Put a hydronic toekick heater that is concealed under the 36" updated vanity.

Mark Bischak, Architect, I already have one in place. Unfortunately most replacement vanities today look more like furniture with decorative legs or are off the floor which I like. In which case the hdronic unit would be an eyesore. I wanted to stay clear of the "Home Depot specials" look. I guess there is no really good answer unless I do a complete demolish.

"I don't want to rip up the floor"

What pipes and other stuff are underneath the vanity?

"...most replacement vanities today look more like furniture with decorative legs or are off the floor which I like."

What is the condition of the tile underneath the vanity? Do any pipes extend through the floor?

@shirlpp: "If you eliminate the toekick you can put in a wall mounted electric heater."

The heat would flow onto the underside of the new vanity.

The first thing I would do is remove the vent grille and figure out what is underneath the current vanity. Is the current heater an electric type with heat strips or is it part of a forced hot air heating system? You want to replace the current 72 inch vanity with one which is 36 inches. Are you planning to install the new vanity against the right hand wall, or center it where the current vanity is located?

If the current heat is electric and you like the vanity with the feet, then the installing an electric heater in the wall next to the vanity may be a good option. If you have a forced air system and there it there is a connection to the floor through the tile, then adding a floor register next to the vanity may be possible and you can avoid tearing up the floor.

FYI I bought a very nice vanity with a undermount sink and granite countertop with feet from Home Depot last year. It was available on line only. Very different from what you find on display in the store.