Joni, from Denver Colorado writes:
Hi Pros,
I have been shopping for a replacement spa cover for my old, and now very waterlogged, cover. I have seen so many different cover thicknesses advertised. How do I know which is right for my needs?
I look forward to your answer.
Four inch tapering to two inch spa cover
Center thickness
Hello Joni,
You have asked the most important question for 98% of spa owners replacing their tops. We will be glad to explain below. Our answer will be based on the assumption that you are looking for a cover that will insulate very well, to keep your heating bills as low as possible.
The key fact is that the thicker the cover, the better it will insulate.
From there, consider the difference in pricing from the typical four, five or six inch thick covers. If the six inch thick cover is $100 more than the four inch thick cover, it would make sense to go with the thicker cover IF you will save more than the $100 extra cost over the life of the cover. As you live in Denver, if you keep your spa hot year round, The Pros believe the extra two inches of insulation will save over $100 during the typical five year life of your cover. To win, you would only have to save $20 per year. If it is really cold, lets say around zero degrees, you can save $20 in a single month!
Thicker covers insulate better as shown by the R-factor. R-factor is a rating of the insulation value of a product. The pink insulation in your attic has an R-value associated with it and so does the foam inside a hottub cover. With both, the R-value is calculated by multiplying the R-value of the material times the thickness of the material. For example, 1.0 pound density foam has an R-value
of 4.17 at 4o degrees Fahrenheit.
- A 4-2 tapering cover has an average thickness of 3 inches so it would have an R value of 3 X 4.17 = R12.51
- A 6-4 tapering cover has an average thickness of 5 inches so it would have an R value of 5 X 4.17 = R20.85
That is an increase of 67% in the R-value for the extra $100.
If your hot tub is in a gazebo or an area protected from the weather, keep in mind you can also get covers that do not taper. This changes the R-value calculation above a bit.
- A 4″ thick and flat cover has a thickness of 4 inches so it would have an R value of 4 X 4.17 = R16.68
Keep in mind that although the flat cover has an R-value that is 33% higher, it ALSO does not have any areas where the cover is only 2 inches thick that can contribute to heat loss.
Happy Tubbing!
Ethel Elliott
