Greg, I put a 1800sq ft addition onto my house about 3yrs ago and installed a whole house hot water heater from Home Depot (Aqua Star 240fx Brand). It works great, but only use it for one shower, a jaccuzi tub two sinks and a bar. I still use the same old tank for the original part of the house. Have filled the tub while the shower was going with no problems. Sure is nice to have constent hot water. They do require a different flue pipe than your current hot water heater. Not sure about any cost savings because everything was added at the same time. The cost of the unit was just under $1000.....Doug