Boiler Temp Return

[wenger7446]

Why must a boiler return be 140 or so degrees? I understand how a 4 way mixing valve works but I do not understand why one is needed.

Thanks in advance.

 

[Eric Johnson]

If the water at the return gets below 130 or 120 for extended periods, it will cool the inside of the firebox so much that you get condensation, which reacts to the acids in the creosote and other combustion products and corrodes the metal. Over time (years), enough steel will flake off into the firebox that it becomes paper thin, and eventually either cracks or springs pinhole leaks. And that's the end of the line for your boiler.

 

[Nofossil]

It's a fair question whether the critical temperature is 120, 130, or 140. My supposition is that if you idle a lot or burn wood with higher moisture content, then your flue gas would be more likely to condense and cause problems, and you'd want to maintain a higher inlet temperature.

 

[Rancherii]

For a bit of added information, given the right conditions with a low water return and Unusually corrosive ash, problems can occur sooner then one would expect. Heed all warnings in regard to low boiler water return. Just my two cents.

 

[wenger7446]

Great! Thanks to everyone who responded!