To create holes, use a brace and bit to drill through the flooring, and then a keyhole saw to widen the entrance. Make sure that the holes are not exactly above a floor joist when you drill them. In fact, the joists & studying must be spared as much as possible while installing the water heater equipment.
For a few months, snow covers the foundation, ice sits near the walls, and everyone is too cold to care. Then April and May show up, the snow melts, the sun hits the exterior, and suddenly you notice the house has a few “surprises.”