I have a direct vent water heater in an attached garage. The water heater sits adjacent to the exterior wall it vents to. I would like to replace it with an atmospheric vented water heater. I can get a more efficient, larger, and dual anode atmospheric heater for the price of a basic direct vent heater. The folks in the big box stores are telling me there is no way to install an atmospheric heater without running a duct through the roof of the house. Are they correct?