Post date: Dec 12, 2014 1:56:35 AM
The shower in in a little projection that just out from the east side of the house. My architect likes little bumps in the walls, saying that the outer envelope of a Pueblo style building needs to show the rooms inside.
In this case it means that - within the Solar Slab heating design - there is no way to heat the shower floor. The concrete ducts that transfer heat to the floor slab do not pass under the shower and there is no way to make them do so. And I suspect that conduction through the concrete will not suffice.
So the architect suggested using an electric heating pad under the floor tile. At first I balked - thinking that I don't really need this, since I shower in a cold cast iron tub at present. But then, I figured that future owners might want warm tootsies while they shower. After that I thought that future owners won't test the heat in the floor so why bother? One more thought says that for about $200 in materials, why not install it now?
Turns out that the thermostats that control these heat pads use a sensor installed under the floor. I didn't want to control the heat based on the temperature of the air in the adjacent bathroom, but am more comfortable with a sensor in the floor. It is the tile I want to warm. The air gets heated by the sun in adjacent rooms and transferred through the bathroom floor - but not, as I said, to the shower floor. (There is only a west-facing window in the shower stall - to provide light - but I might get some heat from the sun in the mornings.)
I don't plan on heating the shower floor all the time - only when I take a shower. I could theoretically calculate how long it will take to raise the tile temperature from 50°F to 80°F with 12 Watt per square foot of heat mat, but I think I'll just wait and test it.
Unlike the rest of the floor in the house (which will be built - bottom up - with gravel, insulation, concrete blocks, concrete slab) this one will be built with gravel, concrete slab, insulation, backer board, heating mat, tile. That is, the insulation will be immediately under the tile assembly instead of insulation under all that concrete. I don't want a lot of thermal mass in the shower - I want it to heat quickly.