Historic Home Radiant Hot Water

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Permalink Reply by tedkidd on June 30, 2011 at 10:16am

Cast Iron Radiators LOVE modulating condensing boilers.  This is a great opportunity for these folks to save big energy. 

 

You can usually run really low temperatures, which means long, super-efficient condensing cycles.   A Navien Combi or Triangle Tube combi would be great options depending on potable hot water consumption.  The really elegant solution is a mod-con with stainless steel indirect - but may be more $ than they want.  And Navien has really figured out on-demand with their buffer tank and pump/internal or external recirc setup, so indirect becomes less of a luxury benefit.  

 

The red herring is the baseboard.  It may need higher temperatures for adequate conditioning when the weather gets really cold.  Measure it and load calc the rooms it's in.  They'll probably require a separate zone. 

Permalink Reply by Bill Bradbury on July 10, 2011 at 9:40am

First, is this a steam or hot water boiler? It sounds like there is not a main circulator pump, this would indicate steam.

Second, these old girls are usually leaking a bit. This can be a serious problem because the coal sludge has traveled from the boiler throughout the entire system. These big cast iron radiators will hold sludge even after running cleaner through the system for weeks. I know this first hand, on a recent job where I replaced a coal conversion with a mod con boiler, I ended up cleaning the hx 3 times before finally removing every radiator and getting them hot tanked at the automotive radiator shop, then repainted and re-installed. The 10-15% increase in combustion efficiency over a standard cast iron boiler will never pay for the increased cost. Lesson learned.

It sounds like what you should do is; pull the boiler and replace it with a standard cast iron hot water boiler, add an indirect tank with a solar option(2 heat exchangers), replace the 2 baseboards with flat panels(Runtal) and add a t-stat.