low flow resistance boiler ???
 

In John Seigenthalers writing on Hydronics for low energy housing one of his illustrations refers to a "low flow resistance boiler". Anyone one know if an electric micro boiler would be considered this? I am looking for an electric heat source for a 500 sq' single zone hi-mass hydronic floor suppling low temp water off peak.

DIY one out of a window A/C and coax coil heat exchanger.