keep in mind that high efficiency mod con boiler will need to be properly sized, installed and configured to operate at 95% efficiency. If it's oversized(it happens alarmingly often) and has outdoor reset disabled, then it will almost never be operating in condensing range and achieving 90+ efficiency.

    So in your case cast-iron boiler seems to be more preferable. Definitely go with outdoor reset card. There's no sense to heat that water to 180 when 150 can do.

    However, if a mod con is installed correctly and sized well for the application, it will definitely be a much more comfortable system with virtually no interior temperature fluctuation.

    In any case, make sure the installed performs a full heat loss calculation of the building and only sizes the boiler based on that.
  • John Mills_5
    John Mills_5 Member Posts: 935
    The national trainer for a leading boiler brand said he feels cast iron is often the wisest choice for baseboard heated out. Takes a long time to recover the premium for the 95% over the 85% in gas savings. 1 repair of the very complex mod con will more than eat up any savings over the life of the boiler. I'd sure get the longest warranty possible with a mod con.

    For gas furnaces, the premium for a 95% over an 80% is minimal. We rarely sell 80% furnaces unless it's a rental or we can't vent a 95%. Too bad mod con boilers are so salty priced.
  • Docfletcher
    Docfletcher Member Posts: 481
    I'm in very much the same dilemma as alexholman right down to the house size . I've pretty much given up on the idea of HE boilers and am now thinking along the lines of a Burnham ESC3. I feel it's life will be appreciably longer without the costly maintenance. Admittedly, I have no empirical evidence to support my contentions with the matter. My assertion here is based upon what I've seen and heard through the scuttlebutt channels that abound on the internet coupled with my experience with the longevity of my current cast iron boiler.
  • alexholman
    alexholman Member Posts: 5
    edited April 2016
    Here's the numbers on our historical gas usage. Keep in mind though, that our previous boiler was way oversized.

    I'll make sure to follow up with the plumber about doing a full heat loss calculation for us in sizing the boiler.

    Location is Boston, and house is 1905 or so (though we recently had insulation blown into the walls).
  • NY_Rob
    NY_Rob Member Posts: 1,370
    Do you have the figures on the length of finned tube for each zone? Not the length of the zone loop from the boiler output to the boiler return but the actual sum total length of the finned portion of each radiator that makes up a particular zone...
  • billyboy
    billyboy Member Posts: 152
    I would go with the ESC3
    (I am not a pro, just opinionated DIY'er)

    With high temperature emitters a modcon will be 8% or so below the advertised 95.2% efficiency.

    The KBN081 costs much more than the ESC3

    The KBN081 yearly maintenance costs much more than the ESC3

    The KBN081 will most likely need to be replaced way before the ESC3
  • Chester
    Chester Member Posts: 83
    The first thing is to determine what water temps you're going to need to supply your baseboards with to keep the house comfortable. So you need to know your design day heat loss and then calculate the EDR of your baseboards, like NY_Rob says.

    ModCons only start to achieve condensing efficiency when the return water is around 130F. You might not see the magic 95% combustion efficiency until you get to much lower return water temps, at which point your baseboard might not be performing adequately. It'd be a different story if you had cast iron radiators or installed new panel rads or other low-temp emitters.

    Baseboard is typically designed to run at 180F supply. You'll never get the benefit of the condensing efficiency unless you have enough baseboard to run much lower water temps.
  • SWEI
    SWEI Member Posts: 7,356
    What are your fuel costs like?

    The KBN is an old design which requires more frequent maintenance than newer ones -- if the plumber is recommending it, I would suggest you consider speaking with another contractor.
  • Dave19
    Dave19 Member Posts: 28
    I went from a Smith to a Vitodens 200 with an outdoor reset (not the same comparison exactly but) my gas usage was cut in half. Living in NH in a 2200 sq ft home. The Viessmann out of the box on high fire is only 88% and so are the rest of these mod cons claiming 95. I've done my fair share of efficiency testing and never seen 95%....ever. But that outdoor reset makes a big difference. On a 20 degree day I think I'm heating with 140 degree water (roughly). That being said I would go with the Lochinvar of those two choices, but personally I would only buy a Viessmann
  • Gordy
    Gordy Member Posts: 9,514
    Low to mid 90's is attainable with the right emitter that being radiant done right.
  • Gordy
    Gordy Member Posts: 9,514
    When you say your gas bill was cut in half. How much of that was contributed by the boiler being more closely matched to the heat loss?
  • billyboy
    billyboy Member Posts: 152
    OP "with hot water baseboards"
  • jumper
    jumper Member Posts: 1,710
    The simpler the better. Energy is not expensive. Service is.
  • Gordy
    Gordy Member Posts: 9,514
    edited April 2016
    no energy is not expensive now. However we are not fortune tellers, and since the appliance has a life expectancy of a decade times 3 energy should be considered as expensive.
    JUGHNE Member Posts: 8,943
    With one job I had I would have used the cast iron but the condition of the existing brick chimney was the deciding factor. It was an inverted Wye configuration with no liner possible....2 1/2 story steep roof.

