[Shop-talk] Hydronic system off a steam boiler?

[Jim Franklin]

Thought I'd toss this out there in case any boiler people were  
lurking...

I have a steam system serving my first floor. It also provides  
domestic hot water by heating a SuperStor tank, feeding boiler water  
to the SuperStor coil.

I'm adding 3 hydronic zones to the house- a small laundry room in the  
basement, a 250 sf addition off the kitchen, and a 1000 sf 2nd story.  
I have the BTUs available in the boiler (31,000).

I'd like to supply the hydronic zones from a storage tank that was  
heated by the boiler much like the indirect DHW, but the indirects are  
really pricy. A 45 gallon SuperStor is about $900, an 80 gallon is  
$1800! (add in a 2nd coil for solar and it's $2700. Jeebus.). And  
since they are designed for high transfer rate of DHW, I think they're  
overkill. But I haven't found anything less intense.

Has anyone used a different storage tank for this application? Say, a  
burned out electric water heater? I could use the tankless coil  
included with the boiler to heat the storage tank; it's supposed to  
give me 4.5 gal/min of boiler-temp water, which will recharge BTUs in  
26 minutes with a 30 degree temp diff. A 60 gallon tank would require  
3 recharges per hour, about 10 mins each. (hope my math is right, it's  
stll early)

thanks,
jim