I have an older (2003) Coast spa that needs a new cover. I have been looking at several vendors and have some questions about the insulation. Most covers are rated in R values and my question is if the temperature outside ranges from 30 to 110 degrees how much does the R value really matter. Will I see a difference from an R14 to R21 in my temperature range? My tub is 92" X 92" with 7" radius corners. My dealer quoted me $600.00 for a new one but I have been looking online and I can get one much cheaper.

First off, be very careful comparing different websites claims as to R value. different sites make different claims, for the EXACT same cover thickness. I've seen the same cover being advertised as R-14 at one site, and R-25 at another. How some of these site come up with some of their numbers is beyond me (well, actually, I do have some ideas, but it isn't worth taking the time to try and type out the full explanation. Basically though, there's different R value testing procedures that can each give different results). What's most important to know and keep in mind is that if the cover has the same thickness and same density of foam as another, it has the SAME R value.....regardless of the "claim".

As far as R value mattering or making a difference...next winter try this little test. Put on a sweater and go out side... Then put a jacket on over the sweater (increasing the R value of your outer wear). Which keeps you warmer (thereby reducing the heat loss from your body)? While there is a point of diminishing returns (e.g. the cost of the insulation exceeds the $ savings you'll realize in heat loss savings) I don't believe spa covers have quite yet reached that point.

I did a simular test

2 inch flat cover versus a 6x4 sloped cover.

Temp 40 degrees

pump/heater run time 4 to 6 hours with 2 flat cover, 2 to 4 hours for 6x4 cover. to reach 100 deg water temp

R values does make a big difference, espc in the power bill ea month.