Thermal Shock and Automatic Feeders.

Joseph_4

I've read in many places that you need to be careful before adding  water (assuming your water fill is cold water and not piped from say the hot of a hot water tank) because you can crack the cast iron sections. I was wondering about this. During anytime a home owner adds water why doesn't he have to worry about this.

Also by an automatic feeder, it adds when it senses low water and doesn't wait for boiler to cool down, why isn't there a possibility of it cracking through thermal shock?

Thanks

Joe

Jamie Hall

It might

except that an automatic feeder shouldn't be adding that much water at a time, depending on the size of the boiler, so the temperature drop by mixing isn't that much.



However... if one has a significant failure, and the boiler is running, and the feeder just keeps adding cold water chasing after a biggish leak (you do have a Hartford Loop, don't you?) then you could indeed have a problem.



Again, many automatic feeders have lockouts to prevent that, though -- after so and so many gallons, they just lock the system out and wait for someone to figure out what went wrong...

BobC

Thermal shock

I don't have an auto feeder on my boiler so I can choose when to add water. I try to add water at the very start of a burn cycle so the boiler is only warm and i know I'll burn off any dissolved oxygen caused by the added water. I've been doing this for 40 years with no problem.



If I do have to add water to a hot boiler i just crack the valve and let the water enter slowly so i don't shock anything. I don't know what rate the auto feeders add water so I can't really comment on any problem they might cause but I have to say I've never heard of any problem caused by them.



Bob

Bob Daros

Water Feed

I pipe my water feed into the return on the house side of the Hartford Loop.

This blends the now cold water with the warmer return water so it is not such a shock to the boiler. You should also use a timed auto feeder.

When ever we do steam boilers, we redo as much of the return piping which makes the installation of a tee very easy.

Brian_74

So why not pipe from DHW?

Even though the odds of damaging the boiler from thermal shock seem to be low, they're not zero. So why doesn't the fresh water come from the water heater?

crash2009

They put mine here

There must be a reason.  They put mine into the return,,,way back from the Hartford.  Its about level with the bottom of the boiler.  It looks to me that it would fill the return first and the weight would push preheated water into the boiler.  see pic red dot.