Snow pile on spa cover
Cliff from Raleigh North Carolina writes,
Hi Pros!
Thank you for so much tremendous information about replacement covers. One question I cannot find the answer for, pertains to the R-value. Can you speak to the R-value considerations with hot tub covers?
Thank you for your time!
Hello Cliff,
Let me see if I can help untangle the mystery of R-value when it comes to hot tub covers. In general, the R-value is a measurement of the ability to insulate of a given material. Specifically, R-value is, per Wikipedia:
“The R-value is a measure of thermal resistance. Under uniform conditions it is the ratio of the temperature difference across an insulator and the heat transfer per unit area. The R-value being discussed is the unit thermal resistance. This is used for a unit value of any particular material. The higher the number, the better the insulation’s effectiveness.”
R-value for replacement hot tub cover EPS foam
To the right is the specification sheet from one of the manufacturers of expanded polystyrene foam, or EPS for short. Note the R-values are shown based on how the EPS will perform at 40F and 75F.
However, the most important factor in determining the R-value is the thickness of the foam, as shown in the Units column. The R-value is determined by multiplying the R-value times the number of inches of thickness.
In short, this is why thicker covers insulate better, because the base R-value is multiplied times the thickness!
The next most important factor is the foam density, shown in the first row in the report. This serves to illustrate that the density adds relatively little to the R-value. Greater densities do add to the strength properties of the foam however.
Hope this helps explain!
Happy Tubbing
Ethel Elliott
