Bathroom remodel - electric radiant floor heating?

[Ameli0rate]

From those who have it (and my memories of it in Europe in the 70's and 80's) it's amazing and a must-have.

So we're planning a bathroom remodel, and currently have forced air furnace/AC for the house and the master bath has that little Nutone 1950's looking heater fan in the ceiling. It's mostly useless.

What I'm thinking is that I could re-purpose the switch for the Nutone for an electric heated floor, but I know nothing of them.

What do I need to think about? What do I need to talk to the tile/floor contractor about? What brands are good/bad/ugly? This is on the 2nd floor of a 1998 house in Texas.
Will 1500-1800 watts be enough for the floor of the master and WC in a ballpark 20' x 8' of "hallway" between the sinks, shower/tub and closet?
I'm thinking there's no need for heating in the shower or under the tub or sinks, so the master closet and anywhere feet touch the floor.


My idea is to spend a little extra to ensure this is done right and done once. I don't want to have to revisit any of this stuff in 10 years because I cheaped out of parts.

 

[Jadnashua]

FWIW, when going electric, most companies advertise their products as floor warming. Depending on the circumstances, you MIGHT heat the space depending on your conditions. Most are limited to a maximum of around 12-14W/sqft. As opposed to hydronic floor heating which can usually be sized for any heating needs, electric will have some limitations and, generally, electric heating will be more expensive to run.

You MIGHT be able to use the wiring for your existing heater, but that would depend. Note that in some places (CA for now, others may follow) electric floor warming/heating is REQUIRED to be on a timer and cannot be used for general heating. TX is adopting more conservation rules, so you need to be up on what is current.

There are two general methods to do this, either a mat or cables. Mats can be custom ordered for any shape and size. Cables cannot be cut but are available in various lengths to fit many places and are fairly easy to install as they snap in place when used with their mats, or if used without, with clips. EMbedding them in the mortar is easier when using something like Ditra Heat (linked below). Otherwise, the additional step of self-leveling cement is often used to embed them and create a level surface to then tile. A membrane eliminates that step, and is generally quicker to install (time is money).

Here is one cable company that I've played with a little https://www.schluter.com/schluter-us/en_US/Floor-Warming/c/FW

 

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[Ameli0rate]

Thanks, the 12-14W per sqf would be a useful measurement as I can figure out if it will be enough or not.

I'm not looking to heat the house with it, but to keep the room comfortable - which, even if it's only 65f in there, if the floor is 70f, it will feel far more comfortable AND it will work better to dissipate condensation.

A timer or at least a thermostat is a must. I don't want to forget that thing on all day, so thanks for pointing that out too.


On a side note, if I were to go to heated floors (both upstairs and downstairs), it would make sense to use a hydronic system, and in THAT case, it would make sense to use hydronic in the bathroom too. Of course, the cost of 'converting' the entire house and replace all the flooring would be one epic piece of scope-creep.

Downstairs would be the main concern there anyway, so the upstairs bedroom is probably a good candidate for electric in conjunction with the remodel.

Thanks for the link, I'll google around the mats/membranes.

 

[Dana]

12-14 watts per square foot for the whole room would be overkill. If the actively heated floor area is only 1/4 of the square footage of the ceiling it's about right.

A house in San Antonio with some fluffy insulation in the walls can usually be fully heated at outdoor temps below freezing with 3 watts per square foot. Rooms with fewer windows would take less than that. A 70F floor in a 65F room is delivering about 3 watts of heat per square foot, which is probably overkill anytime it's above freezing outside if the floor is a major fraction of the square footage of the room.

 

[Ameli0rate]

That's even better. I'm not looking to super-heat the room, just take the chill out of our feet and alleviate some condensation-on-the-mirror issues.

This is how the bathroom looks: https://i.imgur.com/kr14oya.jpg
Plus there's a 10'x10' (ballpark) master closet on the far end to the right. I'm guessing one does not put heat all the way out to the edges of a closet where nobody walks - it's just hanger/shelf space and there's no need to heat under that. Only where feet actually touch the floor, correct?

 

[Dana]

If you limit it to just where your bare feet would be walking it won't over-heat the place.

