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Old 09-12-2020, 08:22 PM   #1
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Cracked heat exchanger--coincidence?


So my 110 year old house has the original coal fired, gravity boiler, converted at some point to natural gas. Worked fine all last winter.


This summer, in the course of remodeling my kitchen, I pulled a radiator temporarily, so I drained the system down, shut off the power and gas, and left it empty for much of the summer.



Well this weekend, given how cold it's been lately, I decide it's time to get it up and running, so I put the radiator back and closed the drain, and opened the fill valve. I open a bleeder on a radiator, and for awhile it seems like it's filling, but then it slows before it's full. Go and the basement, and there's water everywhere, pouring out of the combustion chamber. Whoa! Cracked heat exchanger, right? What else could it be?


My question is why did this happen now? Seems like it couldn't be a coincidence that it would crack just when I refill it, but what else could it be? I'm really pretty stumped on this one.


Not looking for a fix. I've been talking to a heating guy and now I just got to light a fire under him to get over here.
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Old 09-12-2020, 08:25 PM   #2
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Re: Cracked heat exchanger--coincidence?


Age and maybe suddenly getting hit by cold water.

Time for a new boiler, your heating bills should drop dramatically. It should have been replaced many years ago.
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Old 09-12-2020, 08:51 PM   #3
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Re: Cracked heat exchanger--coincidence?


Time and corrosion from sitting empty. Possibly thermal shock from refilling.
Either way, shouldn’t be too much of a surprise. New boiler should improve gas usage dramatically.
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Old 09-12-2020, 11:14 PM   #4
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Re: Cracked heat exchanger--coincidence?


Coal is an even fire. Natural gas is more concentrated. It is not uncommon for converted units to fail. It has long passed its expected useful life. Get a modern efficient unit and consider yourself lucky that it didn’t give out the coldest week of the year or on Christmas Eve, when you are at the mercy of the guy who can do it now.
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Old 09-13-2020, 09:34 AM   #5
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Re: Cracked heat exchanger--coincidence?


That's a bummer. It's not often that those old gravity boilers die, but I'd have to say 110 years was a pretty good run.

I would recommend against the urge to replace it with the most efficient thing you can find. Tell them you want a "cast iron sectional boiler". Those are the simplest and longest lasting kind that you can get. Don't get tricked into one of those light weight rectangles that hang on the wall. Despite what the heating company might tell you, they won't ever pay for themselves. They are complex, expensive to fix, and not expected to have a long lifespan.

Before completely giving up on your current one though, make sure the water is actually coming from within the boiler, and not from a relief valve or open vent or drain or something else.

Last edited by bfrabel; 09-13-2020 at 09:37 AM.
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Old 09-13-2020, 10:30 AM   #6
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Re: Cracked heat exchanger--coincidence?


It probably already had a slight crack last winter. And the amount of water leaking was small enough that you didn't notice it. After draining it, and then filling it with fresh clean water, all the debris slowing the leak washed a way.
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Old 09-13-2020, 10:40 AM   #7
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Re: Cracked heat exchanger--coincidence?


Quote:
Originally Posted by bfrabel View Post

I would recommend against the urge to replace it with the most efficient thing you can find. Tell them you want a "cast iron sectional boiler". Those are the simplest and longest lasting kind that you can get. Don't get tricked into one of those light weight rectangles that hang on the wall. Despite what the heating company might tell you, they won't ever pay for themselves. They are complex, expensive to fix, and not expected to have a long lifespan.

Actually, they can and often do pay for themselves. Under the circumstances like the OP's.


In the OP's case, ROI is only based on the price difference of a section cast iron boiler, and the condensing boiler. Not the full cost of installing the boiler.


A cast iron sectional will hold around 26 gallons of water, depending on number of sections. That water will always be heated to heat the house, but never actually be used to heat the house.



A condensing boiler will hold a gallon of water. So the cast iron boiler will be heating that extra water every heating cycle, and then letting that extra heat that was paid for, go out the chimney.



The cast iron will have a min water return temp of either 120, 130, or 140. Meaning that the system water temp must be set higher than needed for most of the heating season.


With a condensing boiler, the water will often only need to be heated to 120F, and seldom over 150F.
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Old 09-13-2020, 10:57 AM   #8
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Re: Cracked heat exchanger--coincidence?


Your big decision will be if you want a 92%+ condensing boiler or an 80-85% non condensing boiler. Do not automatically go for the most efficient, do your research. Look at maintenance and repair costs. Do a BTU calculation or have it done, don't just buy the same size you have now. Here is a link to Weil McLain natural gas, hot water boilers.

https://www.ecomfort.com/heating/wei...r-boilers.html
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Old 09-13-2020, 11:06 AM   #9
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Re: Cracked heat exchanger--coincidence?


For condensing you can get tankless style or conventional.

Here's an example of conventional: https://www.carrier.com/residential/...s/boilers/bw9/

Tankless likely very complicated, loaded with electronics and disposable.
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Old 09-13-2020, 12:42 PM   #10
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Re: Cracked heat exchanger--coincidence?


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Actually, they can and often do pay for themselves. Under the circumstances like the OP's.
They aren't going to pay for themselves if you need to keep buying new ones every 10 years vs. a cast iron boiler that can last 40 years or more with zero issues. Granted now a days most people don't stay in one place for 40 years, so if you don't care how long they last, then I guess efficiency might be the best choice.

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A cast iron sectional will hold around 26 gallons of water, depending on number of sections. That water will always be heated to heat the house, but never actually be used to heat the house.
Unless the boiler is in the attic or outside of the house, then yes it is heating the house. The boiler itself acts like a radiator, which is actually sometimes needed if it's in a cold basement.

