A couple of houses ago, I had a dedicated oil water heater, made by Boch (sp). The only way I could run out of hot water was to fill the two-person hot tub at full speed. It couldn't quite keep up with that. But a normal shower, etc, didn't even tax it. It could recover from a cold fill to 160Âº in about 20 minutes or less. I liked it because it gave the furnace a break during the summer, and the heating requirements didn't affect it during the winter. I now have an oil/hot water furnace the provides the DHW. It doesn't run much since the pellet stove arrived - yeah!