Cheap storage tank?

Jim Franklin

I have steam on the 1st floor with an indirect that uses boiler water through the coil. I'm adding 3 hydronic zones to the house (small laundry room in the basement, addition off the kitchen, entire 2nd floor) and would like to use a storage tank instead of a plate heat exchanger. But the prices for a nice coil-in tank like the SuperStor are just way out of reach. Are there any cheaper ways of achieving the same result?

For instance, how many BTUs can I expect to extract from the tankless coil in the boiler? Would it be reasonable to use an old gas or electric hot water heater plumbed to the coil using tees on the drain & TP openings? I have 31,000 BTU heat loss in the 3 zones, so at 20* delta T I need 3.1 GPM which is within the 3/4" fitting sizes of the water heater. Can I get 3.1 GPM of 180* water from that coil? The boiler's net output is 156,000 BTU.

thanks,
jim