 

[Reach4]

12-14 watts per square foot for the whole room would be overkill. If the actively heated floor area is only 1/4 of the square footage of the ceiling it's about right.

If he wants to be able to turn on the heat 30 minutes before bathing and feel comfortable, then more watts would be good.

 

[Dana]

If he wants to be able to turn on the heat 30 minutes before bathing and feel comfortable, then more watts would be good.

Doesn't take anywhere near 30 minutes to heat up a tile floor with 10 watts per square foot going into it (or even 5 watts). With hot tile it's pretty easy to end up "too much of a good thing" if heating it open-ended, without a floor thermostat.

 

[Jadnashua]

FWIW, most floor warming systems limit the floor temp (via an in-floor sensor) to the mid 80's or so. Because tile conducts heat pretty well, as long as it is close to body skin temperature, it doesn't feel cold nor does it tend to 'suck' heat out of you. My bathrooms are heated via hydronic systems and in the winter, the warm floor is nice. That heating is turned off for the summer, but I don't mind the cooler tile then. Properly done hydronic radiant heating is probably the most comfortable way to heat a home and you can typically be comfortable at a lower air temperature than you would be via forced air heat. Think about standing outside on a calm, sunny day in the winter...the radiant sun's heat can make you feel comfy...step into the shade, and it's cold.

If you needed the max output, your electric bill would be pretty high! The thermostats on these things are not proportional...it's either full on or full off, but cycling on/off can easily adjust the overall temperature of the room.

But, if your floor is cold, and you turn the thing on, the floor sensor is going to call for maximum until things warm up. If you're using a more conventional install where you might utilize slc to embed the material, that adds thermal mass which can be nice to moderate things, but it also means slower response times. This is where something like DitraHeat mat, that has a lot of open air space in it and where it places the heating cable closer to the tile can help speed up the response times. There is a minimum tile size limitation when using a mat like this that is overcome if you embed things in slc, but most people use a tile 2x2" or larger on their floor, which is the minimum that system can handle.

There's a lot to consider. Cost for materials, installation, performance, longevity. If you do go with an electrically heated floor, do yourself a favor and put a spare floor sensor in. If you ever need it because the other one fails, you won't have to tear up the floor to install a replacement. They're pretty reliable, but the inconvenience is way more money than a spare done during the original install. Just tape up the lead in the back of the box, just in case it's ever needed.

 

[Ameli0rate]

put a spare floor sensor in.

Thanks, lots of good info to consider and the Ditra site has more - things like not putting heating coils under cabinets, etc.

The spare sensor is the sort of advice that can be/will be worth gold when the first one fails! I'll measure the bathroom a little better this weekend, but it looks like a programmable thermostat (determine how long it takes to heat the floor to desired temp, and how long it takes to cool down after = turn on at 5:45, turn off 30 minutes later, good enough for 0600-0630 bathroom usage) and something like the Ditra system would be perfect.

 

[Jadnashua]

IF you go with Ditra Heat, one sensor comes with the thermostat and a second one with the heating cable so you don't need to source one separately. There are other systems out there, I've played with the Ditra one in a class...it's pretty bulletproof.

 

[WorthFlorida]

I remodel my two bathrooms in the past year and I'm kicking myself for not installing an electric floor warming system. The master bath is on a slab with marble tiles and in Orlando we get quite a few chilly days especially over night. Just to have warm floor to take the chill out of the tile would have been well worth the effort. If you have a power limit, cover the floor area in front of the shower and sinks. It's where you'll stand the most.

 

[Bcarlson78248]

When I bought electric floor warming from Warmly Yours, I sent them a scale drawing of the bathroom and they came back with a layout for the heat system, including exactly how many heating elements were needed and how to lay them out. I assume other companies may have a similar service.

Our system is in a basement bathroom, and its usually set at about 75 degrees for the in-floor sensor. That makes the tile floor feel definitely warmer than the unheated tile in the next room, but not really warm. IIRC, they recommended a max setting of 82 degrees under tile.

We still use a Panasonic combo fan/heat unit to bring the temp up quickly when we need it, but that's because there is no other heat source in the basement. The basement is well insulated, and typical winter temperature in the basement is about 65 degrees when the 1st floor is set to 70 degrees.

Bruce