Tina,

We are just finishing up a new bath in zone 4 (MN) with marble basketweave floors. I did the in-floor radiant heat, and it feels MORE than adequate to heat the bathroom. However, building code in our area requires that there must be a secondary heat source. We put in an electric toekick heater under the vanity. In your case, since you already have a radiator in the bathroom you could do a hydronic toekick heater. (We have those elsewhere in the house to replace some ancient radiators and they're great!)

I have marble floors in my powder room and they are freezing cold. Not a big deal since no one ever has bare feet in there, though.

If you look at the "best bath decisions I made" threads, countless people mention their heated floors as being the favorite feature.

HTH!

It should be enough. Interestingly, many of the bathrooms in my area (Phila) have no heat in the bathrooms, relying solely on the small size and the heat from the shower to heat it temporarily, so maybe I think anything would be enough.

The safest answer is to say that numbers need to be run on the room to figure out your BTU requirements. Depends on interior wall, exterior wall, windows, insulation, the ceiling, etc.

As to how many BTUs electric RFH can supply, that's dependent on how many square feet of mat you can put on the floor and what system you choose.

Bathrooms generally lose out in the floor-to-wall ratio due to tub, shower, toilet and cabinets taking up floor space.

When you shop for a mat, look at its BTU/sqft output. It's directly correlated to the mat's watt consumption. The maximum you'll find with any above-floor electric FH system is 15watts per sqft (51BTU/sqft), the most common is 12w/sqft (41Btu/sqft).

Technically, yes, a mat could put out enough BTUs to adequately heat a bathroom.

If you do install electric in-floor and electric baseboard, the baseboard can be secondary to the floor mat.

I'm assuming you are going to install a fan? If so, why not get a panasonic with a heater? They work great see link below

Here is a link that might be useful: Panasonic fan with heater and light

If you don't mind a really cold toilet seat and waiting 5 minutes for the hot water to warm up the shower, then it might be "enough" if the house is well insulated. It will never heat the room to 65 degrees when it's 20 outside though if this is the typical under insulated older home.

I have radiant floor heat and a heated towel bar/radiator. And I still often turn on the overhead heat lamp when I get undressed!

The floor heat is wonderful -- highly recommend. There are some places around the toilet and at the back underneath the washstand that don't have the heater cords underneath and you can really feel the difference!

Thanks for all the input; it's been really helpful. Shanghaimom, I did a 'step test' with a 12x12 marble sample I had on hand, and you're right; it is so much colder than the tile. That has convinced me to install floor heat, even if it's only a secondary source. I had no idea that hydronic toekick heaters existed; the quotes I got all mentioned 'electric fan toekick heaters', and I didn't want to go that route. When discussing with my contractor last evening, he was very supportive of the hydronic solution; now I just have to make sure that the unit will fit under the 'door' side of my vanity (will need to access it for service, so it really shouldn't creep into the drawer side of the cabinet.) Fingers crossed!
Mongo, thanks! I'll do my homework on the BTU calculations; thanks for pointing out what to look for. Lynneblack, thanks for the vent/fan/light combo idea. I've read on the boards that the Panasonic is a great unit, but one of the two items I'm keeping from the current bathroom is my Nutone melon vent fan/dimmable light.