We are adding a second floor to our house with a master bedroom and bath. The bath is under a shed dormer and it is over a unheated covered porch. We have very little room in the bath for the baseboard heating which we are using in the rest of the house so we are looking at electric underfloor radiant heating. We do need this as a supplemental heating source for this room. Any experience or suggestions?

If you have a vanity, you might also consider a toe-space heater under the vanity. But beware, there are cheap toe-space heaters, and good quality toe-space heaters. Be sure you get a good-quality one, or you'll be replacing it every two years. The good ones use hot water piping, and come in various heating capacities.