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We are choosing between laminate and plastic flooring over water based underfloor heating (heat pipes laid in the screed floor over thick concrete). Laminate floorings have a thermal resistance of app. 0.06 m^2K/W, plastics (for example Classen NEO) have halve of that or less.

While plastics are twice as good in terms of thermal conductivity, they are also more expensive, may be harder to install (linoleum has very low thermal resistance but needs to be glued to the underfloor) and there are environmental and air quality concerns for the cheaper options (vinyl).

How do I find out what the consequences of higher thermal resistance (lower thermal conductivity) really are, in terms of how much more m^3 in gas I will need each year? Are there any calculation tools, lookup tables or rules of thumb to help me with this? Maybe experiments with different floor types?

I could calculate the difference straight from the theory, but I don't even know what the average floor heat is from underfloor heating (from this, I imagine, I could calculate back the energy difference for different floor types, and then I would need specs of the heater to calculate how much more gas this would cost).

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Respectfully, you are trying to compare apples to autos here.

Burning gas makes things hot.

Thermal conductivity is just how fast it takes the heat to get to you.

I suggest you go try to calculate it from theory, physics is fun, calculus is interesting, the numbers will not lie to you, and you will see the logical error immediately.

The heat has to go somewhere. A metal floor would get hot fast, and cold fast.

A concrete floor will get hot slowly, and get cold slowly.

If your floor has a very low thermal resistance - you would be able to feel the path of the heating pipes/elements. It would have hot spots and cold spots.

With a high thermal resistance the entire floor will feel the same temperature.

  • …Unless the floor is insulated on the bottom with a substance with lower thermal conductivity than the flooring material. Unlikely, but that would change the heat flux. – iLikeDirt Mar 30 '15 at 23:31
  • From what i understand, the pipes heat the concrete around them, diffusing the heat, and the heat rises up through the floor covering (linoleum or laminate) to heat my feet. The floor under the pipes is thick concrete while the layer of concrete above the pipes is just a few centimeters. – Ivana Apr 5 '15 at 13:28
  • You should be totally fine with any floor covering, unless the concrete slab has no insulation under it, in which case you will probably NOT be fine, no matter which floor covering you choose. – iLikeDirt Apr 5 '15 at 13:57
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Aside from the factors mentioned by "Some Guy", note that the relatively still air next to surfaces also has an insulating value. A rough estimate for many common cases would be about 0.1 m^2K/W. For thin assemblies, this air film dominates the total heat transfer and means the insulating value of the materials themselves have very little impact on the overall heat transfer.

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The most honest answer is, "it doesn't matter." Assuming the worst case scenario that there is no insulation of any sort beneath the pipes, a flooring material with a lower thermal conductivity will cause a small amount of the heat to be directed downwards rather than upwards, but we're probably talking about a difference in the number of watts/BTUs that can be counted on two hands, for the cost of pennies/Euro cents per year on your gas bill. It's background noise, unless you're talking about a floor of tens of thousands of square feet, in which case you're probably running a business and should have this calculation done by a professional.

  • Do you have a reference for this? – Ivana Apr 5 '15 at 13:46
  • Basic thermodynamics? – iLikeDirt Apr 5 '15 at 13:56

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