How to Figure the R-Value for Hearth Pads

Hearth pads serve as bases for heat producing objects such as wood burning stoves or fireplaces. The hearth is intended to protect your floor from the heat the objects produce. As such, it’s important that the hearth be made of fireproof material. It’s also a good idea to have material that contains as high an R-value as possible, with the R-value representing the insulative efficiency of the material. All materials have a general R-value, with the value rising with the material's thickness. This makes it a simple process to figure out the R-value of your specific hearth. All that’s needed is a good R-value table, and a list of the materials from which your hearth is constructed.

Tape measure
R-value table

Instructions

- 1
  Examine the pad to determine if it’s made of a single material or multiple layers of material sandwiched together. Measure each layer of material with a tape measure and mark the height of each layer on a piece of paper along with the material type.
- 2
  Consult an R-value table to find the R-value of each layer of material by type and thickness. Mark the R-value of each layer down onto the paper next to the layer listed. For example, a layer of 1-inch-thick poured concrete has an R-value of 0.08, whereas a layer of brick that’s 4 inches thick would have an R-value of 0.8. See the Resources section for an online R-value table.
- 3
  Add the R-values of all of the materials in the hearth together to figure the R-value of the hearth pad as a whole. A hearth with a 4-inch brick layer topped with a slab of 1-inch-thick concrete would have a total R-value of 0.88 (0.08 + 0.8).

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