# Underfloor heating and how R values affect it

I am moving into a new house that has underfloor heating (wet system) throughout the ground floor.

I am trying to decide what flooring material to use. (tile or wood)

I know that tile will be a better material, as it will allow heat to pass through more easily. My understanding of this is based on the materials R value

But I am wondering how can I calculate, or even roughly know, how a materials R value will affect the heating costs?

For example, given these values, (both 7mm thick)

• 0.02 -> Ceramic Tile
• 0.25 -> Engineered Wood

Does this mean tile is ten times faster to "feel" hot? i.e. if it takes 10mins to heat tile surface to 12C, will it take 100mins for the wooden floor?

Or is R value simply not important or not a good indicator of heating times or potential heating costs?

You're correct to assume that tile will transfer heat more quickly. However, since it's much more dense than wood, it also requires more heat energy to reach a certain temperature. For that reason, heating time is normalized somewhat.

When discussing energy efficiency we have to look at where the heat can go other than through the flooring. The R-value of the flooring is irrelevant in a scenario where there's perfect insulation below and alongside the heat source. All heat must transfer through the flooring in that case. Therefore, the insulation that was installed below the heat source is the critical factor. If you have a good layer of foam below the heat source, either flooring is probably fine.

• Thanks for the clear and concise reply! Makes a lot of sense now. Sadly I'm not sure about the insulation under the heat source... builders put that in. I must find out about it. Commented Sep 9, 2016 at 21:44