    We ended up with the KBN. The older HO wanted to "feel" the heat from his cast iron rads. So we run at higher temps than needed and the condensing advantage is mostly lost.

    I'm sure his heating bill is less, but this is a coffee ground producer and will require a cleaning every 2 years for certain.
    The KBN is a water tube condensing boiler. From what I read and hear the fire tube design has less cleaning requirements.....also perhaps one less pump needed.
  • bob eck
    bob eck Member Posts: 928
    There are gas cast iron boilers that are 84% - 85% AFUE then 90% AFUE that are reasonably priced equipment then there are the 95% AFUE condensing high efficiency higer priced boilers. You need to get a proper heat load of your house. Then see how much copper baseboard you have so you can see how low of a water temp you can run on days where the system is running at design temp. High efficiency condensing boielrs are only at their highest efficiency when running low water temps. You could install a Burnham cast iron boiler and still get outdoor reset with installing one of their cards in the boiler. With cast iron gas boiler you have proven relibality of boilers lasting 20-30 years or longer with proper installation and maintenance. There is boiler AFUE efficiency but you also need to look at how the heating emitters are designed. If any of these boilers are to large for what ever reason and they short cycle run for very little time when heat is needed your efficiency goes out the door. Plus the higher efficiency units when something goes wrong the cost to repair them is high. See if you can buy a boiler with 5 or 10 year parts warranty. Most heat exchangers on the high efficiency boilers have a 10 year warranty and most cast iron boiler heat exchangers have a 15 - 25 year warranty on the boiler block. These warranty are only for manufacturer defects not if they leak because of not being installed right according to the manufacturers installation instructions.
    Dave H_2
  • BigRob
    BigRob Member Posts: 297
    Check the Lochinvar service manual for the coil HX models- says to clean the coils once the exhaust temp reaches a certain level compared to outlet water temp. Besides checking the neutralizer and flame window every once and a while these units are pretty solid. The new floor fire tube units look awesome. Anybody, please let me know what PM you do. I'm curious. We condense a lot all the time at 20% fire and 120 return- but we are located in a marine environment.

    With that said, a modulating cast iron would be awesome if you need the flexibility. Like others said, if your setup has high return temps the added cost of a mod con is uneccessary. In that case I think the reverse indirects paired with a cast iron are awesome- buffer tank and hot water in one tank. Two Alphas and zone valves and you are done. You could even use a mod con and condense with some tinkering.
  • Jamie Hall
    Jamie Hall Member Posts: 17,060
    You might want to check out the fairly extensive commentary on high efficiency vs. others on the thread

    It's stretching it a bit, but the weight of the comments is that unless things are exactly right, HE boilers are a somewhat dubious choice...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Jason_13
    Jason_13 Member Posts: 299
    Either boiler you choose needs to be sized properly. Even though I prefer mod/cons in any application I can argue the point both positive and negative on either side. I will start with the mod/con.
    1. ODR is included, no extra charge. With most wireless sensor can be an option
    2. Modulation, A mod/con boiler will reduce the input as needed. I have heard that a mod/con will operate in the lower half of the input 60% of the heating system
    3. More important to properly size due to higher off cycle losses
    4. Proper sizing gives lower turndowns for smaller zones
    5. More expensive parts
    6. More maintenance
    7. Low return temps without worry, condensing a good thing
    8. As water temperature increases takes a bigger hit on efficiency
    9. Must be set up with a combustion analyzer
    Outdoor air for combustion

    Cast iron (ESC since OP mentioned it)
    1. Need to be properly sized since
    2.Full input only
    3. ODR extra option
    4. Can use wireless OD sensor, btw, same price as wired sensor when orderded with the ODR card, little known fact
    5. less maintenace
    6. Thermal mass and higher water volume a plus
    7. Cannot return less than 110f, condensation bad
    8. Starts with a lower efficiency but takes a smaller hit as water temperature increases.
    8. Should be checked with a combustion analyzer

    Maximize efficiency of both products
    1. Proper size
    2. Combustion air from outside
    3. Do the math and calculate the high limit setting
    4. Calculate the minimum boiler setting and set the ODR parameters including minimum boiler settings
    5. Pipe the products per the I&O manuals that come with the products
    6.Do not make too make small zones
    7. Check incoming gas pressures whlie boiler is in high fire to meet spec's.
    8. Don't over pump the system or boilers