What is the R-Value of a Hot Tub Cover, and What Does it Mean?
Ideal™ Spa Covers
The R-value is a measure of thermal resistance, or ability of heat to transfer from hot to cold, through materials (such as insulation) and assemblies of materials (such as walls and floors). The higher the R-value, the more a material prevents heat transfer. R-value depends on materials’ resistance to heat conduction, as well as the thickness and (for loose or porous material) any heat losses due to convection and radiative heat transfer. However, it does not account for the radiative or convective properties of the material’s surface, which may be an important factor for some applications. R varies with temperature, but in construction, it is common to treat it as being constant for a given material (or assembly). It is closely related to the thermal transmittance (U-value) of a material or assembly, but is easier to manipulate in some calculations since it can be simply added for materials and assemblies that are arranged in layers, or scaled proportionately if the thickness of a material change.
Simply Stated: The R-values Are A Measurement Of The Materials (Foam Panels In Spa Covers) Ability To Resist The Conduction Of Heat Flow Through A Solid (Loss Of Heat)
To help the consumer compare the R-Values, certain standards have been put in place for industries to follow when referring to their products. The following information has been put together to help you the next time you are considering purchasing a spa cover.
1) In the case of spa covers the R-Value should reflect ONLY the foam itself Ideal™ Spa Covers then seals the foam inside the VPB3000 and uses the highest quality marine grade vinyl, which increases the R-Value; this should not be reflected in the advertised R-Value.
2) The R-Value will increase as the air temperature on the cold side of the insulation decreases. In other words, if you tested the insulation at 75 degrees Fahrenheit and then again at 25 degrees Fahrenheit, you will get a higher R-Value at 25 degrees Fahrenheit. ASTM has not specified a temperature that spa covers need to be tested. However, the air temperature must be disclosed when an R-Value is stated.
The chart list R-Values for different foam types, both thickness, and densities. Ideal™ Spa Covers use Expanded Polystyrene Foam (virtually every spa cover is made using this insulation). To calculate the R-Value of tapered foam, the average thickness of a 96″ x 96″ (8ft x 8ft) spa cover was used. If the size of your spa cover is smaller, the actual R-Value will be higher than stated in the chart. This is because the outer edge of the foam is cut to make your spa cover and the outer edge will actually be a bit thicker. (Example 8′ x 8′ (1.0 lb) spa cover the R-value is 13.2. Reduce the size of the spa cover to 7′ x 7′ and the R-Value increases to 13.55).
The R-values Below Are Based On A 96" X 96" Spa Cover
Smaller Covers Have Higher R-values
“True” R-Values are for the foam ONLY.
Although covering foam in marine vinyl does increase R-Values, it is NOT supposed to be included.
The Ideal™ Spa Cover 5″ x 3″ with Super Foam (1.5 lbs. density) has an R-20 Value for the foam alone. All Ideal™ Spa Covers are then vacuumed sealed in our own proprietary plastic VPB3000 vapor proof barrier, use the highest grade marine vinyl, have unique “dual purpose heat seal gaskets,” and built-in protection at the seam from heat loss. All of these characteristics increase the insulation value of the cover beyond the value of R-20.
We at Spa Covers Etc., hopes this bit of information has taught you a bit about R-Values and the next time you are shopping for a cover you will have enough background to ask some intelligent questions and you will be able to realize when something is just “too good to be true”.