How long should a cast iron water or steam boiler last?

EricPeterson

Well, according to Burnham (US Boiler):

• When properly installed and maintained, homeowners can roughly expect a conventional cast iron water boiler to last 20 or more years.
  

Note: This post is directed towards DIY / homeowners rather than the pros who deal with installs and repairs all the time, to report my experiences with this boiler.

My ES2 install just celebrated its 13th birthday and based on the recent cleaning / inspection, 20 years or more does not seem unlikely. The only wear noticed was some minor corrosion on the exhaust hood (despite their claim of it being made of stainless steel). That may need repair after this heating season. The strip of insulation where the hood connects to the boiler is slightly compromised (new one already ordered from SupplyHouse). Also one of the wires to the thermocouple assembly disconnected during the cleaning - this had been repaired a few years ago but my repair failed, so I simply installed the spare I had (purchased a couple of years ago).

I will say that Burnham did a poor job in the "design for maintenance" - to do the cleaning you have to partially disassemble the boiler. Not fun.

Maintenance history for this boiler:

• 2010: Installed to existing setup, reusing B&G 100, White Rodgers zone valves, B&G compression tank, B&G Inline Air Separator.
  
• 2013: Coupler on B&G 100 failed, replaced with NRF-22.
  
• 2015: no heat, found wire fell off on thermocouple assembly, reattached wire and secured.
  
• 2018: no heat due to failed trace on Option Board, "fixed" with jumper.
  
• 2019: no heat due to failed transformer on Control Board. Fixed by isolating low voltage circuit for zone valves with separate relay (instead of running control through zone valves as documented by WR), replaced transformer.
  
• 2020: no heat - pump was running but boiler was not firing. Control Board was reporting: "soft lockout" Status code=13. Could not find much on this condition, and in the process of troubleshooting the problem disappeared and the boiler started working normally. So this remains a mystery.
  
• 2023: installed Caleffi thermostatic valve, reinstalled Inline Air Separator (it was installed backwards in 2010), add B&G Airtrol ATF-12 - hoping this will reduce / eliminate the persistent accumulation of air at the high point of the system.
  

Overall I have been very satisfied with this boiler.
The one upgrade I am considering now is outdoor reset. Burnham claims in their brochure that:

• "Outdoor reset available – increases efficiency by 15-20%".
  

I don't know what this means and if it's worth it. The option board for this is pretty expensive. I don't mind the expense if it would really make a difference:

• How much will it increase the current stated efficiency of 85%?
  
• How much it might decrease my gas bill of around $1500 for last year's heating?
  

Thanks for reading,
Eric Peterson

Gilmorrie

It is commonly accepted that replacement of a boiler that still works reliably can't be justified based on projected fuel savings. Boiler salesmen will disagree.

Expecting 15-20% increase in efficiency by adding outdoor reset is, I think, probably a pipe dream.

hot_rod

Tekmar mostly pioneered the microprocessor based ODR
Honeywell had a simple dual cap tube control maybe in the 1960s

tekmar claims 5-30% savings. I do agree comfort can increase with a more steady state running

https://www.watts.com/our-story/brands/tekmar/references/how-outdoor-temperature-reset-controls-save-energy?gad=1&gbraid=0AAAAADA6ga521rzurc6lE0ndC8A6up-hn&gclid=CjwKCAjwp8OpBhAFEiwAG7NaErr9UtCWFRA2G0HB6PQ6Zj4qQdwIZsCHyKS50bXE8a19Os1VUTefxhoCBzcQAvD_BwE

Im not convinced the cast boilers being built today are 25- 50 year products? The certainly have been made smaller and lighter.

Reminds me of the Ray condensing cast boiler. The concept was a thick casting and let it corrode away go 20 years or more 

So either they crunched the numbers, or played the rule of odds

EricPeterson

hot_rod said:

Tekmar mostly pioneered the microprocessor based ODR
Honeywell had a simple dual cap tube control maybe in the 1960s

tekmar claims 5-30% savings. I do agree comfort can increase with a more steady state running

https://www.watts.com/our-story/brands/tekmar/references/how-outdoor-temperature-reset-controls-save-energy?gad=1&gbraid=0AAAAADA6ga521rzurc6lE0ndC8A6up-hn&gclid=CjwKCAjwp8OpBhAFEiwAG7NaErr9UtCWFRA2G0HB6PQ6Zj4qQdwIZsCHyKS50bXE8a19Os1VUTefxhoCBzcQAvD_BwE

Im not convinced the cast boilers being built today are 25- 50 year products? The certainly have been made smaller and lighter.

Reminds me of the Ray condensing cast boiler. The concept was a thick casting and let it corrode away go 20 years or more 

So either they crunched the numbers, or played the rule of odds

Well if the chart is correct, my payback would be 1 to 5 years. So probably worth it.


