DIY heat rock question

[Lord-Doom]

I've made a couple of designs using 300x300x11mm thick slate onto a 300mm square piece of MDF, routed with a 6mm bit just deep enough so the cord has contact with the slate. The average number of grooves routed into the MDF is 15, which will bed around 3.5-4m of the heat coil. So for the 30cm MDF the space between each groove is approx 2cm.

Myself and girlfriend (member Xeaal) have been experimenting with 15w and a 25w heat cords and its seems the 25w is too hot and the 15w too cool. The 25w will work perfectly with a thermostat, but wondering if it's possible to make an effective 15w solution.

So what size & type of stone/tile, and wattage do you guys find works well together?

 

[Snowman]

Heat cord is affected by the room temp. So what works now may be too cold in winter. Use the 25 on a thermostat. Better to have it too hot and controlled with a thermostat. You can make it cooler with less runs of cords if you wanted too.