Would a Water to Air heat exchanger ever work in place of a copper coil to heat water storage? I have a friend who is convinced it will but I don't think it will work. My boiler is only going to "charge" my water stoage, I then have an open loop that will supply the house with heat and DHW. The advantage of the Water to Air H.E. would simply be the cost. I large H.E is only about $200. Since I have the open loop to the house I could even direct the return water past the exchanger. I know that for a water to water exchanger to work it's all about surface area, and with a Water to Air H.E. there will be less copper, but the alum. fins would help, I guess. I don't know about this idea, but it might be worth talking about?