The boiler I replaced (a Crane Bastian-Morley) was 56 years old and still working. The only issue was some of the mantles on the burner manifold had failed, and about 25% of them were capped off. It was not leaking. It did have a pilot light and lacked a vent damper.
It certainly lacked any protection against low-temperature return water, I can tell you that.
It was not well maintained either - at one point there were flames coming out the bottom because the passages were clogged with soot.

The ES27 weighs in at 464 lbs with a 6 gallon capacity, that doesn't seem a whole lot lighter than the one it replaced, which was a little larger. Time will tell I guess. The good news is that Burnham is still making this model. I don't know when it was introduced but I suspect sometime around 2008 or earlier, so that would be at least 15 years in production.

Eric

jesmed1

We have two 25+ yr old Weil McLain WGO-5 cast iron oil-fired hot water boilers. They're still going strong, at 760 pounds each, according to the brochure, and they're still being made.

EBEBRATT-Ed

ODR will not save enough money to make it worthwhile

fentonc

I think the benefits of ODR are just going to be extremely system and location dependent. Given a more or less constant combustion efficiency, my understanding of lowering the SWT is that there is a small efficiency benefit from the higher delta-T between the water and flue gases, and a much larger benefit from lowering 'overhead' losses associated with heating up the boiler and any water in it, and then having much of that heat leak away into the immediate area around your boiler and/or up the flue. If nearly all of that heat were dissipating into conditioned space, the benefits would be significantly smaller. If your boiler is located in a space where most of that heat is lost to the surroundings without benefiting the conditioned space in the home, you save much more. And all of that gain is going to be multiplied by how oversized your system is relative to your weather, and what fraction of the total energy in the system is stored in the boiler.

As a thought experiment, imagine a system with a high mass boiler (lots of iron, lots of water) in a completely unconditioned place like a garage, but with a very low mass distribution system like fin tube. It's 60F outside, the thermostat calls and the boiler + water is heated to 180F (120F delta-t). The thermostat is satisfied as soon as the water hits 180F, and the boiler cools back down to 60F before another call. If the SWT were 120F instead, the boiler-garage delta-T would only be 60F instead of 120F (50% lower), and 50% fewer BTUs would be stored in the boiler and lost between cycles.

My CI boiler is oversized for the amount of fin-tube I have and my fin-tube is wildly over-provisioned for the actual heat loss of the house at the design temp (at least at 180F), and the boiler is located in an uninsulated mechanical room where little of the residual heat usefully makes its way to conditioned space. I was able to just permanently lower the water temp from 180F to 150F (along with some tweaks to thermostat setbacks), and my average gas usage per heating-degree-day did reduce by ~15% or so (not sure exactly how much of that was lowering the SWT). If your system is oversized, you can probably get much of the benefit just by statically lowering your SWT (or maybe adjusting it once a month or something) if you don't want to spring for the ODR sensor.

jesmed1

You might also consider installing a Field Controls automatic vent damper. Our two oil-fired boilers are in a basement where I have my shop set up, and the basement gets cold because the wind is constantly sucking heated air up the flue when the boilers aren't running. Which is most of the time. So one of the upgrades I'd like to make eventually is to install automatic vent dampers on both boilers. Some users say it makes a big difference in preventing heat loss after boiler shutdown.

EricPeterson

@fentonc - great points. The boiler is located in the center of the basement in conditioned space. So most of any lost heat simply migrates to the three floors above the basement.

@jesmed1 - the boiler already has a vent damper which seems quite effective as the boiler retains heated water for hours, with residual heat migration blocked by the zone valves. The boiler is located adjacent to an atmospherically vented water heater lacking a vent damper, so heated air does escape that way. There is also a fresh air inlet adjacent to this equipment area.

Since I have recently installed a thermostatic valve on the boiler, ODR settings would have to be done carefully to avoid the boiler ending up in a cycle where water simply loops through the boiler.
Right now the valve has a 140F thermostat, meaning the valve starts opening when the return water is 140F and fully opens at 158F. So if the ODR dictated a setpoint of say 120F well then the system would never heat up.
The factory setting for the high limit is 180F.
Assuming a 20F rise through the boiler suggests to me that the high limit should be lowered only slightly, to 178F, for the 140F thermostatic element.
There is a 115F element available but even then the return water would have to be 133F before the the valve opened fully.
With the 115F element, by this logic the low setting on the ODR would have to be 115+18+20, or 153F.

So based on the boiler location and the valve, yes it would seem possible that ODR would not save a whole lot.
BUT if I knew it would last say 10 more years THEN it might be worth it.

Eric