Hi Mark: The cost of running a whole-house tankless electric unit (Seisco RA28 for example) versus a 40gal gas tank, is about the same. This is based on gas costing 40% less than electricity, that's on average, nationally. A tank water heater, however, runs out of hot water pretty quickly. A tankless never does! Yes to your second question: There are gas units designed to heat as little or as much hot water as you need. I sell both electric & gas models and will gladly e-mail you information on both. I currently have 19 tankless models (combined elect' & gas) available, from three manufacturers: Microtherm, G.E. & Bosch. My # is 800 851 9891 during regular business hours (central time) I hope this helps. Regards, Brian Wood. P.S. I'm installing one of each, side by side, for a customer who is being cautious in case the lights go out at midnight on Jan 1st. Something to think about.