Contractor number one says that I need to go to a water boiler system instead of a geothermal system because the hardwood floors and carpet are insulators and the geothermal system does not put out enough heat. Contractor number two says the thicker the flooring the better. Carpet, wood, the more wood the better, more insulators means better thermal mass and geothermal heat is perfect for my application. Which contractor is right? Read my other post for more details. Thank you!

Please add a link to your other post.

Contractor number one is the winner.

Geo-thermal (besides "burning" electricity) will not produce water temperatures much above 120°F with efficiency (might as well buy an electric boiler). This is fine for certain contruction e.g. slab-on-grade or basement slabs, but too low for many sandwich nearly all sub-floor radiant floor heating systems.

As for thermal mass; his argument is nonsense. Have your contractor produce a sample of his heat loss analysis. This is where smart guys start a radiant floor design as it is the only way to determine which system will work at a specified i.e. predetermined design water temperature.

It sounds like some serious spreadsheet work (and some research) is necessary here. Heat flows in - all - directions. If the area below the radiant pipes is not insulated, it will be much more difficult to heat the floor above. If you know the material layered in the floor, and its thickness, you can likely find the R value of those materials on the internet. Once you know the R value of the floor system, you can use the heat load calculation for that room to see if geo can produce temps high enough to go through the floor and heat the room.

Of course, there is another answer.... if both contractors are reputable, and will back up their work - in writing - , choose the one with the answer you want. :-)

Regards,
Ed