A power vent water heater has a small fan on top that pushes exhaust out a plastic pipe through the wall, so it doesn't need a chimney. Plenty of older Holt and Delhi Township houses still share a brick chimney between the furnace and the water heater — and when the furnace gets swapped for a high-efficiency unit that vents out the side, the water heater can be left alone on a flue that no longer drafts right.