I read in another thread about the use of hybrid water heaters, Instead of thread hijacking I thought I would open a new one. I am intrigued by this idea of using a hybrid water heater. I am going to be remodeling my downstairs bathroom/utility room. I want to use my existing Series 7, and use my existing electric water heater as my new buffer tank and then use a new water heater as a primary tank. I see that the geospring 50 gal is $899 and my co-op offers a $650 rebate for stand alone Heat Pump Water Heaters. (I am trying to get clarification from there on their wordage of heat pump water heater) Wouldn't using a geospring reduce the efficiency of the Series 7? How does using the DSH in the winter affect the efficiency? Do most people turn of the DSH in the winter? What would be the best situation for this situation? I have a 5 ton series 7 and a 10kw electric heat strip. I live in Iowa and winters can get cold. I have yet to have the electric heat strip turn on (only had geo one winter). Thanks for the advice!