Agree with Shaughnn. With the heat just below the tile, there's very little "R-value" that the heat needs to go through to get to your feet. With the heating elements underneath the subfloor, in the joist bay, you're adding a bit more resistance to heat travel, plus with the heating elements under the subfloor, best construction practices would dictate that insulation with a radiant barrier be added in the joist bay beneath the heating elements. My own persona rule-of-thumb is to have 3-times the r-value under the radiant heating elements compared to the R-value on top of the heating elements. Having insulation under the heating elements helps direct the heat upwards, versus it heating the joist bay, the ceiling beneath, or the basement beneath. Now after writing all that, I will say that I do differentiate between whole house primary heat and the smaller comfort mats used to simply take the edge off of cold tiles. If this is "whole house heat" and it'll be on most of the winter but not used in the warmer months, then under-the-subfloor is fine. If this is "comfort heat" to simply warm up cold tile, and it'll be used year-round, then you'd want a quicker response time and I recommend what Shaughnn wrote, having the heating elements just under the tile.

A friend of mine has heating coils under all her floors. She said that it takes time to get used to this type of heat. Most of us are used to turning up the thermostat to get the heat to "kick on". But with subfloor coils it takes a long time to heat up all of the floor mass before the floor mass can then adequately radiate heat to warm up the room. From what I remember reading back when I was looking into this . . . you end up spending more money/energy with this type of heating system. I like to turn down the thermostats when we aren't home all day and then inch them up a tad to make the furnace turn on when we get home. You can't really turn the heat down with these floors because if they cool down they take a while to recover. Correct me if I have this wrong. People say stone floors are cold. They are no cooler than the wood floors in a home. They may feel cooler . . . but they are no more cooler. It's physics.

Elisa, go for what you want. I really like the light tile you are leaning towards especially laid in a different pattern. I have the grey wood laminate throughout my house and Love It! It hides dog foot prints and fur like no other flooring I’ve ever owned. I do clean my house regularly but if we get drop in company on Thursday night and I haven’t had time to vacuum or mop since the weekend unless they get right down on the floor, you aren’t going to see it. Out laminate is in the kitchen with no problems.

We are remodeling our kitchen and turning our sunroom into a family room. The sunroom windows are not very efficient so we are installing hydronic floor heating into the space. We live in the Midwest so it is cold here 8 months out of the year. We have heard that porcelain tile is a better conductor than ceramic tile. Does anyone have any knowledge on this? We would like to do a 3x9 matte black herringbone tile but are only finding it in ceramic and it is rated for low traffic areas. The tile is also going in the mudroom/entry into the house. Any thoughts?