I plan on installing an electrical tankless water heater in my house. I currently have hot water supplied from a coil in my furnace boiler. Can I connect the input water supply to the tankless unit from the output water supply from the coil in the boiler? During the summer the boiler would be turned off and the water would just pass through the boiler coil but during the winter months when I'm heating my house, I would like to take advantage of the hot water coil, and delivery hotter water to the tankless heater. Will I need to limit the input temperature to the tankless unit and if so, how would I do that?