I am shopping for a replacement hot tub cover. I see now covers are made in both tapered and in flat versions. Other than the lost ability for rain water to run off the tapered cover, what is the reason I should consider a flat spa cover?
John from Cincinnati, Ohio
Hi John,
Lets see if we can help you to understand the difference between tapered covers that slope to the edges, and flat covers.
A 4-2 tapering cover on top of a 6-4 tapering cover for comparison
Covers are made with a slope so rain water does not pool on top of the cover. This works very well for the rain, but compromises the insulation the cover provides at the same time. For example, spa covers are measured with what is known as the R-value, which is a measure of the ability of a cover to keep the heat in. The R-value is determined by the thickness of the insulating material.
To calculate the R-value for a tapering cover, the average thickness is typically used. For example, if a cover tapers from five inches thick in the middle to three inches thick at the ends, the R-value will be based on an average thickness of four inches.
Mathematically then, a 5″ to 3″ tapering cover will have exactly the same R-value as a 4″ thick, flat cover. In reality however, the tapering cover has two very large areas where the thickness is less than 4 inches, and those will allow heat to escape at a rate that is much faster than a 4 inch thick area. So in practice, the tapering cover will perform worse in keeping the heat in than a flat cover.
Flat covers also offer the benefit of greater strength, to hold snow weight, etc.
Happy Tubbing!
Ethel Elliott
