Thermal Shock!

 
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dbsuz05
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Post by dbsuz05 » Wed. Feb. 26, 2020 1:05 pm

I have some questions on thermal shock.
I run my boiler system on 24/7 circulation. So therefore I believe I am in the clear on detrimental cold water hitting the interior walls of my boiler.
But my question. Is..... if your boiler is always sitting at 160-180. And you don’t have a call for heat for say 8 hours?... warm day.. the return water is obviously gonna be about 70 degrees at best. Does this happen to any of you guys boilers? What’s your opinions? Thanks!!


 
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coaledsweat
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Post by coaledsweat » Wed. Feb. 26, 2020 2:32 pm

Find something else to worry about.

 
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Lightning
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Post by Lightning » Wed. Feb. 26, 2020 2:38 pm

Mr. Coaledsweat is often a man of few words, albeit sincere words in the least.. boiler shock isnt a problem unless you have a huge volume of cold water coming back to the boiler. From a series of many cast iron radiators for example..

 
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Post by dbsuz05 » Wed. Feb. 26, 2020 2:41 pm

coaledsweat wrote:
Wed. Feb. 26, 2020 2:32 pm
Find something else to worry about.
This cold water is returning to a old cast iron round boiler.... still just forget about it? No chance of ever cracking the cast?

 
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Post by coaledsweat » Wed. Feb. 26, 2020 2:51 pm

The boiler is how old? And being hit with cold water all that time?
You're running the pump full time so it isn't seeing much shock at all I would think. Am I wrong?

 
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Post by dbsuz05 » Wed. Feb. 26, 2020 3:53 pm

coaledsweat wrote:
Wed. Feb. 26, 2020 2:51 pm
The boiler is how old? And being hit with cold water all that time?
You're running the pump full time so it isn't seeing much shock at all I would think. Am I wrong?
Not sure of boiler age. 20’s? Round burnham boiler... no it’s not getting hit with cold water all the time. Because of my constant circulation. But being that I have a axeman 130 now. Instead of constant circulation I was thinking of making it start and stop when there’s a call for heat in the house. I’ve just been running axeman at 120 during warm days. And then cold times I’ll put it at 150 or so So it’s sort of running like it’s heating dhw.

 
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Post by coaledsweat » Wed. Feb. 26, 2020 4:07 pm

You shouldn't run a boiler at 120°. The water will be full of oxygen and it will eat the boiler. At 153°, oxygen disassociates from water. I don't reccomend anything lower than 140°. Thermal shock isn't a problem for you, not sure why you think it is. A steam boiler full of mud? It's a problem. If you are still concerned about it, plumb it with a primary secondary loop.


 
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Post by lsayre » Wed. Feb. 26, 2020 4:42 pm

I always thought that thermal shock was a concern for cast ion boilers, but little to no concern for steel boilers.

 
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Post by dbsuz05 » Wed. Feb. 26, 2020 4:55 pm

Well I just thought of cold water at 70 degrees. And a boiler at 160-180. That temp difference was considered boiler shock. The rads are all piped with primary secondary. Monoflo tee.
So the cold water isn’t instant from 15 rads all at once.

 
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Post by dbsuz05 » Wed. Feb. 26, 2020 5:24 pm

coaledsweat wrote:
Wed. Feb. 26, 2020 4:07 pm
You shouldn't run a boiler at 120°. The water will be full of oxygen and it will eat the boiler. At 153°, oxygen disassociates from water. I don't reccomend anything lower than 140°. Thermal shock isn't a problem for you, not sure why you think it is. A steam boiler full of mud? It's a problem. If you are still concerned about it, plumb it with a primary secondary loop.
I know you have said before about the oxygen disassociates below 153.
But what about people that run handfeds? I’ve seen them run at 120 all the time. There’s almost no way possible to keep a handfed above 153 always. Unless I would be the “iron fireman”!!
So with that said. You don’t believe that a cast iron boiler could crack with water temp difference 80 degrees? Thanks for your input sir!

 
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Post by coaledsweat » Wed. Feb. 26, 2020 5:45 pm

ABOVE! Above 153°. Going down to 140° doesn't suck up a lot and it will be gone at 153°. 120° is asking for it. I never had trouble keeping a hand fed at 180°. Unless it is to undersized for the load maybe?

No, I don't think it will crack.

 
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Post by dbsuz05 » Wed. Feb. 26, 2020 5:56 pm

I wouldn’t say the boiler is undersized. It’s a 23” round. But after 9 hours of constant heat output. The house and garage have always been warm. But possibly because of constant circ.. that is why handfed never really wanted to stay up above 153 for long term... it just sucked the life out of it! That is why I added the axeman this year though. So I do believe I have more than enough firepower now! I am gonna try to run circulator off the axeman aquastat this weekend. That way axeman stays hot. The return from house goes to handfed then down to the aa130. Circ will only run when house calls for heat then. I hope to make this work alittle better than just running aa low aquastat temp and adjusting temp by the outside temps by the day.

 
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Post by Sting » Wed. Feb. 26, 2020 9:09 pm

coaledsweat wrote:
Wed. Feb. 26, 2020 2:32 pm
Find something else to worry about.
That's rather harsh for a mod to post ????

 
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Post by Sting » Wed. Feb. 26, 2020 9:10 pm

dbsuz05 wrote:
Wed. Feb. 26, 2020 1:05 pm
I have some questions on thermal shock.
I run my boiler system on 24/7 circulation. So therefore I believe I am in the clear on detrimental cold water hitting the interior walls of my boiler.
But my question. Is..... if your boiler is always sitting at 160-180. And you don’t have a call for heat for say 8 hours?... warm day.. the return water is obviously gonna be about 70 degrees at best. Does this happen to any of you guys boilers? What’s your opinions? Thanks!!
Someplace in the background are seveal threads on boiler protection
Should answer this
Kind Regards
Sting

 
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Post by coaledsweat » Wed. Feb. 26, 2020 9:26 pm

Sting wrote:
Wed. Feb. 26, 2020 9:09 pm
That's rather harsh for a mod to post ????
What do you recommend to replace it with?


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