I can't tell you about code, but from a practical standpoint, I sure isn't what I'd do. When the water heater needs replacing, you will have to disconnect the furnace pipe. I can't see in the picture where the line come from, but I'd go up, across, and down to the furnace. This probably could be done with ready cut and threaded pieces of pipe plus a few fittings. On a different topic, what is the hose connected to the water heater drain valve for? Many of us remove the original valve and replace it with a ball valve. Works better than the el cheapos they put on at the factory. I would not leave a hose running across the floor unless I was draining the tank.