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The cast iron will have a min water return temp of either 120, 130, or 140. Meaning that the system water temp must be set higher than needed for most of the heating season.
The old-school boiler makes hotter water, but it runs less often. The high efficient boiler will make cooler water but will run almost constantly. The end result will still be the same amount of btu's worth of heat needed to heat the house (shorter run times vs. longer run times). Granted, the high efficient boiler will use less gas to produce these btu's, but the point I was trying to make earlier is that one breakdown or having to replace the boiler 4 times as often could easily eat up any payback you were hoping to get.

Last edited by bfrabel; 09-13-2020 at 12:46 PM.
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Old 09-13-2020, 01:44 PM   #11
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Re: Cracked heat exchanger--coincidence?


Boilers not used to heat domestic hot water can be cold start. They only heat the boiler water when heat is called for.

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Old 09-13-2020, 02:07 PM   #12
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Re: Cracked heat exchanger--coincidence?


I knew when I bought the house that I needed to change the boiler, obviously. Just an easy thing to procrastinate. I had actually called my guy earlier in the summer, but hadn't pushed it yet. Figured maybe I would skate through another winter, but now I've got some incentive. Yep, glad it isn't January. I've got to get an asbestos removal contractor in there first.



I too am skeptical of payback calculations for high effeciency boilers.. Make great sales pitches, but in reality? In the coldest part of our Minneapolis winter, my heat bill would run maybe $150 a month. Gee, it's going to take a long time to payback that high effeciency boiler unless they start giving me the gas free, and is replacement cost figured in? So it's going to be an atmospheric vent cast iron boiler for me. Plus, I don't have radiators in my basement, it's going to be cold enough down there just getting rid of the monster.
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Old 09-13-2020, 04:03 PM   #13
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Re: Cracked heat exchanger--coincidence?


I would go for efficiency. It is only a matter of time until politicians promising to end fracking get elected, so your fuel bill skyrockets.
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Old 09-13-2020, 07:03 PM   #14
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Re: Cracked heat exchanger--coincidence?


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I would go for efficiency. It is only a matter of time until politicians promising to end fracking get elected, so your fuel bill skyrockets.

Here's a little tidbit that many people might not know... High efficiency boilers are actually only "highly efficient" when running a water temperature below 130F (the temperature at which condensation happens with the flue gas). At water temperatures above 130F, the efficiency is pretty close to the same as a "low efficiency" natural draft boiler (percentages in the low 80's).


Also, cast iron radiators are designed to work best with hotter water (usually around 180F). They might still provide enough heat with cooler water, but I am still a little skeptical that there is a huge amount of energy savings to be had with a condensing boiler vs. a cast iron one.


A cast iron boiler can be set to run cooler water temperatures also (as long as it's not below 130F). An "outdoor reset control" can be had that can adjust the water temperature based on outdoor temperature. These can save energy as well. I would recommend an outdoor reset control on a cast iron boiler over a high tech/high maintenance condensing boiler in most situations.


About the only situation where I actually like high efficiency boilers is with in-floor heat. In-floor heat likes temperatures below 130, so with those there really is an energy savings to be had. Also, in-floor heating systems are almost entirely piped in PEX, which means nice clean water for the boiler. I'm a little leery of sending old crusty water from a 100 year old steel piping/radiator system through the tiny passages of a condensing boiler.
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Old 09-14-2020, 03:46 PM   #15
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Re: Cracked heat exchanger--coincidence?


Quote:
Originally Posted by bfrabel View Post
Here's a little tidbit that many people might not know... High efficiency boilers are actually only "highly efficient" when running a water temperature below 130F (the temperature at which condensation happens with the flue gas). At water temperatures above 130F, the efficiency is pretty close to the same as a "low efficiency" natural draft boiler (percentages in the low 80's).


Also, cast iron radiators are designed to work best with hotter water (usually around 180F). They might still provide enough heat with cooler water, but I am still a little skeptical that there is a huge amount of energy savings to be had with a condensing boiler vs. a cast iron one.


A cast iron boiler can be set to run cooler water temperatures also (as long as it's not below 130F). An "outdoor reset control" can be had that can adjust the water temperature based on outdoor temperature. These can save energy as well. I would recommend an outdoor reset control on a cast iron boiler over a high tech/high maintenance condensing boiler in most situations.


About the only situation where I actually like high efficiency boilers is with in-floor heat. In-floor heat likes temperatures below 130, so with those there really is an energy savings to be had. Also, in-floor heating systems are almost entirely piped in PEX, which means nice clean water for the boiler. I'm a little leery of sending old crusty water from a 100 year old steel piping/radiator system through the tiny passages of a condensing boiler.

Condensing boilers, still condense at 140F.


With cast iron rads, the water temp most of the year can be at 140F or less.



Condensing boilers come in several different types of construction. Stain Less steel. Aluminum, and I believe someone claims to have a cast iron one{not sure on the cast iron).


Many years ago. I did some boiler swap outs at an apartment complex. I installed 2-299,000 BTU input boilers, with a 100 gallon indirect water heater, that took care of 12 apartments for heat and potable water, along with 2 clothes washing machines in the laundry room. And had their own outdoor reset control built into them.



Those boilers used 30% less gas to do the same job as the steel boilers in other building, and the cast iron boilers in still other building.


They liked the fuel savings so much, they had me do 3 other buildings as the old original boilers died.


Those boilers are still saving that complex money today, 17 years later.


I'm only speaking of experience with the ones I have installed, and other ones that I service.


Other contractors, may have had a bad experience.


PS: If your set up is a cold start system, a condensing boiler will heat the house up faster, since its not heating up 26 gallons of water that isn't being used to heat your house.
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