The other day I was reading an article on the internet and saw an advertisement that read, "Heavy Broken Hot Tub Covers Waste tons of Energy." I thought,"Hey, somebody get's it!" When I clicked on the ad and went to the website, guess what their selling? Rigid foam spa covers that will certainly end up heavy or broken, typically in only two years. How does this solve the problem of heavy hot tub covers?
Instead of selling something that will solve the problem by not getting heavy or broken, this website was just selling the same thing, hoping no one will be smart enough to notice. If every hot tub owner has to replace their hot tub cover because it broke or got heavy, maybe the question should be, "Is there something better?"
What causes foam Hot Tub Covers to get heavy is the moisture that gets trapped inside them. Rigid foam board is often used in many different types of insulation applications such as the freezer areas in supermarkets and gas stations. Layers of foam board can insulate cool storage areas while the customer area can be kept comfortably warmer. In this particular type of installation the foam is not subjected to hot moist air. As long as the foam remains dry, it has a predictable insulation value. But if the foam were to have moisture in it replacing the tiny air pockets it uses to insulate, it would have no insulation value at all.
If the idea was to create the perfect environment for rigid Styrofoam board to become saturated it would be to put it atop a source of warm, humid steam. It would saturate faster than if it was tied it to the bottom of a swimming pool. Why? Because water molecules are bigger than steam molecules. Steam is able to penetrate much smaller spaces faster than water can. Furthermore, once the steam cools, it condenses back into water, displacing air in the foam as it does this.
Long before anyone notices their hot tub cover getting heavy, moisture has already begun to replace the air spaces in it. The little insulation value that cover might have had, goes down dramatically once this happens. Once saturated the hot tub cover is insulating about as well as a wet piece of plywood. Which is what the advertisement was eluding to in the first place.
A hot tub owner might be duped into thinking that a saturated cover is still insulating well because snow won’t melt off it in the winter. But what most don't notice is that the snow won’t melt off the cover because it is frozen. When temperature drops drastically outside, it freezes the moisture in the cover. The water inside the spa is never in contact with the foam since the foam is resting way up on top of the acrylic of the hot tub, usually around a foot above the water surface. What then happens is the warm spa water evaporates into steam. That steam rises, it rises until it hits the bottom of the frozen hot tub cover. Then the steam cools and turns back into water. The water, now cooled, falls back into the warm spa water cooling it off.
If the design was to cool down the spa water, making the hot tub work harder to keep the water up to temperature and drive power consumption sky high, then mission accomplished. Placing a saturated, heavy, frozen hot tub cover on the spa would be the perfect solution.
However if the goal is to actually cover the spa and save energy, then a better solution to another rigid foam filled hot tub cover would be something entirely different. SpaCap Hot Tub Covers insulate the water from the water surface, without rigid foam.